Ag/YBCO superconducting round wires fabricated by bimaterial 3D printing

Ag/YBCO superconducting round wires fabricated by bimaterial 3D printing | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Ag/YBCO superconducting round wires fabricated by bimaterial 3D printing Xingyi Zhang, Fenyan Zhao, Baoqiang Zhang, Xiyang Su, Yantang Zhao, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7301425/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract YBa2Cu3O7-δ (YBCO) superconductors have been widely applied in fields such as power electronics, due to their high critical temperature and excellent current-carrying capacity under high magnetic fields. However, long-length round wires, with the greatest potential for power transmission and large-scale magnets, still face challenges: due to the material’s intrinsic brittleness, difficulties in ensuring structural integrity and uniformity during sintering, and ineffective control over crystallographic texture within the round-wire geometry. Herein, we present a direct-ink-writing bimaterial 3D printing strategy to continuously fabricate submillimeter-diameter Ag/YBCO composite wires. Silver paste and ceramic slurry are used as precursors to form core-shell filaments. During the sintering process under an oxygen environment, Ag+ incorporates into YBCO lattice, which forms coherent interfaces with the superconducting phase and promotes [001] grain growth in round-wire. This texture forms intrinsically through solid solution, distinct from conventional seed-mediated or buffer-layer-assisted methods. Electrical transport measurements achieved a transport critical current density of 1.27×104 A·cm-2 @26 K, along with a high bending fracture energy of 1361.8 MJ·m-3. This work paves the way for scalable fabrication of long-length and high-performance superconducting round wires for magnets and compact power transmission cables. Physical sciences/Physics/Condensed-matter physics/Superconducting properties and materials Physical sciences/Materials science/Structural materials/Composites Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Main Text The industrial-scale production of Nb 3 Sn/Cu and NbTi/Cu composite wires with diverse cross-sectional geometries, including their cable-in-conduit conductor (CICC) forms, has advanced low-temperature superconducting applications 1 . However, their use in high-field magnets remains constrained by high cooling costs and low irreversibility fields 2,3 . Since the discovery of YBCO superconductors with a critical temperature ( T c ) above the boiling point of liquid nitrogen (77 K) in the late 1980s 4,5 , nearly four decades of research and development have led to the establishment of a diversified application system for this material. YBCO bulk superconductors demonstrate significant application potential in high-power fields such as magnetic levitation systems and high-field permanent magnets 6 . In low-power applications, epitaxial YBCO thin films, owing to their exceptional superconducting properties, are widely employed in advanced devices such as superconducting quantum interference devices (SQUIDs) and superconducting filters 7 . Meanwhile, second-generation (2G) high-temperature superconducting (HTS) tapes, based on coated conductor technology, have emerged as key materials for power cables and ultra-high-filed superconducting magnet 8,9 . For applications of YBCO in the power sector and large-scale magnet systems, the most promising structural form is long-length round wire 10,11 , the realization of which relies on the controlled fabrication of high-performance superconducting wires. However, the fundamental challenge lies in the ceramic nature of YBCO, which exhibits intrinsic brittleness that complicates wire fabrication and handling 12 . Structurally, the YBCO unit cell consists of layered stacks (sequentially: CuO chains, Ba-O layers, CuO 2 planes, Y layers, CuO 2 planes, and Ba-O layers), with superconductivity primarily originating from electron transport within the CuO 2 planes ( a-b planes) 13,14 . This necessitates well-controlled crystallographic texturing to achieve high superconductivity. Due to this structural peculiarity, it has remained challenging to realize an engineering wire architecture for YBCO analogous to the round-wire composite structure used in Nb 3 Sn/Cu conductors 15 , which is essential for integration into cable and magnet systems. As early as the 1990s, researchers attempted various methods to fabricate YBCO superconducting round wires. Among them, the powder-in-tube (PIT) method emerged as a representative technique, in which YBCO superconducting powder was encapsulated in Ag or Cu tubes, followed by cold working processes such as drawing or forging 16,17 . However, the intrinsic brittleness of YBCO ceramics led to severe grain structure damage during cold deformation 18 . Although post-annealing was employed for structural recovery, the dense metallic sheath hindered oxygen diffusion during heat treatment, resulting in insufficient oxygenation of the YBCO superconducting phase (Y123) and a significant reduction in critical current density ( J c ) 19 . Extrusion molding then emerged as an alternative approach for the fabrication of YBCO wires 20-25 . In this technique, YBCO powder is mixed with an organic additive system to form a plastic paste, which is then pressed into shape through specialized molds. Although this method avoids the structural damage caused by cold working, it suffers from the decomposition and volatilization of organic additives during subsequent heat treatment which lead to the formation of pores and cracks within the green body, significantly reducing the densification and mechanical strength of the wire; Moreover, due to the geometric constraints of round-wire architectures, conventional processing techniques are ineffective in controlling grain orientation, thereby failing to form textured structures with a-b plane alignment—an essential prerequisite for achieving high superconducting performance. Later efforts explored techniques such as directional solidification 26 , zone melting 27 , electrospinning 28 , and electrophoretic deposition 29 . However, these methods remained limited in their ability to produce long-length wires. Direct-ink-writing (DIW) 3D printing technology has achieved significant progress in the fabrication of YBCO bulk materials. Studies have demonstrated that epoxy resin infiltration of 3D-printed bulks can effectively enhance their mechanical strength 30 , while subsequent top-seeded melt-textured growth (TSMTG) processing for single crystallization leads to a remarkable improvement in the superconducting performance of YBCO bulk 31 . However, the application of this technique to the fabrication of YBCO round wires still faces critical challenges. On the one hand, the geometric constraints of round-wire structures make it difficult to effectively control the grain orientation uniformity of YBCO; on the other hand, the limited solid content of the ink (typically 30–60 wt.%) leads to insufficient sintering densification 32 , generating numerous pores that severely impede current transport, thereby limiting the superconducting performance. DIW-based bimaterial 3D printing is an advanced additive manufacturing technique that integrates two materials for coordinated fabrication 33 and was initially developed for applications in biological cell research 34 . In recent years, this technology has advanced significantly, enabling more complex material combinations such as liquid metal–polymer 35 , polymer–ceramic 36 , polymer–polymer 37 , and functional ceramic systems 38 . Early researchers attempted to co-extrude YBCO rods with Cu/Ag composite cladding using direct extrusion technology 39 . Although this experiment failed to achieve the desired structure or performance, it provided some valuable insights. In this paper, we present an innovative strategy for the controlled fabrication of Ag-core/YBCO-shell composite superconducting wires, based on DIW bimaterial 3D printing technology. Through continuous and synchronized dual-slurry flow control combined with computational fluid dynamics (CFD)-optimized core-shell nozzle design, we achieved precise structural formation of the composite filaments. The as-printed precursor filaments, after freeze-drying treatment, develop radial pores in the YBCO layer, which serve as rapid transport channels for Ag⁺ during high-temperature co-sintering. As Ag⁺ rapidly diffused along these pores, a fraction selectively substituted Cu 2+ at the Cu(1) sites in Y123 phase, forming a transition phase YBa 2 Cu 3 Ag x Cu 3-x O 7-δ (Ag x ) with a preferred [001] orientation. This transition phase established coherent interfaces with Y123, and the resulting templating effect induced the growth of subsequently formed Y123 grains with [001] ( c -axis) alignment, establishing a unique solid-solution-driven texturing mechanism. Additionally, the incorporation of Ag promoted grain bridging into interconnected network structures, thereby enhancing the superconducting performance of the composite wire. Meanwhile, the Ag core functions as a mechanical support framework that effectively redistributes external stresses, leading to significantly improved tensile and bending resistance. Our work not only provides a strategy to overcome the intrinsic brittleness of YBCO and achieve crystallographic texturing in round-wire geometries, but also offers broad applicability to other materials with structural growth patterns. Fabrication of Ag-core YBCO superconducting wires via DIW bimaterial 3D printing The DIW bimaterial process for fabricating Ag-core YBCO wires involves precursor powders synthesis, ink formulation, 3D printing, freeze-drying, and sintering in an oxygen atmosphere 40 (Supplementary Fig.1). We designed two distinct ink systems (aqueous and oil-based), each combined with YBCO precursor powder and nano-Ag particles, to produce four printable ink formulations (Methods). Rheological analysis (Supplementary Information, section 1 and Supplementary Fig.2) revealed that the aqueous ink, exhibiting gel-like behavior, was more suitable for forming the supporting shell structure 41 , while the oil-based ink demonstrated superior sol-state fluidity conducive to pore infiltration 42 , making it ideal as the core material in bimaterial 3D printing. Nozzle selection directly governs print quality and material properties (Supplementary Information, section 2 and Supplementary Fig.3). The 16+22G configuration was chosen after evaluating its YBCO/Ag dimensional outcomes (Supplementary Table 1). Microstructural evolution of aqueous YBCO inks during prolonged sintering at various temperatures was characterized by scanning electron microscopy (SEM) (Supplementary Information, section 3 and Supplementary Fig.4), complemented by thermogravimetric-derivative thermogravimetric analysis (TG-DTG) (Supplementary Information, section 4 and Supplementary Fig.5). These characterizations enabled the optimization of post-processing sintering protocols (Supplementary Fig.6), successfully reducing the total processing time from 300 hours (required for TSMTG) 43 and even longer durations for conventional methods 44 to merely 50 hours—achieving over 80% reduction in processing time. The choice of drying method is critical for preserving the structural integrity of the printed geometry and regulating the interaction between the core and shell materials during sintering. In this paper, freeze-drying was adopted, as the resulting aligned pores facilitate atomic diffusion and oxygen incorporation during subsequent high-temperature sintering (Supplementary Information, section 5 and Supplementary Fig.7). We employed the ANSYS-Polyflow 45 module to perform CFD simulations for optimizing the feed angle of the bimaterial printing nozzle. This modification resolved the issue of extruded filaments curling or warping toward one side at the outer feed port, which was caused by gravity-induced horizontal feeding and uneven pressure distribution within the internal cavity (Supplementary Fig.8). The fluid model adopted the Herschel-Bulkley model 46 (Supplementary Fig.9 and Supplementary Table 2), which accurately simulated the laminar flow behavior of aqueous YBCO ink in the outer channel of the nozzle (Supplementary Figs.10-14). After adjusting the inlet orientation upward by 45°, the internal pressure within the nozzle was alleviated, the velocity mismatch between the two inks was reduced, and the curling of the printed filaments was eliminated (Supplementary Information, section 6 and Supplementary Fig.15). The oil-based Ag ink and the aqueous YBCO ink are fed from the inner and outer inlets of a CFD-optimized coaxial nozzle, which is integrated with a mechanically controlled DIW 3D printing system to fabricate Ag/YBCO core-shell precursor filaments (Methods, Fig.1a and Supplementary Fig.16). A subsequent freezing step results in the radial growth of ice crystals within the aqueous YBCO shell (Fig1b), leaving behind aligned pores after drying. These aligned pores facilitate the diffusion of Ag + ions during high-temperature sintering, enabling atomic migration into adjacent Y123 grains (Fig.1c). This process leads to the formation of Ag x solid solution phase. The coherent interface between this solid solution and Y123 generates a templating effect that promotes subsequent growth of [001]-oriented Y123 grains (Fig.1d). Using this approach, we fabricated Ag-core YBCO round wires along various predefined trajectories, including linear, zigzag, spirals, and concentric paths (Fig.2a and Supplementary Video 1). Cross-sectional SEM characterization of the superconducting wire (Fig.2b-d) reveals distinct elemental distribution between the YBCO shell and the Ag core. Energy-dispersive X-ray spectroscopy (EDS) quantification yields an atomic composition ratio of Y:Ba:Cu ≈ 1:2:3 (Supplementary Table 3), consistent with the stoichiometry of the Y123 phase. To determine whether the structure is orthorhombic or tetragonal, we performed X-ray diffraction (XRD) analysis (Fig.2e). The calculated lattice parameters from the XRD pattern show minimal deviation compared with literature values (Supplementary Table 4), further confirming the formation of the superconducting Y123 phase with an orthorhombic structure. Surface morphological characterization by SEM confirmed that the obtained superconducting wire has a diameter of approximately 600 μm (Fig.2f). Microstructural examination showed distinct Ag particle exudation on the wire surface (Fig.2g), with elemental distribution confirmed through EDS mapping (Fig.2h-l). Three-dimensional surface morphology