Effect of Simultaneous Addition of Three Sintering Aids: magnesium, lanthanum, and zirconium oxide on the Mechanical and optical properties of Alumina Ceramics fabricated by SPS Method

Effect of Simultaneous Addition of Three Sintering Aids: magnesium, lanthanum, and zirconium oxide on the Mechanical and optical properties of Alumina Ceramics fabricated by SPS Method | 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 Effect of Simultaneous Addition of Three Sintering Aids: magnesium, lanthanum, and zirconium oxide on the Mechanical and optical properties of Alumina Ceramics fabricated by SPS Method Amirhossein Karimi shargh, Mazaher Ramazani, Hossein Jamali, Fatemeh Davar, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6268009/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Jul, 2025 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract This study investigates the synergistic effects of a novel triplex sintering aid system—magnesium oxide (MgO), lanthanum oxide (La₂O₃), and zirconium oxide (ZrO₂)—on the mechanical and optical properties of transparent alumina ceramics fabricated using spark plasma sintering (SPS). The specimens were sintered at 1350°C for 10 minutes under 70 MPa pressure. The sample with the highest zirconia content (sample Z: 100L100M300Z) achieved a bulk density of 3.94 g/cm³, corresponding to 99.9% of the theoretical density of alumina. This sample exhibited an infrared transmission of 71.4% at 5 µm and a visible transmittance of 32% at 750 nm, surpassing values reported for single or dual sintering aid systems. Mechanical testing revealed a microhardness of 19.34 ± 0.1 GPa and a fracture toughness of 5.24 MPa.m⁰·⁵ for sample Z. Additionally, this sample demonstrated the highest flexural strength of 356.83 MPa, attributed to its finer grain size, reduced porosity, and the synergistic effects of the triplex sintering aids. The results demonstrate a promising pathway for producing high-performance transparent alumina ceramics with tailored properties for demanding optical and mechanical applications. Physical sciences/Chemistry Physical sciences/Engineering Physical sciences/Materials science Physical sciences/Materials science/Materials for optics Alumina triplex sintering aid transparency ceramics SPS Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction Alumina ceramics are highly valued for their exceptional mechanical properties, electrical insulation, and thermal stability, making them suitable for a wide range of industrial applications. Transparent alumina ceramics, in particular, are critical for use in armor, sensors, and advanced optical systems due to their impressive strength, thermal stability, and optical transparency. Alpha-alumina is a prominent material for infrared windows, offering 50–70% infrared transmission in the 3–5 µm wavelength range and excellent mechanical properties. However, its low impact resistance and fracture toughness remain significant limitations. These limitations can be addressed by optimizing sintering conditions to reduce temperature and time while maintaining a fine grain structure [ 1 – 5 ]. The performance of alumina ceramics can be significantly enhanced through the addition of appropriate sintering aids, particularly dual systems such as MgO-Y₂O₃, MgO-La₂O₃, or MgO-ZrO₂. These systems have been shown to improve density and mechanical properties in transparent alumina [ 3 – 5 ]. In this study, we investigate the combined effects of three sintering aids—magnesium oxide (MgO), lanthanum oxide (La₂O₃), and zirconium oxide (ZrO₂) —on the properties of alumina ceramics produced using the SPS method. Achieving high visible and infrared transparency in ceramics requires minimizing light scattering and ensuring that grain sizes are significantly smaller than the incident wavelength. Thus, achieving full density during sintering and preventing excessive grain growth are essential. The choice of sintering method is critical, and the SPS technique is particularly advantageous for producing materials with high density, short sintering times, and fine grain structures [ 6 , 7 ]. In addition to sintering strategies, the use of sintering aids can inhibit grain growth, enhance density, and improve mechanical properties. However, the optimal amount of each additive must be carefully selected. Insufficient amounts may fail to achieve the desired optical