analysis of the superconducting wire was conducted using extended-depth confocal microscopy (Supplementary Fig.17a,b). The average surface depth variation was measured to be 4.01 μm, with 91.15% of pore depths measuring less than 10 μm (Supplementary Fig.17c), indicating excellent surface flatness. Building on this methodology, we also fabricated YBCO-core/Ag-shell superconducting wires via freeze-drying process, utilizing aqueous Ag ink and oil-based YBCO ink (Supplementary section 7, Supplementary Figs.18 and 19). The Ag shell encasing the YBCO core displays a compact, cellular microstructure, free of porosity or void-type defects (Supplementary Fig.19e,f). In contrast, hollow pure Ag wires subjected to the same sintering conditions reveal a streamlined grain morphology accompanied by numerous fine surface pores (Supplementary Fig.19g,h). Owing to the higher Ag content relative to Y123, the XRD pattern exhibits stronger diffraction peaks for Ag and weaker peaks for Y123 (Supplementary Fig.19i). The interaction mechanism between Ag and YBCO played a crucial role in promoting nucleation, regulating growth, and suppressing defects. We conducted further investigations into additional characteristics of the interfacial effects. Microstructural characterization of Y123/ YBa 2 Ag x Cu 3-x O 7-δ coherent interfaces The doping mechanism of Ag in the YBCO system remains controversial in academia, primarily focusing on whether Ag exists as grain boundary precipitates or forms a solid solution by substituting atoms in the YBCO lattice 47-50 . In this section, we reveal the coexistence of two Ag incorporation mechanisms through microstructural characterization, providing a more comprehensive understanding of its doping behavior. The Ag-core YBCO superconducting wire was embedded in epoxy resin for sample preparation to facilitate grinding and polishing. The outer YBCO particles were observed to form interconnected structures (Fig.3a,b), whereas in both solid-core (SC-YBCO) and hollow-core (HC-YBCO) 3D-printed pure YBCO wires (Supplementary Fig.20), the particles remained discretely distributed with significantly lower packing density compared to the interface-modified YBCO. This observation confirms the previously reported mechanism whereby the segregation of a small amount of Ag particles at grain boundaries facilitates the bridging of superconducting grains 49 . The interface between YBCO and Ag exhibits excellent densification after high-temperature co-sintering, forming a continuous and uniform bonding state free of voids, cracks, or porosity defects (Fig.3c). Five potential phases may exist in the YBCO-Ag system (Supplementary Table 5). Among these, the Ag x phase is particularly difficult to distinguish from the Y123 matrix using SEM-EDS or XRD techniques, due to their nearly identical lattice parameters and elemental composition 47 . Electron probe microanalysis (EPMA) was conducted at the interface region near YBCO (Fig.3d). Point analysis at location A1 revealed an atomic composition of Y 7.76 Ba 15.10 Ag 1.07 Cu 22.25 O 53.82 (at. %). The combined atomic percentage of Ag and Cu (23.32 at. %) is exactly three times the Y content (7.76 at. %), consistent with the nominal stoichiometry of YBa 2 Ag x Cu 3-x O 7-δ ( x ≈ 0.14). Additionally, Ag x phase with x ≈ 0.19 was detected at point A2 (Supplementary Table 6). This phase ( x ≈ 0.17) was also observed in the YBCO region adjacent to the interface in the Ag-coated YBCO wire (Supplementary Fig.21b). Backscattered electron (BSE) imaging did not exhibit significant contrast between the Ag x and Y123 phases due to their limited difference in average atomic number (Δ Z ). BSE imaging typically requires Δ Z > 0.1 Z (where Z is the average atomic number of the matrix phase) to produce detectable contrast 51 . In the case of Y123 ( Z = 22.62) and Ag x ( Z = 22.62 + 1.38 x ), this condition is satisfied only when x > 1.64, at which point the Δ Z exceeds the threshold for reliable contrast discrimination. Zhang et al. 50 synthesized Ag x via solid-state reaction and conducted EDS analysis on large grains (5~10 μm), concluding that x max is only 0.023. Nevertheless, subsequent studies have reported higher Ag solubility 47,52 , which may be attributed to the influence of Ag doping on the thermodynamic behavior of the YBCO system. The introduction of Ag significantly lowers the peritectic reaction temperature of YBCO 53 , and optimizing sintering conditions (e.g., reducing sintering temperature or adjusting oxygen partial pressure) can effectively enhance Ag solubility in the YBCO lattice. Atomic-scale characterization of the Ag x phase was conducted using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The analysis revealed a distinct incoherent interface between Ag x (112) and Ag (Fig.3e). When the specimen was tilted to align the electron beam along the [110] zone axis of Ag (Supplementary Fig.22), well-defined (111) lattice fringes of Ag were clearly resolved while the Ag x phase exhibited diffuse contrast, providing direct evidence of their incoherent relationship. Uniform elemental distribution throughout the Agₓ phase was verified by STEM-EDS (Supplementary Fig.23). Atomic-resolution HAADF-STEM identified coherent Ag x /Y123 interface (Fig.3f-h), with nanoscale STEM-EDS mapping showing localized distribution of Ag, while Y, Ba, Cu, and O were uniformly dispersed across the entire region, confirming the phase distribution of Ag x and Y123 as well as their interfacial positions. Figure 3i reveals the atomic-scale characteristics at the Ag x /Y123 phase interface. In the Ag x phase, Ag + preferentially substitutes for Cu 2+ in the unit cell through two possible configurations (Supplementary Fig.24a): Cu(1) site replacement in CuO chains (Mode 1) versus Cu(2) site substitution in CuO 2 planes (Mode 2). Assuming x = 0.25, we demonstrate one possible unit cell structure with Mode 1 substitution (Supplementary Fig.24b) and the unique configuration for Mode 2 (Supplementary Fig.24c). To highlight the atomic site occupancy of Ag in the Y123 unit cell, the distribution of oxygen vacancies was neglected, as detailed in the work of Behera et al. 47 The chain-structured Cu(1) sites exhibit greater structural tolerance, allowing local distortion to accommodate the larger ionic radius of Ag + . Furthermore, while Cu(2) maintains a stable 2+ charge state, Cu(1) can adopt variable charges including 1+, with charge imbalance compensated by oxygen vacancies, explaining the preferential substitution at Cu(1) sites 47 . The unit cells of Mode 1 Ag x and Y123 were rotated to align with the atomic features on both sides of the interface. In HAADF images, atomic sites with higher atomic numbers appear brighter and more distinct. Consequently, the brightest upper and lower atomic rows in the Y123 region correspond to the Ba-O layers. In the Ag x region, the substitution of Cu 2+ by Ag + enhances the atomic-site brightness of the CuO chain layer. Atomic-resolution analysis confirms a continuous transition at the Ag x /Y123 interface, where the Ba-O layers of Y123 maintain perfect alignment with the CuO chains of Ag x without dislocations or atomic displacements, providing definitive evidence of their coherent relationship. Fast Fourier transform (FFT) processing of the high-resolution TEM (HRTEM) image (Fig.3j) generated two distinct diffraction patterns (Fig.3k). Detailed inverse FFT processing and IFFT live profiles (Supplementary Fig.25) confirmed lattice spacings of 2.319 Å for Y123(041) and 2.335 Å for Ag x (014), demonstrating their near-parallel alignment ( θ ≈ 2°) (Fig.3l). A misfit dislocation is observed at the interfacial region between lattice fringes, resulting from localized lattice distortions induced by Ag⁺ substitution. Figure 3m reveals two bright spot arrays and one vacancy, demonstrating atomic ordering at the coherent Y123(041)/Ag x (014) interface. The lattice misfit ( δ ) can be evaluated by the following formula 54 : The minimal δ confirms near-perfect phase coherence with low interfacial energy and continuous atomic arrangement, forming a seamless transition interface. In contrast, Ag x /Y211 exhibits incoherent interfacial characteristics (Supplementary Information, section 8 and Supplementary Fig.26). Crystallographic orientation and superconducting properties Our experimental confirmation of the formation of Ag x substitutional solid solution has raised important questions regarding its influence on the crystallographic orientation and grain size of the Y123 superconducting phase, as well as the underlying mechanisms of these effects. To elucidate these aspects, we use electron backscatter diffraction (EBSD) analysis of the YBCO layer in wire cross-sections to specifically investigate the role of coherent Ag x /Y123 interfaces in controlling crystallographic alignment and grain orientation during microstructural development. The Ag x phase was predominantly distributed along both sides of the radial channels formed after freeze-drying (Fig.4a,b). Within the selected region, the phase fraction of Ag x was measured at 3.5%, with an additional 4% Y211 phase also detected (Fig.4c). The sample coordinate system is illustrated in Fig.4d. To preserve structural integrity during grinding/polishing and meet conductivity requirements, specimens were first embedded in graphene aerogel before epoxy resin infiltration and curing. In the coordinate system, the RD aligns with the radial axis of the wire's cross-section, the TD is perpendicular to the radial direction, and the ND corresponds to the longitudinal axis of the wire. In the inverse pole figure (IPF) for the RD direction (Fig.4e), the red regions (Fig.4h) representing the [001] orientation ( c -axis) dominate and are widely distributed, indicating a pronounced c -axis texture along the RD. In contrast, the IPF map for the TD direction (Fig.4f) shows no significant orientation preference, which results from its perpendicular alignment to the radial direction. The ND-direction IPF (Fig.4g) exhibits extensive distribution of blue and green regions corresponding to [100] and [010] orientations ( a - and b -axes), demonstrating predominant a-b plane alignment along the ND. The pole figure (PF) of the {001} ( a-b plane) of the Y123 phase shows that the poles are concentrated along the RD direction (Fig.4i), further indicating that the normal direction of the {001} planes is parallel to the RD. This suggests that the a–b planes of the Y123 grains are preferentially oriented along the longitudinal direction of the superconducting wire, forming a texture. An isolated analysis of Ag x grain orientations (Supplementary Fig27a,b) revealed a remarkable alignment with Y123 textures. In contrast, Y 2 BaCuO 5 (Y211), serving solely as a secondary phase, exhibited conventional flux-pinning behavior without distinct grain orientation characteristics 55 (Supplementary Fig.27c,d). The kernel average misorientation (KAM) map (Supplementary Fig.28) indicates that 99.4% of grains exhibit KAM values below 2°, suggesting remarkably low internal strain accumulation during the 3D printing, freeze-drying, and high-temperature co-sintering processes. The average grain size of Y123 was measured to be 1.12 μm (Supplementary Fig.29), significantly smaller than the 1.73 μm observed in SC-YBCO (Supplementary Fig.30a), demonstrating effective grain refinement through process optimization. Under identical sample coordinates, the triaxial IPF maps of the SC-YBCO wire cross-section reveal randomly distributed crystallographic orientations (Supplementary Fig.30b-h). The PF shows disordered distributions of {100}, {010}, and {001} poles (Supplementary Fig.30i). This non-preferential orientation behavior stands in sharp contrast to the strong texturing observed in Ag-core YBCO composite wires. We performed magnetization measurements with the magnetic field perpendicular to the wires (H∥ c -axis) to evaluate the superconductivity of SC-YBCO, Ag-core YBCO and Ag-coated YBCO wires, including T c and J c . The Ag-core YBCO wire exhibited a T c of 90 K under zero-field-cooled (ZFC) conditions (Fig.4j). Both SC-YBCO and Ag-coated YBCO showed comparable T c values of 91 K and 90 K respectively (Supplementary Fig.31a,d). Figure 4k, Supplementary Fig.31b,e present the magnetization curves of the three wire types. The Ag-composite YBCO exhibits significantly higher magnetization than SC-YBCO. The width of the perpendicular magnetization hysteresis loops ( ∆M ) correlates with J c , which was analyzed along the wire axis using the extended Bean model 31,56 (Supplementary Information, section 9 and Supplementary Fig.32): Where with R 1 and R 2 being the inner and outer radii of the YBCO layer, respectively. The linear M–H response observed in 3D-printed pure Ag at 10 K (Supplementary Fig.33) confirms that the superconductivity of the composite wire arises exclusively from the YBCO shell. Moreover, we developed a generalized J c calculation model applicable to both SC-YBCO and Ag-coated YBCO wires (Supplementary Information, section 9 and Supplementary Fig.34). The model-derived J c values of Ag-core YBCO at various temperatures (Fig.4l) indicate a value of 1.73×10 4 A·cm −2 at 10 K, surpassing that of SC-YBCO (4.45×10 3 A·cm −2 at 10 K; Supplementary Fig.31c), representing a 3.9-fold enhancement (Supplementary Fig.35a). This enhancement is consistent with previous studies, indicating that the addition of Ag into YBCO does not compromise its superconducting properties. On the contrary, it markedly enhances J c by strengthening flux pinning effects 57,58 . Notably, the J c of Ag-core YBCO is comparable to Ag-coated YBCO (1.68×10 4 A·cm −2 at 10 K; Supplementary Fig.31f and Fig.35b), though the latter exhibits faster J c degradation under increasing magnetic fields (Supplementary Fig.35c). When the applied field is aligned parallel to either the c -axis or a-b planes, Ag-core YBCO wires demonstrate pronounced anisotropic behavior, consistent with the characteristics of directionally solidified samples reported in the literature 59 . To ensure the critical current ( I c ) measurement fidelity during cryogenic conditions, the Ag-core YBCO wire surfaces were protected by magnetron-sputtered copper layers (10 μm thick, Supplementary Fig.36a) that simultaneously provided excellent electrical contact and thermal stabilization. The sample was cooled to 26 K in a custom-designed Dewar system. Due to spatial constraints within the Dewar, a ~5 cm-long copper-plated wire segment was selected and fabricated into the test device structure shown in Supplementary Fig.36b. Using a four-probe measurement system, reliable I c s were obtained (Fig.4m). Three independent tests yielded I c values of 25.45, 21.86, and 23.31 A, corresponding to J c of 1.27×10⁴ ,1.09×10⁴, and 1.16×10⁴ A·cm⁻², respectively. These results confirm the current-carrying capacity of Ag-core YBCO composite wires under low-temperature conditions. Mechanical characterization of YBCO superconducting wire Figure 5a presents the stress-strain curves of Ag-core YBCO superconducting wires under tensile testing at room temperature (RT) and 77 K. Compared to RT, the superconducting wires exhibit a significantly higher elastic modulus at 77 K. The stress reaches its peak value (25.16 MPa) at 0.25% of strain at 77 K, followed by abrupt fracture, characteristic of typical brittle failure. At temperature of RT, after reaching the maximum stress (22.26 MPa), the curve displays a small stress plateau during the descending phase, indicating that the plastic deformation capability of the Ag core partially alleviates brittle fracture, resulting in fracture strain of 1.25%. Fractographic analysis at RT (Fig.5b) shows a smooth fracture surface in the YBCO layer, dimpled ductile fracture in the Ag core, and a 5~10 μm wide plastic bonding zone at their interface 60 . Three-point bending tests were conducted on Ag-core YBCO wires and 3D-printed YBCO (3DP-YBCO) bulk samples (5 × 5 × 45 mm 3 ) with a span length of 30 mm (Supplementary section 10). The resulting stress-strain curves of both samples at RT and 77 K (Fig.5c) reveal fundamentally distinct mechanical behaviors between Ag-core YBCO wires and 3DP-YBCO bulk materials. The Ag-core YBCO wires exhibit pronounced plastic deformation characteristics under both temperatures. At RT, they demonstrate typical elastoplastic response with a yield strength ( σ b ) of 19.26 MPa and fracture strain of 4.30%. At 77 K, cryogenic hardening elevates σ b to 33.28 MPa while maintaining 1.0% plastic deformation capability. In stark contrast, the 3DP-YBCO bulk displays characteristic brittle fracture behavior achieving fracture strength of 1.96 MPa (at 2.68% of strain) at RT and the strength of 8.86 MPa at 77 K, but with strain capacity drastically reduced to 0.027%. This behavioral dichotomy demonstrates that the Ag-core architecture enhances fracture energy of YBCO from 52.2 MJ·m -3 (bulk) to 1361.8 MJ·m -3 (wire) at RT which is a 26-fold improvement. The enhancement becomes even more remarkable at 77 K (209-fold), where the bulk material shows only 2.4 MJ·m -3 compared to the wire's 502 MJ·m -3 (Fig.5d). Consistent with literature reports, the incorporation of Ag markedly improves the mechanical properties of the YBCO system, particularly in terms of fracture toughness and bending strength 53,61 . The detailed mechanical parameters obtained from tensile and three-point bending tests are summarized in Supplementary Table 7. The three-point bending fractography further reveals dimple structures in the Ag core at RT (Fig.5e). Supplementary Video 2 demonstrates the dynamic response of the superconducting wire during loading through in situ SEM three-point bending tests. SEM characterization (Fig.5f,g) indicates that the toughening effect of the Ag-core structure alters the crack propagation mode in YBCO from intergranular to transgranular fracture. Cracks propagate through YBCO grains, creating straight and sharp fracture surfaces 62 (Supplementary Fig.37a-c). In contrast, cracks in 3DP-YBCO bulk preferentially propagate along weakly bonded grain boundaries, forming rough intergranular fracture surfaces that reflect the tortuous crack path around grains (Supplementary Fig.37d-f). Micro-Vickers hardness testing of Ag-core YBCO superconducting wires under varying indentation loads (Fig.5h, Supplementary Fig.38 and Supplementary Table 8) reveals a distinct hardness gradient: YBCO exhibits the highest hardness, followed by the Ag/YBCO interface, with the pure Ag core showing the lowest values. Nanoindentation tests conducted at different penetration depths (400, 800, and 1200 nm; Supplementary Fig.39) demonstrate an anomalous mechanical response which displays higher hardness in Ag core and elastic modulus than both YBCO and the interface region at all tested depths. Discussion and outlook In early studies on YBCO superconducting round wires, the four-probe J c measurement employed a relatively short voltage lead spacing (~4 mm) 22 . This experimental configuration may lead to an overestimation of J c due to insufficient voltage drop measurement region. Notably, neither Ponnusamy et al. 23 nor Grader et al. 24 explicitly reported the test temperature for J c in their studies. The absence of this critical parameter hinders a meaningful cross-comparison with our research findings. Although Ponnusamy et al. 23 reported a 140 cm-long YBCO superconducting wire, their graphical data reveal multiple discontinuities along the sample. The researchers presumably employed methods such as soldering or foil wrapping to reconnect these breaks; however, they provide no detailed description of these procedures. Most remarkably, they achieved a YBCO wire with a remarkably small diameter of just 1.6 mm yet exhibiting an exceptional bending fracture strength of 170 MPa 23 . In contrast, the TSMTG sample (3 × 4 × 18 mm 3 ) exhibited a bending fracture strength of merely 104 MPa 63 , potentially attributable to the higher density of their wire fabrication. In this paper, we investigated a controllable fabrication strategy for YBCO superconducting round wires, enabling continuous and uninterrupted 3D printing at the meter-length scales while maintaining high superconductivity after sintering. The Ag-core/YBCO-shell long-wire configuration exhibits significant structural advantages for power transmission applications. This coaxial composite design enables spatial separation of mechanical and electrical functionalities: the Ag core, owing to its excellent ductility and electrical conductivity, serves as both structural support and current shunt following a local quench, whereas the outer YBCO shell, with its superior superconducting properties, functions as the primary current-carrying channel. In addition, we have systematically revealed the interfacial effects in the Ag-YBCO system across multiple scales. The freeze-drying process creates a radial porous structure within the YBCO shell, which provides effective diffusion pathways for the outward migration of Ag particles during high-temperature heat treatment. This distinctive diffusion behavior significantly modulates the microstructure of YBCO grains through interfacial composite effects, ultimately achieving synergistic enhancement of the material's overall performance. The introduction of Ag cores facilitates the formation of Y123 superconducting grains, leading to synchronized enhancement in both J c and mechanical properties primarily through three mechanisms: (i) It promotes a bridging effect among superconducting grains, leading to the formation of interconnected network structures. This enables observable current transport behavior at low temperatures through direct transport measurements, rather than relying solely on J c values inferred from magnetic measurements. (ii) It forms a solid solution Ag x through lattice substitution, which regulates the grain orientation of Y123. Ag partially substitutes into the Y123 crystal lattice, forming an Agₓ phase with a [001] orientation. Due to the coherent interfacial relationship between the Agₓ phase and the Y123 lattice, this orientation feature can induce subsequent Y123 grain growth along the [001] direction, thereby facilitating the texturing of the superconducting round wire. Unlike conventional TSMTG, in this study, the texturing is intrinsically driven by the solid solution, eliminating the need for seed crystals. (iii) It affects the mechanical behavior of the grains between Ag and Y123. We found that the significant improvement in tensile and bending performance originates from a shift in the crack propagation mechanism—from intergranular to transgranular fracture. The ductile fracture characteristics of the Ag core are transmitted to the YBCO shell, resulting in a visible plastic plateau in the stress–strain curve. In summary, we designed and developed a bimaterial 3D printing platform featuring both low pressure difference and low flow rate difference. Through systematic investigation of the rheological properties of the dual-ink system, we achieved the high-efficiency 3D printing of Ag-core/YBCO-shell round wires with diameters below 1 mm and lengths exceeding 1 meter. Four-probe transport measurements on long sample achieved 1.27 × 10 4 A·cm -2 at 26 K, whereas 3D-printed pure YBCO wires failed to achieve current transport due to particle dispersion. Three-point bending tests showed a fracture energy reached 1361.8 MJ·m -3 at room temperature, which is 26 times higher than that of the bulk sample (52.2 MJ·m -3 ). We confirmed the existence of a substitute doping mechanism of Ag in the YBCO system and elucidated the synergistic optimization mechanism of Ag doping on both the superconductivities and mechanical properties of YBCO. Our findings provide a direct experimental explanation for the long-standing question of "Ag doping enhancing YBCO performance while the underlying mechanism remained unclear" in the research community. Furthermore, this core/shell structure is inherently compatible with multifilamentary cable designs, facilitating the construction of high-current-capacity superconducting cable systems. Methods Ink Preparation YBCO precursor powder synthesis: Y 2 O 3 (99.99%, Macklin), CuO (99.5%, Macklin), and BaCO 3 (99.95%, Macklin) were mixed in a stoichiometric molar ratio (Y: Ba: Cu = 1:2:3) with anhydrous ethanol and ball-milled using a planetary mill (MSK-SFM-1). The mixture was then dried at 90°C for 12 h in an oven to obtain YBCO precursor powder. Aqueous binder solution formulation: sodium carboxymethyl cellulose (CMC, [C 6 H 7 O 2 (OH) 2 OCH 2 COONa] n ; viscosity: 600-1000 mPa·s; Macklin) was dissolved in deionized water at 6.5 wt.% under mechanical stirring for 2 h to serve as the binder. Oil-based binder solution formulation: ethyl cellulose (EC, (C 12 H 22 O 5 ) n ; viscosity: 300 mPa·s; Macklin) was dissolved in diethylene glycol monobutyl ether (C 8 H 18 O 3 , 99%, Macklin) at 5 wt.%, under mechanical stirring for 2 h at 60°C in a water bath. 3D Printing ink preparation for Ag-core YBCO wires: The aqueous YBCO ink was prepared by mixing 50 g YBCO precursor powder with 15 mL of an aqueous binder solution, followed by the addition of 5 g Epoxidized soybean oil (ESO, C 57 H 98 O 18 , Aladdin) and homogenization through roller milling (3 cycles). The commercial Ag/Pd paste (Sryed Paste) was used directly as the oil-based Ag ink. 3D printing ink preparation for Ag-coated YBCO wires: The aqueous Ag ink was formulated blending 50 g of Ag nanoparticles (200 nm, 99.99%, Macklin) with 30 mL of an aqueous binder solution and 6 g of ESO, followed by roller milling for 3 cycles. The oil-based YBCO ink was prepared by combining 50 g of YBCO precursor powder with 20 mL oil-based binder solution and 4 g of glycerol (C 3 H 8 O 3 , 99%, Macklin), then homogenized via roller milling (3 cycles). Fabrication of YBCO Superconducting Wires via Bimaterial DIW 3D Printing The oil-based ink was loaded into a modified DIW 3D printer (Bio-Architect PRO, Regenovo, China) through the inner feed port of the nozzle, with pneumatic extrusion controlled at a pressure of 0.15 MPa. Simultaneously, the aqueous ink was delivered via an external syringe pump connected to the outer feed port of the optimized printing nozzle, maintaining a flow rate of 1.0 mL/min. The robotic arm was programmed to move along the X/Y axes at a speed of 2.0 mm/s during deposition (Supplementary Video 1). Printed samples were immediately cryo-cast at -80°C for 24 h, followed by freeze-drying to obtain green wires. These wire precursors were subsequently annealed in a tube furnace under an oxygen atmosphere using the thermal profile shown in Supplementary Fig.6 to finalize the YBCO superconducting wires. Material and structure characterization X-ray diffraction (XRD) analysis was performed using an X' Pert PRO MPD diffractometer (PANalytical, Netherlands) with Cu Kα radiation over a 2 θ range of 5°–90°. Microstructural characterization was conducted using field-emission scanning electron microscopy (FE-SEM, Apreo S, Thermo Fisher Scientific, USA) equipped with energy-dispersive X-ray spectroscopy (EDS, Octane Pro, AMETEK, USA) for elemental mapping at a working distance of 10 mm and accelerating voltage of 15 kV. Transmission electron microscopy (TEM, Talos F200s, Thermo Fisher Scientific, USA) coupled with a Super-X EDS system (Bruker, Germany) was employed for nanoscale compositional analysis. Crystallographic orientation analysis was performed via electron backscatter diffraction (EBSD, Symmetry S2, Oxford Instruments, UK) operating at 20 kV with a step size of 50 nm and acquisition rate exceeding 300 points per second (pps). Thermogravimetric analysis (TGA) was carried out using a simultaneous TGA/differential scanning calorimetry (DSC) analyzer (TGA/SDTA 851e, Mettler-Toledo, Switzerland) from 25°C to 1000°C at a heating rate of 2°C min -1 under nitrogen atmosphere. Measurements Rheological properties were measured using a rotational rheometer (MCR302, Anton Paar, UK) at 25°C, performing both steady-state shear (0.01-100 s -1 ) and dynamic oscillatory tests (1 Hz, 0.01-3000 Pa). Superconducting properties were characterized by SQUID magnetometry (MPMSR2, Quantum Design, USA), including zero-field-cooled (ZFC, 50 Oe) magnetization curves and temperature-dependent hysteresis loops (10, 35, 55, and 77 K, ±70 kOe). Electrical transport measurements were conducted via the four-point probe method (SMS600C-H-4Q current source, Cryogenic, UK) at 26 K to determine critical current ( I c ). Copper coatings were deposited by magnetron sputtering (Mantis Deposition, UK) using a 99.999% pure copper target (Kurt J. Lesker, USA) under 5×10 -6 Torr base pressure, with 100 W RF power and 3 mTorr argon working pressure, resulting in 10 μm-thick coatings. Mechanical characterization included: in situ SEM three-point bending tests (Quanta 650 FEG SEM, FEI, USA with Deben Microtest 5kN module, UK), tensile tests (UTM4104, China), and conventional three-point bending (20 mm span, 0.1 mm/min loading rate). Hardness was evaluated using micro-Vickers (FM-700, Future-Tech, Japan) and nanoindentation (TI-950, Hysitron, USA with Berkovich diamond tip). All mechanical tests were performed at both room temperature and 77 K (custom liquid nitrogen Dewar). Declarations Acknowledgments: We thank Huadong Yong, Zhiwei Zhang and Yajun Zhang, Lanzhou University for enlightening discussions. We also appreciate Yihao Li, Chuanguang Liu, Jihua Deng, and Yunfan Shi for their assistance in the four-probe measurements at low temperatures. Funding: National Key Research and Development Program of China grant 2024YFB4607300 National Natural Science Funds for Distinguished Young Scholar grant 12325205 Distinguished Talent Research Funding of Lanzhou grant 127000-563225112 Science and Technology Leading Talent Project of Gansu Province grant 24RCKB008 Author contributions: F. Y. Z and B. Q. Z. contributed equally to this work. X. Y. Z., B. Q. Z. developed the concept. X. Y. Z., B. Q. Z., F. Y. Z., X. Y. S. and Y. T. Z. designed the overall experiments. F. Y. Z and X. Y. S. conducted the computational predictions and simulation analysis. F. Y. Z designed the 3D printing experiment and write original draft. F. Y. Z. and, Y. T. 