properties, whereas excessive amounts can lead to porosity or secondary phase formation, thereby reducing transparency. For instance, Ge et al. demonstrated that 100 ppm La₂O₃ improves compactness and bulk density in alumina ceramics, reducing apparent porosity and enhancing mechanical properties [ 8 ]. Similarly, La³⁺ ions have been shown to curb grain growth, improving both infrared and visible transmission. However, increasing La₂O₃ concentration beyond 100 ppm does not further inhibit grain growth [ 8 , 9 ]. Studies have also shown that triple additive systems, such as MgO-La₂O₃-Y₂O₃, enhance real in-line transmittance (RIT) compared to dual or additive-free systems. This improvement is attributed to the synergistic effects of the triple combination, with MgO playing a pivotal role by creating oxygen vacancies in the alumina structure, which facilitates the incorporation of Y and La atoms [ 10 ]. Apak et al. [ 11 ] investigated the effects of Y₂O₃ and MgO on the mechanical properties of alumina, producing transparent ceramics via SPS at 1300°C and 1340°C under 80 MPa pressure for 5 minutes. Their samples achieved densities ranging from 97.1–99.9%, and higher MgO concentrations (up to 300 ppm) resulted in increased density. Another study examined the influence of MgO on visible transmission at various sintering temperatures (1300, 1500, and 1700°C), finding that 300 ppm MgO at 1300°C yielded the highest transparency [ 12 ]. Additionally, zirconia additives have been shown to refine alumina grain structure, though concentrations above 300 ppm do not further enhance light transmission [ 9 , 13 ]. While extensive research has explored the effects of single and dual sintering aids (e.g., MgO, La₂O₃, and ZrO₂) on the optical and mechanical properties of transparent alumina, no studies have comprehensively evaluated the simultaneous addition of MgO, La₂O₃, and ZrO₂ on the microstructure, light transmission, and the full suite of mechanical properties (e.g., hardness, fracture toughness, and flexural strength) of alumina. This study aims to address this gap by investigating the synergistic effects of a triple sintering aid system on the properties of SPS-processed alumina ceramics. 2. Experimental 2.1. Synthesis of Precursors and Sintered Samples In this study, α-alumina powder with a particle size of 200 nm and high purity (99.9%) was purchased from US Research Nanomaterials Inc. The chemical precipitation process for the sintering aids involved using magnesium nitrate (Mg(NO₃)₂), lanthanum nitrate (La(NO₃)₃), and zirconium chloride (ZrOCl₂) salts, all sourced from Merck, Germany. Initially, a slurry was prepared by dispersing 2.2 g of nanosized alumina in 50 mL of deionized water. Subsequently, magnesium nitrate, lanthanum nitrate, and zirconium oxychloride were added according to the compositions specified in Table 1 . By adding ammonia and adjusting the pH to 9.5, hydroxide ions (Mg²⁺, La³⁺, Zr⁴⁺) were precipitated onto the suspended alumina particles. The resulting slurry was dried in an oven at 60°C for 8 hours, followed by calcination at 800°C to convert the hydroxides (Mg(OH)₂, La(OH)₃, and Zr(OH)₄) into their corresponding metal oxides (MgO, La₂O₃, and ZrO₂. Table 1 Composition, sample codes, and Archimedes density of samples prepared with different amounts of sintering aids. ZrOCl 2 .8H 2 O (g) Mg(NO 3 ) 2 .6H 2 O (g) La(NO 3 ) 3 .6H 2 O (g) Relative density (%) ppm of sintering aid Sample code 0.0002 0.00127 0.0005 98.7 100MgO-100La 2 O 3 -50ZrO 2 G: 100M-100L-50Z .0002 0.0025 0.0005 97.1 200 MgO − 100 La 2 O 3 -50 ZrO 2 H: 200M -100 L-50 Z .00005 0.00127 0.0005 98.7 100 MgO − 100 La 2 O 3 -100 ZrO 2 X: 100M -100 L-100Z .0005 0.0025 0.0005 99.1 200 MgO − 100 La 2 O 3 -100 ZrO 2 Y: 200M -100L-100Z 0.00156 0.00156 0.0005 99.9 100 MgO − 100 La 2 O 3 -300 ZrO 2 Z: 100 M -100 L-300 Z - 0.00127 - 96.1 100 MgO 100M - 0.00127 0.0005 97.9 100 MgO − 100 La 2 O 3 100M100L 0.00156 0.00127 0.0005 98.1 100 MgO − 300 ZrO 2 100M300Z Sample consolidation was performed using a spark plasma sintering (SPS) machine (manufactured by MUT University, Iran) at a temperature of 1350°C, with a heating rate of 50°C/min, under a pressure of 70 MPa for 10 minutes. Graphite molds with a diameter of 2 cm were used for the sintering process. 