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DateS3.xlsx Theoretical d-spacings (Å) of Y2BaCuO5 corresponding to different (hkl) planes (PDF Card - 01-079-0238). supplementarymaterialsNM.docx supplementary_materials-NM VideoS1.mp4 Fabrication of Ag-core YBCO precursor filaments via bimaterial DIW 3D printing. VideoS2.mp4 In situ SEM three-point bending mechanical response of superconducting wires. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7301425","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":502842269,"identity":"0c1d6e90-ae84-41ec-af8f-363b0641402e","order_by":0,"name":"Xingyi Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA90lEQVRIiWNgGAWjYDACCTjJ2PjgAZiTQLyWZoMEErSAAZsEUVrkZzc/e/i1zSJPPiK5rSLhz2EGfvYcA4afO3BrYZxzzNxY5oxEseGNxLYbCTyHGSR73hgw9p7BrYVZIsFMWqJCInHjDJAWicMMBjdyDJgZ23BrYZNI/yYtYQDRUpBgcJjBnpAWHokcM8kPQFvmSyS2MSQkAG2RIKBFQiKnTJrhjETiBp6HzRIJB9J5JM48KzjYi0eL/Iz0bZI/2+oS57enP/zw4Y+1HH978sYHP/FoAQcBD5AwuJAAcSmIOIBfAzCgf4Cs6yeobhSMglEwCkYqAAB9CFA+Ytt0PwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-2856-170X","institution":"Lanzhou University","correspondingAuthor":true,"prefix":"","firstName":"Xingyi","middleName":"","lastName":"Zhang","suffix":""},{"id":502842270,"identity":"f806f095-2995-456e-9210-e53c472613b5","order_by":1,"name":"Fenyan Zhao","email":"","orcid":"","institution":"Lanzhou University","correspondingAuthor":false,"prefix":"","firstName":"Fenyan","middleName":"","lastName":"Zhao","suffix":""},{"id":502842271,"identity":"5f169726-2dda-4597-9f8b-fc910a22f426","order_by":2,"name":"Baoqiang Zhang","email":"","orcid":"","institution":"Lanzhou University","correspondingAuthor":false,"prefix":"","firstName":"Baoqiang","middleName":"","lastName":"Zhang","suffix":""},{"id":502842272,"identity":"20f13fec-0eea-45cc-aadd-6a513983b08b","order_by":3,"name":"Xiyang Su","email":"","orcid":"","institution":"The Hong Kong University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Xiyang","middleName":"","lastName":"Su","suffix":""},{"id":502842273,"identity":"90dbf3cb-861f-4798-8772-2175481ecab0","order_by":4,"name":"Yantang Zhao","email":"","orcid":"","institution":"Lanzhou University","correspondingAuthor":false,"prefix":"","firstName":"Yantang","middleName":"","lastName":"Zhao","suffix":""},{"id":502842274,"identity":"dafdef5e-aac3-4d74-b860-29f4713edb89","order_by":5,"name":"You-He Zhou","email":"","orcid":"","institution":"Lanzhou University","correspondingAuthor":false,"prefix":"","firstName":"You-He","middleName":"","lastName":"Zhou","suffix":""}],"badges":[],"createdAt":"2025-08-05 14:02:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7301425/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7301425/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":89530149,"identity":"f0e93a79-ef47-4663-ba00-b62cde1b1420","added_by":"auto","created_at":"2025-08-21 03:43:11","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":221837,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProcess schematic: DIW bimaterial 3D printing and post-processing of Ag-core YBCO superconducting wires, with mechanism illustration. a,\u003c/strong\u003e A core–shell structured Ag-core YBCO precursor filament was fabricated via DIW bimaterial 3D printing. The oil-based Ag ink was fed through the inner inlet of the coaxial nozzle, while the aqueous YBCO ink was introduced through the outer inlet. CFD simulations were employed to optimize nozzle design by adjusting the feed angle (\u003cem\u003eθ\u003c/em\u003e) (Supplementary section 6), aiming to mitigate ink extrusion curling issues. \u003cstrong\u003eb,\u003c/strong\u003e After printing, the precursor filament is subjected to freeze-drying. During the freezing stage, ice crystals within the aqueous YBCO shell grow preferentially along the radial direction. Following sublimation, the resulting oriented porous structure provides rapid diffusion channels for Ag\u003csup\u003e+\u003c/sup\u003e during the subsequent high-temperature sintering process. \u003cstrong\u003ec,\u003c/strong\u003e During sintering, the Ag core and YBCO shell—with closely matched thermal expansion coefficients—enable Ag\u003csup\u003e+\u003c/sup\u003e to diffuse through the channels, where it substitutes Cu(1) sites in adjacent Y123 unit cells\u003csup\u003e47\u003c/sup\u003e, forming the Ag\u003csub\u003ex\u003c/sub\u003e phase. \u003cstrong\u003ed,\u003c/strong\u003e The [001]-oriented Ag\u003csub\u003ex\u003c/sub\u003e phase establishes a coherent interface with Y123, inducing a templating effect that promotes the growth of subsequent superconducting grains along the [001] direction, simultaneously enhancing mechanical integrity and preserving superior superconducting properties.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/0faa56b428caf0632a3f2d65.png"},{"id":89530151,"identity":"673f6be1-a14b-4e42-9639-e4d908835588","added_by":"auto","created_at":"2025-08-21 03:43:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":352638,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMacroscopic and microscopic characterization of Ag-core YBCO superconducting wires. a,\u003c/strong\u003e Superconducting wires printed in straight lines (~10 cm), zigzag patterns (~40 cm), and concentric paths (~160 cm) (Methods and SupplementaryVideo 1).\u003cstrong\u003e b,\u003c/strong\u003e Cross-sectional secondary electron (SE) image of the superconducting wire demonstrates excellent interfacial bonding between the YBCO shell and Ag core, with no observable cracks.\u003cstrong\u003e c,d, \u003c/strong\u003eEDS elemental mapping of Ag, Y, Ba, Cu, and O on the cross-section, showing their localized distributions.\u003cstrong\u003e e,\u003c/strong\u003e XRD pattern of the superconducting wire, with calculated lattice parameters confirming the formation of the orthorhombic Y123 superconducting phase (Supplementary Table 3). \u003cstrong\u003ef,\u003c/strong\u003e SE image of the wire's exterior morphology, with measured diameter of approximately 600 μm.\u003cstrong\u003e g, \u003c/strong\u003eAg particles were observed on the YBCO outer surface. \u003cstrong\u003eh-l, \u003c/strong\u003eElemental EDS mapping of Ag, Y, Ba, Cu, and O on the outer surface confirms that Ag particles partially diffused to the surface of the superconducting wire via the oriented channels generated during freeze-drying.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/f7f61675a081fd0ad02be9ea.png"},{"id":89530152,"identity":"252cbc93-68b0-48a2-8403-91b4a985227d","added_by":"auto","created_at":"2025-08-21 03:43:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":491439,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterization of YBCO-Ag interface structure. a,\u003c/strong\u003e SE images of the polished cross-section of Ag-core YBCO superconducting wire. \u003cstrong\u003eb, \u003c/strong\u003eAn interconnected grain structure is observed in the YBCO region.\u003cstrong\u003e c, \u003c/strong\u003eSE image of the YBCO-Ag interface region, showing a highly dense bonding without defects such as voids, cracks, or pores, exhibiting a continuous and uniform interfacial structure. \u003cstrong\u003ed, \u003c/strong\u003eBSE image of EPMA point analysis at the edge region of the YBCO side. The elemental composition at point A1 is Y\u003csub\u003e7.76\u003c/sub\u003eBa\u003csub\u003e15.10\u003c/sub\u003eAg\u003csub\u003e1.07\u003c/sub\u003eCu\u003csub\u003e22.25\u003c/sub\u003eO\u003csub\u003e53.82\u003c/sub\u003e (at. %), consistent with the nominal composition of the Ag\u003csub\u003ex\u003c/sub\u003e phase (\u003cem\u003ex\u003c/em\u003e ≈ 0.14). The Ag\u003csub\u003ex\u003c/sub\u003e phase (\u003cem\u003ex\u003c/em\u003e ≈ 0.19) is also detected at point A2 (Supplementary Table 6). \u003cstrong\u003ee,\u003c/strong\u003e HAADF image of incoherent interface between Ag\u003csub\u003ex\u003c/sub\u003e and Ag, with FFT pattern inset (lower right). \u003cstrong\u003ef,\u003c/strong\u003e HAADF image showing coherent interface between Ag\u003csub\u003ex\u003c/sub\u003e and Y123.\u003cstrong\u003e g,h,\u003c/strong\u003e STEM-EDS mapping of Ag, Y, Ba, Cu, and O. The localized distribution of Ag reveals the phase segregation between Ag\u003csub\u003ex\u003c/sub\u003e and Y123, as well as the interfacial boundary.\u003cstrong\u003e i,\u003c/strong\u003e HAADF image revealing atomic features at the Ag\u003csub\u003ex\u003c/sub\u003e/Y123 phase interface. \u003cstrong\u003ej, \u003c/strong\u003eHRTEM image of the interfacial region. \u003cstrong\u003ek, \u003c/strong\u003eCorresponding FFT pattern.\u003cstrong\u003e l,\u003c/strong\u003e IFFT reconstruction.\u003cstrong\u003e m,\u003c/strong\u003e Atomic arrangement at coherent interface between Ag\u003csub\u003ex\u003c/sub\u003e(014) and Y123(041) planes.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/eb7b92462944955508afac09.png"},{"id":89530155,"identity":"7e1dc61e-28cb-4c37-90d1-65d6d43f94a8","added_by":"auto","created_at":"2025-08-21 03:43:11","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":438535,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGrain orientation analysis and superconducting properties of Ag-core YBCO wire. a, \u003c/strong\u003eYBCO band contrast map. Radial porosity distribution was clearly observed in the YBCO microstructure. \u003cstrong\u003eb,\u003c/strong\u003e Phase distribution mapping. The Ag\u003csub\u003ex\u003c/sub\u003e phase was preferentially distributed along both sides of the radial pores. \u003cstrong\u003ec,\u003c/strong\u003e Associated color legend with phase fractions.\u003cstrong\u003e d, \u003c/strong\u003eSample geometry and coordinate system schematic.\u003cstrong\u003e e,\u003c/strong\u003e RD-IPF orientation mapping. A pronounced [001] orientation was identified along the RD.\u003cstrong\u003e f,\u003c/strong\u003e TD-IPF orientation mapping.\u003cstrong\u003e g, \u003c/strong\u003eND-IPF orientation mapping, pronounced [010] and [100] orientations were identified along the RD. \u0026nbsp;\u003cstrong\u003eh,\u003c/strong\u003e IPF color coding reference.\u003cstrong\u003e i, \u003c/strong\u003eY123-PF. The {001} planes are aligned along the RD, indicating that the normal direction of the {001} planes is parallel to the RD. \u003cstrong\u003ej, \u003c/strong\u003eTemperature dependence of magnetic susceptibility with \u003cem\u003eT\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e = 90 K.\u003cstrong\u003e k, \u003c/strong\u003eMagnetization hysteresis characteristics. \u003cstrong\u003el,\u003c/strong\u003e Temperature-dependent \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e from extended Bean model analysis (Supplementary section 9), reaching 1.74×10\u003csup\u003e4\u003c/sup\u003e A·cm\u003csup\u003e-2\u003c/sup\u003e at 10 K. \u003cstrong\u003em,\u003c/strong\u003e \u003cem\u003eI-V\u003c/em\u003e curve of \u003cem\u003eI\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e measurement for superconducting wire at 26 K using four-probe method (Supplementary Fig.34), with three independent test results: 25.45, 21.88, and 23.31 A.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/1b765fcf26489434aa7c9873.png"},{"id":89530153,"identity":"e8261b07-cc00-40da-bec2-bb625358125d","added_by":"auto","created_at":"2025-08-21 03:43:11","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":347660,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMechanical characterization of Ag-core YBCO superconducting wires. a,\u0026nbsp;\u003c/strong\u003eStress-strain curves of composite superconducting wire from tensile tests at RT and 77 K. \u003cstrong\u003eb,\u0026nbsp;\u003c/strong\u003eSEM fractography of tensile specimens showing: smooth fracture surface in YBCO layer, ductile dimple structures in Ag core, and 5-10 μm plastic bonding zone at interface\u003csup\u003e60\u003c/sup\u003e. \u003cstrong\u003ec,\u003c/strong\u003e\u0026nbsp;Stress-strain curves from three-point bending tests of Ag-core YBCO superconducting wire and 3DP-YBCO bulk (5×5×45 mm\u003csup\u003e3\u003c/sup\u003e) at RT and 77 K. \u003cstrong\u003ed,\u003c/strong\u003e\u0026nbsp;Mechanical property comparison of two structures: Yield strength (\u003cem\u003ex\u003c/em\u003e-axis) versus flexural fracture energy (left \u003cem\u003ey\u003c/em\u003e-axis) and static toughness (right \u003cem\u003ey\u003c/em\u003e-axis).\u003cstrong\u003e e,\u0026nbsp;\u003c/strong\u003eFracture morphology of three-point bending specimens. \u003cstrong\u003ef,g, \u003c/strong\u003eIn situ SEM observations of transgranular crack propagation during bending. \u003cstrong\u003eh,\u003c/strong\u003e\u0026nbsp;Micro-Vickers hardness comparison across different regions of the Ag-core YBCO wire: YBCO shows the highest hardness, followed by the Ag/YBCO interface, while the pure Ag core exhibits the lowest hardness.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/f1ce5941f3dc5b038e05c01c.png"},{"id":91810880,"identity":"f4f4b8cb-0b1c-43ac-9c32-3b9a7297e53b","added_by":"auto","created_at":"2025-09-22 04:33:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2991007,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/09559bc0-1180-45ec-814a-3e588eb13975.pdf"},{"id":89530150,"identity":"809d1e5b-38c8-4ade-aaaa-e0ff1718ee8e","added_by":"auto","created_at":"2025-08-21 03:43:11","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":15526,"visible":true,"origin":"","legend":"\u003cp\u003eTheoretical d-spacings (Å) of YBa2Cu3O7-δ corresponding to different (hkl) planes (PDF Card - 00-038-1433).\u003c/p\u003e","description":"","filename":"DateS1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/914861a32f9b960022de735b.xlsx"},{"id":89530148,"identity":"0d314c5c-e9cc-42c2-b8ea-5bd0a20c6d75","added_by":"auto","created_at":"2025-08-21 03:43:11","extension":"xlsx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":18296,"visible":true,"origin":"","legend":"\u003cp\u003eTheoretical d-spacings (Å) of YBa2AgxCu3-xO7-δ corresponding to different (hkl) planes (PDF Card - 04-006-3247).\u003c/p\u003e","description":"","filename":"DateS2.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/f70f5643fef5bcac4c313a92.xlsx"},{"id":89530636,"identity":"a0120be8-9a45-46b3-a879-84191aafd2cb","added_by":"auto","created_at":"2025-08-21 03:51:11","extension":"xlsx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":18521,"visible":true,"origin":"","legend":"\u003cp\u003eTheoretical d-spacings (Å) of Y2BaCuO5 corresponding to different (hkl) planes (PDF Card - 01-079-0238).\u003c/p\u003e","description":"","filename":"DateS3.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/859159f6ec68c0e6e9fc5674.xlsx"},{"id":89530157,"identity":"60bb9ad5-a336-48c1-a86b-e710c008a129","added_by":"auto","created_at":"2025-08-21 03:43:12","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":22230869,"visible":true,"origin":"","legend":"supplementary_materials-NM","description":"","filename":"supplementarymaterialsNM.docx","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/308552fb48bb55eb3884026a.docx"},{"id":89530158,"identity":"dc1056e4-660b-4303-93e9-a0b1b5607248","added_by":"auto","created_at":"2025-08-21 03:43:12","extension":"mp4","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":40790760,"visible":true,"origin":"","legend":"Fabrication of Ag-core YBCO precursor filaments via bimaterial DIW 3D printing.","description":"","filename":"VideoS1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/3192055926c69583c652a5e8.mp4"},{"id":89530159,"identity":"83632463-9e37-472e-a809-eae8dd4caf9f","added_by":"auto","created_at":"2025-08-21 03:43:12","extension":"mp4","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":43839274,"visible":true,"origin":"","legend":"In situ SEM three-point bending mechanical response of superconducting wires.","description":"","filename":"VideoS2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7301425/v1/2c36c3174b4350c2e19213a4.mp4"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eAg/YBCO superconducting round wires fabricated by bimaterial 3D printing\u003c/p\u003e","fulltext":[{"header":"Main Text","content":"\u003cp\u003eThe industrial-scale production of Nb\u003csub\u003e3\u003c/sub\u003eSn/Cu and NbTi/Cu composite wires with diverse cross-sectional geometries, including their cable-in-conduit conductor (CICC) forms, has advanced low-temperature superconducting applications\u003csup\u003e1\u003c/sup\u003e. However, their use in high-field magnets remains constrained by high cooling costs and low irreversibility fields\u003csup\u003e2,3\u003c/sup\u003e. Since the discovery of YBCO superconductors with a critical temperature (\u003cem\u003eT\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e) above the boiling point of liquid nitrogen (77 K) in the late 1980s\u003csup\u003e4,5\u003c/sup\u003e, nearly four decades of research and development have led to the establishment of a diversified application system for this material. YBCO bulk superconductors demonstrate significant application potential in high-power fields such as magnetic levitation systems and high-field permanent magnets\u003csup\u003e6\u003c/sup\u003e. In low-power applications, epitaxial YBCO thin films, owing to their exceptional superconducting properties, are widely employed in advanced devices such as superconducting quantum interference devices (SQUIDs) and superconducting filters\u003csup\u003e7\u003c/sup\u003e. Meanwhile, second-generation (2G) high-temperature superconducting (HTS) tapes, based on coated conductor technology, have emerged as key materials for power cables and ultra-high-filed superconducting magnet\u003csup\u003e8,9\u003c/sup\u003e. For applications of YBCO in the power sector and large-scale magnet systems, the most promising structural form is long-length round wire\u003csup\u003e10,11\u003c/sup\u003e, the realization of which relies on the controlled fabrication of high-performance superconducting wires. However, the fundamental challenge lies in the ceramic nature of YBCO, which exhibits intrinsic brittleness that complicates wire fabrication and handling\u003csup\u003e12\u003c/sup\u003e.\u0026nbsp;Structurally, the YBCO unit cell consists of layered stacks (sequentially: CuO chains, Ba-O layers, CuO\u003csub\u003e2\u003c/sub\u003e planes, Y layers, CuO\u003csub\u003e2\u003c/sub\u003e planes, and Ba-O layers), with superconductivity primarily originating from electron transport within the CuO\u003csub\u003e2\u003c/sub\u003e planes (\u003cem\u003ea-b\u003c/em\u003e planes)\u003csup\u003e13,14\u003c/sup\u003e. This necessitates well-controlled crystallographic texturing to achieve high superconductivity. Due to this structural peculiarity, it has remained challenging to realize an engineering wire architecture for YBCO analogous to the round-wire composite structure used in Nb\u003csub\u003e3\u003c/sub\u003eSn/Cu conductors\u003csup\u003e15\u003c/sup\u003e,\u0026nbsp;which is essential for integration into cable and magnet systems.\u003c/p\u003e\n\u003cp\u003eAs early as the 1990s, researchers attempted various methods to fabricate YBCO superconducting round wires. Among them, the powder-in-tube (PIT) method emerged as a representative technique, in which YBCO superconducting powder was encapsulated in Ag or Cu tubes, followed by cold working processes such as drawing or forging\u003csup\u003e16,17\u003c/sup\u003e. However, the intrinsic brittleness of YBCO ceramics led to severe grain structure damage during cold deformation\u003csup\u003e18\u003c/sup\u003e. Although post-annealing was employed for structural recovery, the dense metallic sheath hindered oxygen diffusion during heat treatment, resulting in insufficient oxygenation of the YBCO superconducting phase (Y123) and a significant reduction in critical current density (\u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e)\u003csup\u003e19\u003c/sup\u003e. Extrusion molding then emerged as an alternative approach for the fabrication of YBCO wires\u003csup\u003e20-25\u003c/sup\u003e. In this technique, YBCO powder is mixed with an organic additive system to form a plastic paste, which is then pressed into shape through specialized molds. Although this method avoids the structural damage caused by cold working, it suffers from the decomposition and volatilization of organic additives during subsequent heat treatment which lead to the formation of pores and cracks within the green body, significantly reducing the densification and mechanical strength of the wire; Moreover, due to the geometric constraints of round-wire architectures, conventional processing techniques are ineffective in controlling grain orientation, thereby failing to form textured structures with \u003cem\u003ea-b\u003c/em\u003e plane alignment\u0026mdash;an essential prerequisite for achieving high superconducting performance. Later efforts explored techniques such as directional solidification\u003csup\u003e26\u003c/sup\u003e, zone melting\u003csup\u003e27\u003c/sup\u003e, electrospinning\u003csup\u003e28\u003c/sup\u003e, and electrophoretic deposition\u003csup\u003e29\u003c/sup\u003e. However, these methods remained limited in their ability to produce long-length wires.\u003c/p\u003e\n\u003cp\u003eDirect-ink-writing (DIW) 3D printing technology has achieved significant progress in the fabrication of YBCO bulk materials. Studies have demonstrated that epoxy resin infiltration of 3D-printed bulks can effectively enhance their mechanical strength\u003csup\u003e30\u003c/sup\u003e, while subsequent top-seeded melt-textured growth (TSMTG) processing for single crystallization leads to a remarkable improvement in the superconducting performance of YBCO bulk\u003csup\u003e31\u003c/sup\u003e. However, the application of\u0026nbsp;this technique to the fabrication of YBCO round wires still faces critical challenges. On the one hand, the geometric constraints of round-wire structures make it difficult to effectively control the grain orientation uniformity of YBCO; on the other hand, the limited solid content of the ink (typically 30\u0026ndash;60 wt.%) leads to insufficient sintering densification\u003csup\u003e32\u003c/sup\u003e, generating numerous pores that severely impede current transport, thereby limiting the superconducting performance. DIW-based bimaterial 3D printing\u0026nbsp;is an advanced additive manufacturing technique that integrates two materials for coordinated fabrication\u003csup\u003e33\u003c/sup\u003e and was initially developed for applications in biological cell research\u003csup\u003e34\u003c/sup\u003e. In recent years, this technology has advanced significantly, enabling more complex material combinations such as liquid metal\u0026ndash;polymer\u003csup\u003e35\u003c/sup\u003e, polymer\u0026ndash;ceramic\u003csup\u003e36\u003c/sup\u003e, polymer\u0026ndash;polymer\u003csup\u003e37\u003c/sup\u003e, and functional ceramic systems\u003csup\u003e38\u003c/sup\u003e.\u0026nbsp;Early researchers attempted to co-extrude YBCO rods with Cu/Ag composite cladding using direct extrusion technology\u003csup\u003e39\u003c/sup\u003e. Although this experiment failed to achieve the desired structure or performance, it provided some valuable insights.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn this paper, we present an innovative strategy for the controlled fabrication of Ag-core/YBCO-shell composite superconducting wires, based on DIW bimaterial 3D printing technology.\u0026nbsp;Through continuous and synchronized dual-slurry flow control combined with computational fluid dynamics (CFD)-optimized core-shell nozzle design, we achieved precise structural formation of the composite filaments. The as-printed precursor filaments, after freeze-drying treatment, develop radial pores in the YBCO layer, which serve as rapid transport channels for Ag⁺ during high-temperature co-sintering. As Ag⁺ rapidly diffused along these pores, a fraction selectively substituted Cu\u003csup\u003e2+\u003c/sup\u003e at the Cu(1) sites in Y123 phase, forming a transition phase YBa\u003csub\u003e2\u003c/sub\u003eCu\u003csub\u003e3\u003c/sub\u003eAg\u003csub\u003ex\u003c/sub\u003eCu\u003csub\u003e3-x\u003c/sub\u003eO\u003csub\u003e7-\u0026delta;\u003c/sub\u003e (Ag\u003csub\u003ex\u003c/sub\u003e) with a preferred [001] orientation. This transition phase established coherent interfaces with Y123, and the resulting templating effect induced the growth of subsequently formed Y123 grains with [001] (\u003cem\u003ec\u003c/em\u003e-axis) alignment,\u0026nbsp;establishing a unique solid-solution-driven texturing mechanism. Additionally, the incorporation of Ag promoted grain bridging into interconnected network structures, thereby enhancing the superconducting performance of the composite wire. Meanwhile, the Ag core functions as a mechanical support framework that effectively redistributes external stresses, leading to significantly improved tensile and bending resistance. Our work not only provides a strategy to overcome the intrinsic brittleness of YBCO and achieve crystallographic texturing in round-wire geometries, but also offers broad applicability to other materials with structural growth patterns.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFabrication of Ag-core YBCO superconducting wires via DIW bimaterial 3D printing\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe DIW bimaterial process for fabricating Ag-core YBCO wires involves precursor powders synthesis, ink formulation, 3D printing, freeze-drying, and sintering in an oxygen atmosphere\u003csup\u003e40\u003c/sup\u003e (Supplementary Fig.1).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eWe designed two distinct ink systems (aqueous and oil-based), each combined with YBCO precursor powder and nano-Ag particles, to produce four printable ink formulations (Methods). Rheological analysis (Supplementary Information, section 1 and Supplementary Fig.2) revealed that the aqueous ink, exhibiting gel-like behavior, was more suitable for forming the supporting shell structure\u003csup\u003e41\u003c/sup\u003e, while the oil-based ink demonstrated superior sol-state fluidity conducive to pore infiltration\u003csup\u003e42\u003c/sup\u003e, making it ideal as the core material in bimaterial 3D printing. Nozzle selection directly governs print quality and material properties (Supplementary Information, section 2 and Supplementary Fig.3). The 16+22G configuration was chosen after evaluating its YBCO/Ag dimensional outcomes (Supplementary Table 1).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eMicrostructural evolution of aqueous YBCO inks during prolonged sintering at various temperatures was characterized by scanning electron microscopy (SEM) (Supplementary Information, section 3 and\u0026nbsp;Supplementary Fig.4), complemented by thermogravimetric-derivative thermogravimetric analysis (TG-DTG) (Supplementary Information, section 4 and Supplementary Fig.5). These characterizations enabled the optimization of post-processing sintering protocols (Supplementary Fig.6), successfully reducing the total processing time from 300 hours (required for TSMTG)\u003csup\u003e43\u003c/sup\u003e and even longer durations for conventional methods\u003csup\u003e44\u003c/sup\u003e to merely 50 hours\u0026mdash;achieving over 80% reduction in processing time.\u0026nbsp;The choice of drying method is critical for preserving the structural integrity of the printed geometry and regulating the interaction between the core and shell materials during sintering.\u0026nbsp;In this paper, freeze-drying was adopted, as the resulting aligned pores facilitate atomic diffusion and oxygen incorporation during subsequent high-temperature sintering (Supplementary Information, section 5 and Supplementary Fig.7).\u003c/p\u003e\n\u003cp\u003eWe employed the ANSYS-Polyflow\u003csup\u003e45\u003c/sup\u003e module to perform CFD simulations for optimizing the feed angle of the bimaterial printing nozzle. This modification resolved the issue of extruded filaments curling or warping toward one side at the outer feed port, which was caused by gravity-induced horizontal feeding and uneven pressure distribution within the internal cavity (Supplementary Fig.8). The fluid model adopted the Herschel-Bulkley model\u003csup\u003e46\u003c/sup\u003e (Supplementary Fig.9 and Supplementary Table 2), which accurately simulated the laminar flow behavior of aqueous YBCO ink in the outer channel of the nozzle (Supplementary Figs.10-14). After adjusting the inlet orientation upward by 45\u0026deg;, the internal pressure within the nozzle was alleviated, the velocity mismatch between the two inks was reduced, and the curling of the printed filaments was eliminated (Supplementary Information, section 6 and Supplementary Fig.15).