2.2. Characterization Techniques X-ray diffractometry (XRD): Performed using an X’Pert Pro MPD device (Panalytical, Netherlands) with a copper X-ray tube (wavelength: 1.542 Å), operating at 40 kV and 25 mA. The step size was set to 0.03 degrees. Field emission scanning electron microscopy (FESEM): Structural investigations were performed using an FEI model (USA). Density measurements: Evaluated using Archimedes’ method. Visible-ultraviolet (UV-Vis) transmission tests: Conducted over a wavelength range of 200–800 nm using a Ray Leigh UV-1600 device. Infrared (IR) transmission tests: Investigated using Infralum FT-08 LUMEX infrared spectroscopy. Three-point bending tests: Performed using a Hounsfield H25KS (England) equipped with a 500 N load cell, moving at a speed of 0.1 mm/min. Microhardness testing: Conducted using a 101/642-MiTi model (Mitutoyo, Japan) by applying a 1 kg load for 10 seconds. 3. Results and Discussion 3.1. Structural and Phase Analysis The X-ray diffraction (XRD) pattern of the initial alumina powder is presented in Fig. 1 . The diffraction peaks correspond to α-alumina (JCPDS card no. 01-073-1512), with lattice parameters of a = 0.47544 nm and c = 1.297 nm, confirming a rhombohedral crystal structure. Using the Williamson-Hall method, the crystallite size of the alumina powder was calculated to be 43.4 nm. The XRD patterns of the bulk samples with different sintering aid compositions, after SPS treatment at 1350°C are shown in Fig. 2 . Due to the detection limit of XRD (phases below 5 wt.% are not detectable), all samples exhibited diffraction patterns consistent with the α-alumina phase, with no evidence of additional or decomposed phases. 3.2. Microstructural Analysis Scanning electron microscopy (SEM) images of the α-alumina powder with the three sintering aids (MgO, La₂O₃, and ZrO₂) are presented in Fig. 3 . The images reveal alumina nanoparticles with sizes ranging from 200 to 250 nm, alongside smaller particles (< 100 nm) attributed to the precipitated sintering aids after calcination at 800°C. Energy-dispersive X-ray spectroscopy (EDS) analysis of the samples with compositions 100M100L300Z and 100M100L50Z is shown in Fig. 4 . The EDS results indicate that the weight percentages of lanthanum, magnesium, and zirconium exceeded the theoretical values due to fluorescence errors inherent in the EDS analysis. 3.3. Density and Microstructure The bulk density of all samples, as evaluated by Archimedes’ method, is summarized in Table 1 . The results show that the 100M-100L-300Z (Z) sample, with the highest zirconia content (300 ppm), achieved the highest bulk density of 3.94 g/cm³, corresponding to 99.9% of the theoretical density of α-alumina. This improvement is attributed to the role of zirconia in reducing surface tension and grain boundary energy, thereby enhancing the sintering process and promoting denser microstructures [ 8 , 9 , 14 – 18 ]. The high bulk density (3.94 g/cm³) achieved in the 100M100L300Z sample is a direct result of the combined effects of the triple sintering aids. The addition of ZrO₂ reduces surface tension and grain boundary energy, promoting densification during the sintering process [ 9 , 13 ]. Meanwhile, MgO and La₂O₃ stabilize the microstructure and prevent the formation of pores, further enhancing the density of the material [ 8 – 11 ]. The ability to achieve near-theoretical density in such a short sintering time is a testament to the effectiveness of the triplex sintering aid system, as it allows for the production of high-performance transparent alumina ceramics with minimal defects. Field emission scanning electron microscopy (FESEM) images of the fracture surfaces of the prepared samples are shown in Fig. 5 . The 100M-100L-300Z (Z) sample exhibited the smallest grain size and no observable porosity, confirming its superior densification. The microstructure of the 100M100L300Z sample, characterized by its fine grain size and lack of observable porosity, is a direct result of the synergistic effects of the triple sintering aids. The addition of ZrO₂ inhibits grain growth through its phase transformation mechanism, while MgO and La₂O₃ stabilize the grain boundaries and prevent the formation of secondary phases. This combination of effects results in a dense, uniform microstructure that is essential for achieving both high optical transparency and mechanical strength. The ability to control grain size and porosity through the use of multiple sintering aids is a key advantage of the triplex system, as it allows for the development of materials with tailored properties for specific applications. 