\u003c/p\u003e\n\u003cp\u003eThe oil-based Ag ink and the aqueous YBCO ink are fed from the inner and outer inlets of a CFD-optimized coaxial nozzle,\u0026nbsp;which is integrated with a mechanically controlled DIW 3D printing system to fabricate Ag/YBCO core-shell precursor filaments (Methods, Fig.1a and Supplementary Fig.16). A subsequent freezing step results in the radial growth of ice crystals within the aqueous YBCO shell (Fig1b), leaving behind aligned pores after drying.\u0026nbsp;These aligned pores facilitate the diffusion of Ag\u003csup\u003e+\u003c/sup\u003e ions during high-temperature sintering, enabling atomic migration into adjacent Y123 grains (Fig.1c). This process leads to the formation of Ag\u003csub\u003ex\u003c/sub\u003e solid solution phase. \u0026nbsp;The coherent interface between this solid solution and Y123 generates a templating effect that promotes subsequent growth of [001]-oriented Y123 grains (Fig.1d). Using this approach, we fabricated Ag-core YBCO round wires along various predefined trajectories, including linear, zigzag, spirals, and concentric paths (Fig.2a and Supplementary Video 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCross-sectional SEM characterization of the superconducting wire (Fig.2b-d) reveals distinct elemental distribution between the YBCO shell and the Ag core. Energy-dispersive X-ray spectroscopy (EDS) quantification yields an atomic composition ratio of Y:Ba:Cu \u0026asymp; 1:2:3 (Supplementary Table 3), consistent with the stoichiometry of the Y123 phase. To determine whether the structure is orthorhombic or tetragonal, we performed X-ray diffraction (XRD) analysis (Fig.2e). The calculated lattice parameters from the XRD pattern show minimal deviation compared with literature values (Supplementary Table 4), further confirming the formation of the superconducting Y123 phase with an orthorhombic structure. Surface morphological characterization by SEM confirmed that the obtained superconducting wire has a diameter of approximately 600 \u0026mu;m (Fig.2f). Microstructural examination showed distinct Ag particle exudation on the wire surface\u0026nbsp;(Fig.2g), with elemental distribution confirmed through EDS mapping (Fig.2h-l). Three-dimensional surface morphology analysis of the superconducting wire was conducted using extended-depth confocal microscopy (Supplementary Fig.17a,b). The average surface depth variation was measured to be 4.01 \u0026mu;m, with 91.15% of pore depths measuring less than 10 \u0026mu;m (Supplementary Fig.17c), indicating excellent surface flatness.\u003c/p\u003e\n\u003cp\u003eBuilding on this methodology, we also fabricated YBCO-core/Ag-shell superconducting wires via freeze-drying process, utilizing aqueous Ag ink and oil-based YBCO ink (Supplementary section 7, Supplementary Figs.18 and 19).\u0026nbsp;The Ag shell encasing the YBCO core displays a compact, cellular microstructure, free of porosity or void-type defects (Supplementary Fig.19e,f).\u0026nbsp;In contrast, hollow pure Ag wires subjected to the same sintering conditions reveal a streamlined grain morphology accompanied by numerous fine surface pores (Supplementary Fig.19g,h).\u0026nbsp;Owing to the higher Ag content relative to Y123, the XRD pattern exhibits stronger diffraction peaks for Ag and weaker peaks for Y123 (Supplementary Fig.19i).\u0026nbsp;The interaction mechanism between Ag and YBCO played a crucial role in promoting nucleation, regulating growth, and suppressing defects. We conducted further investigations into additional characteristics of the interfacial effects.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;Microstructural characterization of Y123/\u003c/strong\u003e \u003cstrong\u003eYBa\u003csub\u003e2\u003c/sub\u003eAg\u003csub\u003ex\u003c/sub\u003eCu\u003csub\u003e3-x\u003c/sub\u003eO\u003csub\u003e7-\u0026delta;\u003c/sub\u003e coherent interfaces\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe doping mechanism of Ag in the YBCO system remains controversial in academia, primarily focusing on whether Ag exists as grain boundary precipitates or forms a solid solution by substituting atoms in the YBCO lattice\u003csup\u003e47-50\u003c/sup\u003e. \u0026nbsp;In this section, we reveal the coexistence of two Ag incorporation mechanisms through microstructural characterization, providing a more comprehensive understanding of its doping behavior.\u003c/p\u003e\n\u003cp\u003eThe Ag-core YBCO superconducting wire was embedded in epoxy resin for sample preparation to facilitate grinding and polishing. The outer YBCO particles were observed to form interconnected structures (Fig.3a,b), whereas in both solid-core (SC-YBCO) and hollow-core (HC-YBCO) 3D-printed pure YBCO wires (Supplementary Fig.20), the particles remained discretely distributed with significantly lower packing density compared to the interface-modified YBCO. This observation confirms the previously reported mechanism whereby the segregation of a small amount of Ag particles at grain boundaries facilitates the bridging of superconducting grains\u003csup\u003e49\u003c/sup\u003e.\u0026nbsp;The interface between YBCO and Ag exhibits excellent densification after high-temperature co-sintering, forming a continuous and uniform bonding state free of voids, cracks, or porosity defects\u0026nbsp;(Fig.3c).\u0026nbsp;Five potential phases may exist in the YBCO-Ag system (Supplementary Table 5). Among these, the Ag\u003csub\u003ex\u003c/sub\u003e phase is particularly difficult to distinguish from the Y123 matrix using SEM-EDS or XRD techniques, due to their nearly identical lattice parameters and elemental composition\u003csup\u003e47\u003c/sup\u003e. Electron probe microanalysis (EPMA) was conducted at the interface region near YBCO (Fig.3d). Point analysis at location A1 revealed an atomic composition of Y\u003csub\u003e7.76\u003c/sub\u003eBa\u003csub\u003e15.10\u003c/sub\u003eAg\u003csub\u003e1.07\u003c/sub\u003eCu\u003csub\u003e22.25\u003c/sub\u003eO\u003csub\u003e53.82\u003c/sub\u003e (at. %). The combined atomic percentage of Ag and Cu (23.32 at. %) is exactly three times the Y content (7.76 at. %), consistent with the nominal stoichiometry of YBa\u003csub\u003e2\u003c/sub\u003eAg\u003csub\u003ex\u003c/sub\u003eCu\u003csub\u003e3-x\u003c/sub\u003eO\u003csub\u003e7-\u0026delta;\u003c/sub\u003e (\u003cem\u003ex\u003c/em\u003e \u0026asymp; 0.14). Additionally, Ag\u003csub\u003ex\u003c/sub\u003e phase with \u003cem\u003ex\u003c/em\u003e \u0026asymp; 0.19 was detected at point A2 (Supplementary Table 6). This phase (\u003cem\u003ex\u003c/em\u003e \u0026asymp; 0.17) was also observed in the YBCO region adjacent to the interface in the Ag-coated YBCO wire (Supplementary Fig.21b). Backscattered electron (BSE) imaging did not exhibit significant contrast between the Ag\u003csub\u003ex\u003c/sub\u003e and Y123 phases due to their limited difference in average atomic number (\u0026Delta;\u003cem\u003eZ\u003c/em\u003e). BSE imaging typically requires \u0026Delta;\u003cem\u003eZ\u003c/em\u003e \u0026gt; 0.1\u003cem\u003eZ\u003c/em\u003e (where \u003cem\u003eZ\u0026nbsp;\u003c/em\u003eis the average atomic number of the matrix phase) to produce detectable contrast\u003csup\u003e51\u003c/sup\u003e. In the case of Y123 (\u003cem\u003eZ\u003c/em\u003e = 22.62) and Ag\u003csub\u003ex\u003c/sub\u003e (\u003cem\u003eZ\u003c/em\u003e = 22.62 + 1.38\u003cem\u003ex\u003c/em\u003e), this condition is satisfied only when\u003cem\u003e\u0026nbsp;x\u003c/em\u003e \u0026gt; 1.64, at which point the\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u0026Delta;\u003cem\u003eZ\u003c/em\u003e exceeds the threshold for reliable contrast discrimination.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eZhang et al.\u003csup\u003e50\u003c/sup\u003e synthesized Ag\u003csub\u003ex\u003c/sub\u003e via solid-state reaction and conducted EDS analysis on large grains (5~10 \u0026mu;m), concluding that \u003cem\u003ex\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e is only 0.023. Nevertheless, subsequent studies have reported higher Ag solubility\u003csup\u003e47,52\u003c/sup\u003e, which may be attributed to the influence of Ag doping on the thermodynamic behavior of the YBCO system. The introduction of Ag significantly lowers the peritectic reaction temperature of YBCO\u003csup\u003e53\u003c/sup\u003e, and optimizing sintering conditions (e.g., reducing sintering temperature or adjusting oxygen partial pressure) can effectively enhance Ag solubility in the YBCO lattice.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eAtomic-scale characterization of the Ag\u003csub\u003ex\u003c/sub\u003e phase was conducted using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The analysis revealed a distinct incoherent interface between Ag\u003csub\u003ex\u003c/sub\u003e(112) and Ag (Fig.3e). When the specimen was tilted to align the electron beam along the [110] zone axis of Ag (Supplementary Fig.22), well-defined (111) lattice fringes of Ag were clearly resolved while the Ag\u003csub\u003ex\u003c/sub\u003e phase exhibited diffuse contrast, providing direct evidence of their incoherent relationship.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eUniform elemental distribution throughout the Agₓ phase was verified by STEM-EDS (Supplementary Fig.23). Atomic-resolution HAADF-STEM identified coherent Ag\u003csub\u003ex\u003c/sub\u003e/Y123 interface (Fig.3f-h), with nanoscale STEM-EDS mapping showing localized distribution of Ag, while Y, Ba, Cu, and O were uniformly dispersed across the entire region, confirming the phase distribution of Ag\u003csub\u003ex\u003c/sub\u003e and Y123 as well as their interfacial positions.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eFigure 3i reveals the atomic-scale characteristics at the Ag\u003csub\u003ex\u003c/sub\u003e/Y123 phase interface. In the Ag\u003csub\u003ex\u003c/sub\u003e phase, Ag\u003csup\u003e+\u003c/sup\u003e preferentially substitutes for Cu\u003csup\u003e2+\u003c/sup\u003e in the unit cell through two possible configurations (Supplementary Fig.24a): Cu(1) site replacement in CuO chains (Mode 1) versus Cu(2) site substitution in CuO\u003csub\u003e2\u003c/sub\u003e planes (Mode 2). Assuming \u003cem\u003ex\u003c/em\u003e = 0.25, we demonstrate one possible unit cell structure with Mode 1 substitution (Supplementary Fig.24b) and the unique configuration for Mode 2 (Supplementary Fig.24c). To highlight the atomic site occupancy of Ag in the Y123 unit cell, the distribution of oxygen vacancies was neglected, as detailed in the work of Behera et al.\u003csup\u003e47\u003c/sup\u003e The chain-structured Cu(1) sites exhibit greater structural tolerance, allowing local distortion to accommodate the larger ionic radius of Ag\u003csup\u003e+\u003c/sup\u003e. Furthermore, while Cu(2) maintains a stable 2+ charge state, Cu(1) can adopt variable charges including 1+, with charge imbalance compensated by oxygen vacancies, explaining the preferential substitution at Cu(1) sites\u003csup\u003e47\u003c/sup\u003e. The unit cells of Mode 1 Ag\u003csub\u003ex\u003c/sub\u003e and Y123 were rotated to align with the atomic features on both sides of the interface. In HAADF images, atomic sites with higher atomic numbers appear brighter and more distinct. Consequently, the brightest upper and lower atomic rows in the Y123 region correspond to the Ba-O layers. In the Ag\u003csub\u003ex\u003c/sub\u003e region, the substitution of Cu\u003csup\u003e2+\u003c/sup\u003e by Ag\u003csup\u003e+\u003c/sup\u003e enhances the atomic-site brightness of the CuO chain layer.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eAtomic-resolution analysis confirms a continuous transition at the Ag\u003csub\u003ex\u003c/sub\u003e/Y123 interface, where the Ba-O layers of Y123 maintain perfect alignment with the CuO chains of Ag\u003csub\u003ex\u003c/sub\u003e without dislocations or atomic displacements, providing definitive evidence of their coherent relationship. Fast Fourier transform (FFT) processing of the high-resolution TEM (HRTEM) image (Fig.3j) generated two distinct diffraction patterns (Fig.3k). Detailed inverse FFT processing and IFFT live profiles (Supplementary Fig.25) confirmed lattice spacings of 2.319 \u0026Aring; for Y123(041) and 2.335 \u0026Aring; for Ag\u003csub\u003ex\u003c/sub\u003e(014), demonstrating their near-parallel alignment (\u003cem\u003e\u0026theta;\u003c/em\u003e \u0026asymp; 2\u0026deg;) (Fig.3l). A misfit dislocation is observed at the interfacial region between lattice fringes, resulting from localized lattice distortions induced by Ag⁺ substitution. Figure 3m reveals two bright spot arrays and one vacancy, demonstrating atomic ordering at the coherent Y123(041)/Ag\u003csub\u003ex\u003c/sub\u003e(014) interface. The lattice misfit (\u003cem\u003e\u0026delta;\u003c/em\u003e) can be evaluated by the following formula\u003csup\u003e54\u003c/sup\u003e:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"388\" height=\"33\"\u003e\u003c/p\u003e\n\u003cp\u003eThe minimal \u003cem\u003e\u0026delta;\u003c/em\u003e confirms near-perfect phase coherence with low interfacial energy and continuous atomic arrangement, forming a seamless transition interface. In contrast, Ag\u003csub\u003ex\u003c/sub\u003e/Y211 exhibits incoherent interfacial characteristics (Supplementary Information, section 8 and Supplementary Fig.26).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCrystallographic orientation and superconducting properties\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOur experimental confirmation of the formation of Ag\u003csub\u003ex\u003c/sub\u003e substitutional solid solution has raised important questions regarding its influence on the crystallographic orientation and grain size of the Y123 superconducting phase, as well as the underlying mechanisms of these effects. To elucidate these aspects, we use electron backscatter diffraction (EBSD) analysis of the YBCO layer in wire cross-sections to specifically investigate the role of coherent Ag\u003csub\u003ex\u003c/sub\u003e/Y123 interfaces in controlling crystallographic alignment and grain orientation during microstructural development.\u003c/p\u003e\n\u003cp\u003eThe Ag\u003csub\u003ex\u003c/sub\u003e phase was predominantly distributed along both sides of the radial channels formed after freeze-drying (Fig.4a,b). Within the selected region, the phase fraction of Ag\u003csub\u003ex\u003c/sub\u003e was measured at 3.5%, with an additional 4% Y211 phase also detected (Fig.4c). The sample coordinate system is illustrated in Fig.4d. To preserve structural integrity during grinding/polishing and meet conductivity requirements, specimens were first embedded in graphene aerogel before epoxy resin infiltration and curing. In the coordinate system, the RD aligns with the radial axis of the wire\u0026apos;s cross-section, the TD is perpendicular to the radial direction, and the ND corresponds to the longitudinal axis of the wire. In the inverse pole figure (IPF) for the RD direction (Fig.4e), the red regions (Fig.4h) representing the [001] orientation (\u003cem\u003ec\u003c/em\u003e-axis) dominate and are widely distributed, indicating a pronounced \u003cem\u003ec\u003c/em\u003e-axis texture along the RD.\u0026nbsp;In contrast, the IPF map for the TD direction (Fig.4f) shows no significant orientation preference, which results from its perpendicular alignment to the radial direction. The ND-direction IPF (Fig.4g) exhibits extensive distribution of blue and green regions corresponding to [100] and [010] orientations (\u003cem\u003ea\u003c/em\u003e- and \u003cem\u003eb\u003c/em\u003e-axes), demonstrating predominant \u003cem\u003ea-b\u003c/em\u003e plane alignment along the ND. The pole figure (PF) of the {001} (\u003cem\u003ea-b\u003c/em\u003e plane) of the Y123 phase shows that the poles are concentrated along the RD direction (Fig.4i), further indicating that the normal direction of the {001} planes is parallel to the RD. This suggests that the \u003cem\u003ea\u0026ndash;b\u003c/em\u003e planes of the Y123 grains are preferentially oriented along the longitudinal direction of the superconducting wire, forming a texture. An isolated analysis of Ag\u003csub\u003ex\u003c/sub\u003e grain orientations (Supplementary Fig27a,b) revealed a remarkable alignment with Y123 textures. In contrast, Y\u003csub\u003e2\u003c/sub\u003eBaCuO\u003csub\u003e5\u003c/sub\u003e (Y211), serving solely as a secondary phase, exhibited conventional flux-pinning behavior without distinct grain orientation characteristics\u003csup\u003e55\u003c/sup\u003e (Supplementary Fig.27c,d). The kernel average misorientation (KAM) map (Supplementary Fig.28) indicates that 99.4% of grains exhibit KAM values below 2\u0026deg;, suggesting remarkably low internal strain accumulation during the 3D printing, freeze-drying, and high-temperature co-sintering processes. The average grain size of Y123 was measured to be 1.12 \u0026mu;m (Supplementary Fig.29), significantly smaller than the 1.73 \u0026mu;m observed in SC-YBCO (Supplementary Fig.30a), demonstrating effective grain refinement through process optimization. Under identical sample coordinates, the triaxial IPF maps of the SC-YBCO wire cross-section reveal randomly distributed crystallographic orientations (Supplementary Fig.30b-h). The PF shows disordered distributions of {100}, {010}, and {001} poles (Supplementary Fig.30i). This non-preferential orientation behavior stands in sharp contrast to the strong texturing observed in Ag-core YBCO composite wires.\u003c/p\u003e\n\u003cp\u003eWe performed magnetization measurements with the magnetic field perpendicular to the wires (H∥\u003cem\u003ec\u003c/em\u003e-axis) to evaluate the superconductivity of SC-YBCO, Ag-core YBCO and Ag-coated YBCO wires, including \u003cem\u003eT\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e and \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e. The Ag-core YBCO wire exhibited a \u003cem\u003eT\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e of 90 K under zero-field-cooled (ZFC) conditions (Fig.4j). Both SC-YBCO and Ag-coated YBCO showed comparable \u003cem\u003eT\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e values of 91 K and 90 K respectively (Supplementary Fig.31a,d). Figure 4k, Supplementary Fig.31b,e present the magnetization curves of the three wire types. The Ag-composite YBCO exhibits significantly higher magnetization than SC-YBCO. The width of the perpendicular magnetization hysteresis loops (\u003cem\u003e∆M\u003c/em\u003e) correlates with\u003cem\u003e\u0026nbsp;J\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e, which was analyzed along the wire axis using the extended Bean model\u003csup\u003e31,56\u003c/sup\u003e (Supplementary Information, section 9 and Supplementary Fig.32):\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"352\" height=\"33\"\u003e\u003c/p\u003e\n\u003cp\u003eWhere \u003cimg src=\"data:image/png;base64,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\" width=\"127\" height=\"16\"\u003e with \u003cem\u003eR\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e and \u003cem\u003eR\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e being the inner and outer radii of the YBCO layer, respectively. The linear \u003cem\u003eM\u0026ndash;H\u003c/em\u003e response observed in 3D-printed pure Ag at 10 K (Supplementary Fig.33) confirms that the superconductivity of the composite wire arises exclusively from the YBCO shell. Moreover, we developed a generalized \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e calculation model applicable to both SC-YBCO and Ag-coated YBCO wires (Supplementary Information, section 9 and Supplementary Fig.34). The model-derived \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e values of Ag-core YBCO at various temperatures (Fig.4l) indicate a value of 1.73\u0026times;10\u003csup\u003e4\u0026nbsp;\u003c/sup\u003eA\u0026middot;cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e at 10 K, surpassing that of SC-YBCO (4.45\u0026times;10\u003csup\u003e3\u003c/sup\u003e A\u0026middot;cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e at 10 K; Supplementary Fig.31c), representing a 3.9-fold enhancement (Supplementary Fig.35a). This enhancement is consistent with previous studies, indicating that the addition of Ag into YBCO does not compromise its superconducting properties. On the contrary, it markedly enhances \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e by strengthening flux pinning effects\u003csup\u003e57,58\u003c/sup\u003e. Notably, the \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003eof Ag-core YBCO is comparable to Ag-coated YBCO (1.68\u0026times;10\u003csup\u003e4\u003c/sup\u003e A\u0026middot;cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e at 10 K; Supplementary Fig.31f and Fig.35b), though the latter exhibits faster \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e degradation under increasing magnetic fields (Supplementary Fig.35c). When the applied field is aligned parallel to either the \u003cem\u003ec\u003c/em\u003e-axis or \u003cem\u003ea-b\u003c/em\u003e planes, Ag-core YBCO wires demonstrate pronounced anisotropic behavior, consistent with the characteristics of directionally solidified samples reported in the literature\u003csup\u003e59\u003c/sup\u003e. To ensure the critical current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e) measurement fidelity during cryogenic conditions, the Ag-core YBCO wire surfaces were protected by magnetron-sputtered copper layers (10 \u0026mu;m thick, Supplementary Fig.36a) that simultaneously provided excellent electrical contact and thermal stabilization. The sample was cooled to 26 K in a custom-designed Dewar system. Due to spatial constraints within the Dewar, a ~5 cm-long copper-plated wire segment was selected and fabricated into the test device structure shown in Supplementary Fig.36b. Using a four-probe measurement system, reliable \u003cem\u003eI\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003es were obtained (Fig.4m). Three independent tests yielded \u003cem\u003eI\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e values of 25.45, 21.86, and 23.31 A, corresponding to \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e of 1.27\u0026times;10⁴ ,1.09\u0026times;10⁴, and 1.16\u0026times;10⁴ A\u0026middot;cm⁻\u0026sup2;, respectively. These results confirm the current-carrying capacity of Ag-core YBCO composite wires under low-temperature conditions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMechanical characterization of YBCO superconducting wire\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 5a presents the stress-strain curves of Ag-core YBCO superconducting wires under tensile testing at room temperature (RT) and 77 K. Compared to RT, the superconducting wires exhibit a significantly higher elastic modulus at 77 K. The stress reaches its peak value (25.16 MPa) at 0.25% of strain at 77 K, followed by abrupt fracture, characteristic of typical brittle failure. At temperature of RT, after reaching the maximum stress (22.26 MPa), the curve displays a small stress plateau during the descending phase, indicating that the plastic deformation capability of the Ag core partially alleviates brittle fracture, resulting in fracture strain of 1.25%. Fractographic analysis at RT (Fig.5b) shows a smooth fracture surface in the YBCO layer, dimpled ductile fracture in the Ag core, and a 5~10 \u0026mu;m wide plastic bonding zone at their interface\u003csup\u003e60\u003c/sup\u003e. Three-point bending tests were conducted on Ag-core YBCO wires and 3D-printed YBCO (3DP-YBCO) bulk samples (5 \u0026times; 5 \u0026times; 45 mm\u003csup\u003e3\u003c/sup\u003e) with a span length of 30 mm (Supplementary section 10). The resulting stress-strain curves of both samples at RT and 77 K (Fig.5c) reveal fundamentally distinct mechanical behaviors between Ag-core YBCO wires and 3DP-YBCO bulk materials. The Ag-core YBCO wires exhibit pronounced plastic deformation characteristics under both temperatures. At RT, they demonstrate typical elastoplastic response with a yield strength (\u003cem\u003e\u0026sigma;\u003c/em\u003e\u003csub\u003eb\u003c/sub\u003e) of 19.26 MPa and fracture strain of 4.30%. At 77 K, cryogenic hardening elevates \u003cem\u003e\u0026sigma;\u003c/em\u003e\u003csub\u003eb\u003c/sub\u003e to 33.28 MPa while maintaining 1.0% plastic deformation capability. In stark contrast, the 3DP-YBCO bulk displays characteristic brittle fracture behavior achieving fracture strength of 1.96 MPa (at 2.68% of strain) at RT and the strength of 8.86 MPa at 77 K, but with strain capacity drastically reduced to 0.027%. This behavioral dichotomy demonstrates that the Ag-core architecture enhances fracture energy of YBCO from 52.2 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e (bulk) to 1361.8 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e (wire) at RT which is a 26-fold improvement. The\u0026nbsp;enhancement becomes even more remarkable at 77 K (209-fold), where the bulk material shows only 2.4 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e compared to the wire\u0026apos;s 502 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e (Fig.5d). Consistent with literature reports, the incorporation of Ag markedly improves the mechanical properties of the YBCO system, particularly in terms of fracture toughness and bending strength\u003csup\u003e53,61\u003c/sup\u003e. The detailed mechanical parameters obtained from tensile and three-point bending tests are summarized in Supplementary Table 7. The three-point bending fractography further reveals dimple structures in the Ag core at RT (Fig.5e). Supplementary Video 2 demonstrates the dynamic response of the superconducting wire during loading through in situ SEM three-point bending tests. SEM characterization (Fig.5f,g) indicates that the toughening effect of the Ag-core structure alters the crack propagation mode in YBCO from intergranular to transgranular fracture. Cracks propagate through YBCO grains, creating straight and sharp fracture surfaces\u003csup\u003e62\u003c/sup\u003e (Supplementary Fig.37a-c). In contrast, cracks in 3DP-YBCO bulk preferentially propagate along weakly bonded grain boundaries, forming rough intergranular fracture surfaces that reflect the tortuous crack path around grains (Supplementary Fig.37d-f). Micro-Vickers hardness testing of Ag-core YBCO superconducting wires under varying indentation loads (Fig.5h, Supplementary Fig.38 and Supplementary Table 8) reveals a distinct hardness gradient: YBCO exhibits the highest hardness, followed by the Ag/YBCO interface, with the pure Ag core showing the lowest values. Nanoindentation tests conducted at different penetration depths (400, 800, and 1200 nm; Supplementary Fig.39) demonstrate an anomalous mechanical response which displays higher hardness in Ag core and elastic modulus than both YBCO and the interface region at all tested depths.\u003c/p\u003e"},{"header":"Discussion and outlook","content":"\u003cp\u003eIn early studies on YBCO superconducting round wires, the four-probe \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e measurement employed a relatively short voltage lead spacing (~4 mm)\u003csup\u003e22\u003c/sup\u003e. This experimental configuration may lead to an overestimation of \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e due to insufficient voltage drop measurement region.\u0026nbsp;Notably, neither Ponnusamy et al.\u003csup\u003e23\u003c/sup\u003e nor Grader et al.\u003csup\u003e24\u003c/sup\u003e explicitly reported the test temperature for \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e in their studies. The absence of this critical parameter hinders a\u0026nbsp;meaningful cross-comparison with our research findings.\u0026nbsp;Although Ponnusamy et al.\u003csup\u003e23\u003c/sup\u003e reported a 140 cm-long YBCO superconducting wire, their graphical data reveal multiple discontinuities along the sample. The researchers presumably employed methods such as soldering or foil wrapping to reconnect these breaks; however, they provide no detailed description of these procedures.\u0026nbsp;Most remarkably, they achieved a YBCO wire with a remarkably small diameter of just 1.6 mm yet exhibiting an exceptional bending fracture strength of 170 MPa\u003csup\u003e23\u003c/sup\u003e. In contrast, the TSMTG sample (3 \u0026times; 4 \u0026times; 18 mm\u003csup\u003e3\u003c/sup\u003e) exhibited a bending fracture strength of merely 104 MPa\u003csup\u003e63\u003c/sup\u003e, potentially attributable to the higher density of their wire fabrication.\u003c/p\u003e\n\u003cp\u003eIn this paper, we investigated a controllable fabrication strategy for YBCO superconducting round wires, enabling continuous and uninterrupted 3D printing at the meter-length scales while maintaining high superconductivity after sintering. The Ag-core/YBCO-shell long-wire configuration exhibits significant structural advantages for power transmission applications. This coaxial composite design enables spatial separation of mechanical and electrical functionalities: the Ag core, owing to its excellent ductility and electrical conductivity, serves as both structural support and current shunt following a local quench, whereas the outer YBCO shell, with its superior superconducting properties, functions as the primary current-carrying channel.