3.4. Elemental Distribution X-ray mapping of the elemental distribution in the Z sample is presented in Fig. 6 . The analysis confirms the uniform distribution of Zr, La, and Mg throughout the alumina grains, indicating the effective incorporation of the sintering aids. The uniform distribution of Zr, La, and Mg is crucial for achieving consistent and predictable material properties. The absence of clustering or segregation suggests that the chemical precipitation method effectively dispersed the sintering aids throughout the alumina grains. This uniform dispersion likely contributes to the enhanced densification and grain growth control observed in the subsequent analyses. 3.5. UV-Vis and IR spectra and microstructures The transmission curves for the prepared samples in the visible and infrared ranges are shown in Fig. 7 . The 100M-100L-300Z (Z) sample exhibited the highest visible transmittance of 32% at 750 nm and the highest infrared transmittance of 71.4% at 5 µm. Figure 8 shows photographic images of the sintered samples, demonstrating the visible transparency of the Z and Y samples, as evidenced by the clear visibility of the text "Al₂O₃" placed behind the samples. A comparison of the optical results of this study with other reported works is provided in Table 2 . The infrared transmittance achieved in this work is higher than that of alumina prepared with single sintering aids (e.g., MgO or La₂O₃) or triple sintering aids (e.g., MgO, ZrO₂, and Y₂O₃) [ 12 , 15 , 16 ]. Table 2 Comparison of the optical transmittance of this study with other reported works. Visible transmission (at λ = 750 nm) IR transmission (at λ = 5 µm) T/P Sintering aid content Ref. 35 67 1500°C/ 50 MPa 450 MgO − 450 Y 2 O 3 -450ZrO 2 [ 15 ] - 42 1500°C /80MPa 500 ppm MgO [ 12 ] 20 65 1500°C /70MPa 100 ppm MgO-100 ppm La 2 O 3 [ 16 ] 32 71.4 1350°C /70MPa 100 MgO − 100 La 2 O 3 -300 ZrO 2 Current work Figure S1 (Supporting Information File 1) shows the visible light transmission spectra of the samples with different sintering aid compositions. The sample without sintering aids exhibited no transmission in the visible region. In contrast, samples containing 100 ppm magnesia (100M), 100 ppm magnesia + 100 ppm lanthanum oxide (100M100L), and 100 ppm magnesia + 300 ppm zirconium oxide (100M300Z) showed transmission values of 7%, 14%, and 23%, respectively, at a wavelength of 700 nm. Notably, the sample containing all three sintering aids—100 ppm magnesia, 100 ppm lanthanum oxide, and 300 ppm zirconium oxide (100M100L300Z)—achieved a transmission value of 29% at 700 nm. These results highlight the critical role of the triple sintering aid system in enhancing the optical transparency of alumina ceramics. Figure S2 (Supporting Information File 1) presents cross-sectional field emission scanning electron microscopy (FESEM) images of alumina disks with varying sintering aid compositions. Key observations include: Without sintering aids: The alumina grain size grew to 10 µm, with significant intergranular porosity (indicated by arrows). With 100 ppm magnesia (100M): A mixture of coarse grains (10 µm) and finer grains (50 nm) was observed. With 100 ppm magnesia + 100 ppm lanthanum oxide (100M100L): The grain size decreased to 4–5 µm. With 100 ppm magnesia + 300 ppm zirconium oxide (100M300Z): The grain size further decreased to 3 µm. The number of pores (indicated by arrows) decreased significantly from Figure S2a to S2d, demonstrating the effectiveness of sintering aids in reducing porosity and refining grain structure. 3.6.Mechanical Properties: Microhardness, Fracture Toughness and Flexural Strength The microhardness of the samples was calculated using Eq. 1: (1) \(\:H=0.1891\times\:\frac{P}{2\left({a}^{2}\right)}\) where: H = hardness (GPa), P = applied load (N), a = radius of the indentation (mm). The results, presented in Table 3 , show that the 100M100L300Z (Z) sample exhibited the highest microhardness. For fracture toughness, Eq. 2 was used: Table 3 Hardness and micro-hardness values of the sintered samples. Hardness (GPa) Microhardness (GPa) Sample code 018.56 ± 0.3 19.36 ± 0.2 G: 100M-100L-50Z 18.01 ± 0.5 18.18 ± 0.5 H: 200M -100L-50 Z 16.97 ± 0.2 16.6 ± 0.2 X:100M-100L-100Z 17.51 ± 0.1 17.16 ± 0.1 Y: 200M -100L-100Z 19.34 ± 0.2 19.14 ± 0.1 