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn addition, we have systematically revealed the interfacial effects in the Ag-YBCO system across multiple scales. The freeze-drying process creates a radial porous structure within the YBCO shell, which provides effective diffusion pathways for the outward migration of Ag particles during high-temperature heat treatment. This distinctive diffusion behavior significantly modulates the microstructure of YBCO grains through interfacial composite effects, ultimately achieving synergistic enhancement of the material\u0026apos;s overall performance. The introduction of Ag cores facilitates the formation of Y123 superconducting grains, leading to synchronized enhancement in both \u003cem\u003eJ\u003csub\u003ec\u003c/sub\u003e\u003c/em\u003e and mechanical properties primarily through three mechanisms:\u003c/p\u003e\n\u003cp\u003e(i) It promotes a bridging effect among superconducting grains, leading to the formation of interconnected network structures. This enables observable current transport behavior at low temperatures through direct transport measurements, rather than relying solely on \u003cem\u003eJ\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e values inferred from magnetic measurements.\u003c/p\u003e\n\u003cp\u003e(ii) It forms a solid solution Ag\u003csub\u003ex\u003c/sub\u003e through lattice substitution, which regulates the grain orientation of Y123. Ag partially substitutes into the Y123 crystal lattice, forming an Agₓ phase with a [001] orientation. Due to the coherent interfacial relationship between the Agₓ phase and the Y123 lattice, this orientation feature can induce subsequent Y123 grain growth along the [001] direction, thereby facilitating the texturing of the superconducting round wire. Unlike conventional TSMTG, in this study, the texturing is intrinsically driven by the solid solution, eliminating the need for seed crystals.\u003c/p\u003e\n\u003cp\u003e(iii) It affects the mechanical behavior of the grains between Ag and Y123. We found that the significant improvement in tensile and bending performance originates from a shift in the crack propagation mechanism\u0026mdash;from intergranular to transgranular fracture. The ductile fracture characteristics of the Ag core are transmitted to the YBCO shell, resulting in a visible plastic plateau in the stress\u0026ndash;strain curve.\u003c/p\u003e\n\u003cp\u003eIn summary, we designed and developed a bimaterial 3D printing platform featuring both low pressure difference and low flow rate difference. Through systematic investigation of the rheological properties of the dual-ink system, we achieved the high-efficiency 3D printing of Ag-core/YBCO-shell round wires with diameters below 1 mm and lengths exceeding 1 meter.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eFour-probe transport measurements on long sample achieved 1.27 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e A\u0026middot;cm\u003csup\u003e-2\u003c/sup\u003e at 26 K, whereas 3D-printed pure YBCO wires failed to achieve current transport due to particle dispersion. Three-point bending tests showed a fracture energy reached 1361.8 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e at room temperature, which is 26 times higher than that of the bulk sample (52.2 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e). We confirmed the existence of a substitute doping mechanism of Ag in the YBCO system and elucidated the synergistic optimization mechanism of Ag doping on both the superconductivities and mechanical properties of YBCO. Our findings provide a direct experimental explanation for the long-standing question of \u0026quot;Ag doping enhancing YBCO performance while the underlying mechanism remained unclear\u0026quot; in the research community. Furthermore, this core/shell structure is inherently compatible with multifilamentary cable designs, facilitating the construction of high-current-capacity superconducting cable systems.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eInk Preparation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYBCO precursor powder synthesis: Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (99.99%, Macklin), CuO (99.5%, Macklin), and BaCO\u003csub\u003e3\u003c/sub\u003e (99.95%, Macklin) were mixed in a stoichiometric molar ratio (Y: Ba: Cu = 1:2:3) with anhydrous ethanol and ball-milled using a planetary mill (MSK-SFM-1). The mixture was then dried at 90\u0026deg;C for 12 h in an oven to obtain YBCO precursor powder.\u0026nbsp;Aqueous binder solution formulation: sodium carboxymethyl cellulose (CMC, [C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003eOCH\u003csub\u003e2\u003c/sub\u003eCOONa]\u003csub\u003en\u003c/sub\u003e; viscosity: 600-1000 mPa\u0026middot;s; Macklin) was dissolved in deionized water at 6.5 wt.% under mechanical stirring for 2 h to serve as the binder. Oil-based binder solution formulation: ethyl cellulose (EC, (C\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e22\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e)\u003csub\u003en\u003c/sub\u003e; viscosity: 300 mPa\u0026middot;s; Macklin) was dissolved in\u0026nbsp;diethylene glycol monobutyl ether (C\u003csub\u003e8\u003c/sub\u003eH\u003csub\u003e18\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, 99%, Macklin) at 5 wt.%, under mechanical stirring for 2 h at 60\u0026deg;C in a water bath.\u0026nbsp;3D Printing ink preparation for Ag-core YBCO wires: The aqueous YBCO ink was prepared by mixing 50 g YBCO precursor powder with 15 mL of an aqueous binder solution, followed by the addition of 5 g Epoxidized soybean oil (ESO, C\u003csub\u003e57\u003c/sub\u003eH\u003csub\u003e98\u003c/sub\u003eO\u003csub\u003e18\u003c/sub\u003e, Aladdin) and homogenization through roller milling (3 cycles). The commercial Ag/Pd paste (Sryed Paste) was used directly as the oil-based Ag ink.\u0026nbsp;3D printing ink preparation for Ag-coated YBCO wires:\u0026nbsp;The aqueous Ag ink was formulated blending 50 g of Ag nanoparticles (200 nm, 99.99%, Macklin) with 30 mL of an aqueous binder solution and 6 g of ESO, followed by roller milling for 3 cycles. The oil-based YBCO ink was prepared by combining 50 g of YBCO precursor powder with 20 mL oil-based binder solution and 4 g of glycerol (C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, 99%, Macklin), then homogenized via roller milling (3 cycles).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFabrication of YBCO Superconducting Wires via Bimaterial DIW 3D Printing\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe oil-based ink was loaded into a modified DIW 3D printer (Bio-Architect PRO, Regenovo, China) through the inner feed port of the nozzle, with pneumatic extrusion controlled at a pressure of 0.15 MPa. Simultaneously, the aqueous ink was delivered via an external syringe pump connected to the outer feed port\u0026nbsp;of the optimized printing nozzle, maintaining a flow rate of 1.0 mL/min. The robotic arm was programmed to move along the \u003cem\u003eX/Y\u003c/em\u003e axes at a speed of 2.0 mm/s during deposition (Supplementary Video 1). Printed samples were immediately cryo-cast at -80\u0026deg;C for 24 h, followed by freeze-drying to obtain green wires. These wire precursors were subsequently annealed in a tube furnace under an oxygen atmosphere using the thermal profile shown in Supplementary Fig.6 to finalize the YBCO superconducting wires.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterial and structure characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eX-ray diffraction (XRD) analysis was performed using an X\u0026apos; Pert PRO MPD diffractometer (PANalytical, Netherlands) with Cu \u003cem\u003eK\u0026alpha;\u003c/em\u003e radiation over a 2\u003cem\u003e\u0026theta;\u003c/em\u003e range of 5\u0026deg;\u0026ndash;90\u0026deg;. Microstructural characterization was conducted using field-emission scanning electron microscopy (FE-SEM, Apreo S, Thermo Fisher Scientific, USA) equipped with energy-dispersive X-ray spectroscopy (EDS, Octane Pro, AMETEK, USA) for elemental mapping at a working distance of 10 mm and accelerating voltage of 15 kV.\u0026nbsp;\u0026nbsp;Transmission electron microscopy (TEM, Talos F200s, Thermo Fisher Scientific, USA) coupled with a Super-X EDS system (Bruker, Germany) was employed for nanoscale compositional analysis. \u0026nbsp;Crystallographic orientation analysis was performed via electron backscatter diffraction (EBSD, Symmetry S2, Oxford Instruments, UK) operating at 20 kV with a step size of 50 nm and acquisition rate exceeding 300 points per second (pps). Thermogravimetric analysis (TGA) was carried out using a simultaneous TGA/differential scanning calorimetry (DSC) analyzer (TGA/SDTA 851e, Mettler-Toledo, Switzerland) from 25\u0026deg;C to 1000\u0026deg;C at a heating rate of 2\u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e under nitrogen atmosphere.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMeasurements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eRheological properties were measured using a rotational rheometer (MCR302, Anton Paar, UK) at 25\u0026deg;C, performing both steady-state shear (0.01-100 s\u003csup\u003e-1\u003c/sup\u003e) and dynamic oscillatory tests (1 Hz, 0.01-3000 Pa). Superconducting properties were characterized by SQUID magnetometry (MPMSR2, Quantum Design, USA), including zero-field-cooled (ZFC, 50 Oe) magnetization curves and temperature-dependent hysteresis loops (10, 35, 55, and 77 K, \u0026plusmn;70 kOe). Electrical transport measurements were conducted via the four-point probe method (SMS600C-H-4Q current source, Cryogenic, UK) at 26 K to determine critical current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e). Copper coatings were deposited by magnetron sputtering (Mantis Deposition, UK) using a 99.999% pure copper target (Kurt J. Lesker, USA) under 5\u0026times;10\u003csup\u003e-6\u003c/sup\u003e Torr base pressure, with 100 W RF power and 3 mTorr argon working pressure, resulting in 10 \u0026mu;m-thick coatings. Mechanical characterization included: in situ SEM three-point bending tests (Quanta 650 FEG SEM, FEI, USA with Deben Microtest 5kN module, UK), tensile tests (UTM4104, China), and conventional three-point bending (20 mm span, 0.1 mm/min loading rate). Hardness was evaluated using micro-Vickers (FM-700, Future-Tech, Japan) and nanoindentation (TI-950, Hysitron, USA with Berkovich diamond tip). All mechanical tests were performed at both room temperature and 77 K (custom liquid nitrogen Dewar).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank Huadong Yong, Zhiwei Zhang and Yajun Zhang,\u0026nbsp;Lanzhou University\u0026nbsp;for enlightening discussions. We also appreciate Yihao Li, Chuanguang Liu, Jihua Deng, and Yunfan Shi for their assistance in the four-probe measurements at low temperatures.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNational Key Research and Development Program of China grant 2024YFB4607300\u003c/p\u003e\n\u003cp\u003eNational Natural Science Funds for Distinguished Young Scholar grant 12325205\u003c/p\u003e\n\u003cp\u003eDistinguished Talent Research Funding of Lanzhou grant 127000-563225112\u003c/p\u003e\n\u003cp\u003eScience and Technology Leading Talent Project of Gansu Province grant 24RCKB008\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eF. Y. Z and B. Q. Z. contributed equally to this work. X. Y. Z., B. Q. Z. developed the concept. X. Y. Z., B. Q. Z., F. Y. Z., X. Y. S. and Y. T. Z. designed the overall experiments. F. Y. Z and X. Y. S. conducted the computational predictions and simulation analysis. F. Y. Z designed the 3D printing experiment and write original draft. F. Y. Z. and, Y. T. Z conducted the material synthesis for 3D printing and characterization. X. Y. Z., Y. H. Z. and B. Q. Z for Funding, supervision and project administration. X. Y. Z., B. Q. Z., F. Y. Z collectively wrote and revised the paper. All authors discussed the results and commented on the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData and materials availability:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll data are available in the main text or the supplementary materials.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBanno, N. 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However, long-length round wires, with the greatest potential for power transmission and large-scale magnets, still face challenges: due to the material’s intrinsic brittleness, difficulties in ensuring structural integrity and uniformity during sintering, and ineffective control over crystallographic texture within the round-wire geometry. Herein, we present a direct-ink-writing bimaterial 3D printing strategy to continuously fabricate submillimeter-diameter Ag/YBCO composite wires. Silver paste and ceramic slurry are used as precursors to form core-shell filaments. During the sintering process under an oxygen environment, Ag+ incorporates into YBCO lattice, which forms coherent interfaces with the superconducting phase and promotes [001] grain growth in round-wire. This texture forms intrinsically through solid solution, distinct from conventional seed-mediated or buffer-layer-assisted methods. Electrical transport measurements achieved a transport critical current density of 1.27×104 A·cm-2 @26 K, along with a high bending fracture energy of 1361.8 MJ·m-3. This work paves the way for scalable fabrication of long-length and high-performance superconducting round wires for magnets and compact power transmission cables.","manuscriptTitle":"Ag/YBCO superconducting round wires fabricated by bimaterial 3D printing","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-21 03:43:06","doi":"10.21203/rs.3.rs-7301425/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2b4417bf-d144-440c-aa99-a8d7e7a0c76d","owner":[],"postedDate":"August 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":53476253,"name":"Physical sciences/Physics/Condensed-matter physics/Superconducting properties and materials"},{"id":53476254,"name":"Physical sciences/Materials science/Structural materials/Composites"}],"tags":[],"updatedAt":"2025-09-22T04:25:40+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-21 03:43:06","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7301425","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7301425","identity":"rs-7301425","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}