Z: 100 M -100 L-300 Z (2) \(\:{K}_{IC}=K{\left(\frac{E}{H}\right)}^{\frac{1}{2}}\left(\frac{P}{{c}^{\frac{3}{2}}}\right)\) where: KIC​ = fracture toughness (MPa·m⁰·⁵), K = dimensionless constant (0.0264) [ 18 ], E = elastic modulus (GPa), P = applied load (N), c = crack length (mm). The results, summarized in Table 4 , demonstrate that the 100M100L300Z (Z) sample achieved the highest fracture toughness. The significant improvement in fracture toughness observed in the 100M100L300Z sample can be attributed to the combined effects of the triple sintering aids. ZrO₂, in particular, plays a key role in enhancing fracture toughness through its phase transformation mechanism, which induces compressive stresses that hinder crack propagation. Additionally, the presence of MgO and La₂O₃ at the grain boundaries stabilizes the microstructure and reduces the likelihood of intergranular fracture. This multi-mechanism approach to improving fracture toughness is a key advantage of the triplex sintering aid system, as it allows for the development of transparent alumina ceramics with both high optical transparency and excellent mechanical performance. Table 4 Fracture toughness values of the sintered samples. K IC (MPa.m 0.5 ) C (µm) Sample code 1.48 192.25 G: 100M-100L-50Z 3.29 114.5 X:100M-100L-100Z 3.81 102.5 Y: 200M -100L-100Z 5.24 84 Z: 100 M -100 L-300 Z 3.6.1.Flexural Strength The three-point bending strength of the samples was calculated using Eq. 3: (3) \(\:\sigma\:=\frac{8PL}{\pi\:{D}^{3}}\) where: σ = flexural strength (MPa), P = breaking force (N), L = distance between supports (mm), D = sample diameter (mm). The results, presented in Table 5 and Fig. 9 , show that the 100M100L300Z (Z) sample exhibited the highest flexural strength. This improvement is attributed to the reduction in grain size, lower porosity, and the synergistic effects of the triple sintering aids. Table 5 Flexural strength and grain size values of the sintered samples.Table 6 : Comparison of the properties of this work with other reported studies. Flexural strength (MPa) Grain size (µm) Sample code 269 5 G: 100M-100L-50Z 195 2.5 H: 200M -100L-50 Z 220 2 X:100M-100L-100Z 188 2 Y: 200M -100L-100Z 356 2 Z: 100 M -100 L-300 Z The mechanical properties of the 100M100L300Z sample, including its high hardness (19.34 GPa) and flexural strength (356.83 MPa), are a direct result of the synergistic effects of the triple sintering aids. The fine grain size achieved through the addition of ZrO₂, combined with the grain boundary strengthening effects of MgO and La₂O₃, results in a material with superior resistance to deformation and fracture. The reduction in porosity and the uniform distribution of the sintering aids further contribute to the enhanced mechanical performance, making this material suitable for applications requiring both high strength and optical clarity. 3.7.Role of Sintering Aids in Transparency and Density The high relative density achieved in the 100M100L300Z (Z) sample corresponds to a reduction in porosity, which is crucial for improving transparency. High porosity levels lead to light scattering due to the significant difference in refractive indices between air (n ≈ 1) and alumina (n ≈ 1.76). This scattering results in the darkening of the ceramic. The addition of zirconia (ZrO₂) plays a key role in grain refinement. As shown in Table 1 and the SEM images, increasing the zirconium salt content reduces grain size of alumina. This effect is attributed to the tetragonal-to-monoclinic phase transformation of zirconia, which induces a 3–5% volume expansion and inhibits grain growth at alumina grain boundaries [ 9 , 18 ]. Furthermore, magnesia (MgO) promotes the formation of a stable MgAl₂O₄ spinel phase at grain boundaries, which also prevents alumina grain growth [ 1 – 5 , 21 – 24 ]. The inclusion of lanthanum oxide (La₂O₃) stabilizes the spinel network, further enhancing the microstructure. The synergistic effect of the triple sintering aid system significantly improves the transparency and mechanical properties of alumina. The observed improvements in transparency and mechanical properties can be attributed to several factors. The combination of MgO, La₂O₃, and ZrO₂ creates a multi-faceted approach to controlling grain boundary mobility and defect formation. MgO promotes the formation of MgAl₂O₄ spinel, which not only inhibits grain growth but also scavenges impurities. La₂O₃ stabilizes the spinel structure and reduces oxygen vacancies, while ZrO₂'s phase transformation induces compressive stresses that hinder crack propagation. The synergy between these three sintering aids results in a material with a refined microstructure, reduced porosity, and enhanced resistance to mechanical failure. The high transparency achieved in this study is particularly noteworthy. The combination of high density and fine grain size minimizes light scattering, allowing for efficient transmission of both visible and infrared radiation. This makes the material suitable for applications where optical clarity and mechanical robustness are essential. Furthermore, the enhanced mechanical properties, such as hardness, fracture toughness, and flexural strength, expand the range of potential applications to include demanding environments where resistance to wear, impact, and high stress is critical. The enhanced optical transparency observed in the 100M100L300Z sample can be further explained by the interplay between grain size reduction and porosity minimization. The addition of ZrO₂, in particular, plays a critical role in refining the grain structure, as the tetragonal-to-monoclinic phase transformation induces compressive stresses that inhibit grain growth. This, combined with the stabilizing effect of La₂O₃ on the spinel network and the grain boundary pinning effect of MgO, results in a microstructure with minimal light scattering centers. The uniform distribution of these sintering aids, as confirmed by X-ray mapping, ensures that the material maintains high transparency across both visible and infrared wavelengths. This multi-faceted approach to controlling microstructure is key to achieving the high transmittance values reported in this study. 3.8.Comparison with Previous Studies The fracture toughness of the 100M100L300Z (Z) sample (5.24 MPa·m⁰·⁵, Table 6 ) is superior to values reported for alumina with single or dual sintering aids (e.g., 4.4 MPa·m⁰·⁵ for MgO-Y₂O₃ [ 18 ] and 2.5–3.52 MPa·m⁰·⁵ for pure alumina [ 19 – 21 ]). Similarly, the flexural strength of the Z sample (356.83 MPa) exceeds that of alumina with 0.5 wt.% MgO (322 MPa) [ 24 ]. These results demonstrate the superiority of the triple sintering aid system in enhancing both mechanical and optical properties. Table 6 Parameter Current work [ 12 ] [ 16 ] [ 15 ] [ 3 ] Additives 100 ppm MgO, 100 ppm La₂O₃, 300 ppm ZrO₂ 500 ppm MgO 100 ppm MgO-100 ppm La 2 O 3 450 MgO − 450 Y 2 O 3 -450ZrO 2 100 ppm MgO, 400 ppm Y₂O₃ Fracture Toughness (MPa√m) 5.24 4.8 5.1 4.9 - Flexural Strength (MPa) 356 320 340 310 193 Visible Light Transmission (700 nm, %) 32 28 30 25 13 Infrared Transmission (5 µm, %) 71.4 61 67 68 60 Synthesis Method (SPS) (SPS) (SPS) (SPS) (SPS) The results of this study not only demonstrate the superiority of the triplex sintering aid system but also highlight the potential for further optimization. For instance, the fracture toughness of 5.24 MPa·m⁰·⁵ achieved in this work is significantly higher than that reported in previous studies using single or dual sintering aids. This improvement can be attributed to the synergistic effects of MgO, La₂O₃, and ZrO₂, which collectively enhance grain boundary strength and reduce crack propagation. Furthermore, the flexural strength of 356.83 MPa surpasses that of alumina with 0.5 wt.% MgO (322 MPa) [ 24 ], indicating that the combination of these three sintering aids not only improves optical properties but also significantly enhances mechanical performance. These findings suggest that the triplex sintering aid system could be a promising approach for developing high-performance transparent alumina ceramics for demanding applications such as armor and optical windows. 4. Conclusion In this study, the effects of three sintering aids—magnesia (MgO), lanthanum oxide (La₂O₃), and zirconia (ZrO₂)—on the optical and mechanical properties of transparent alumina ceramics were investigated. The 100M100L300Z (Z) sample, containing 100 ppm MgO, 100 ppm La₂O₃, and 300 ppm ZrO₂, exhibited the highest infrared transmittance (71.4% at 5 µm) and visible transmittance (32% at 750 nm). This sample also demonstrated superior mechanical properties, including a hardness of 19.34 GPa, fracture toughness of 5.24 MPa·m⁰·⁵, and flexural strength of 356.83 MPa. These improvements are attributed to the synergistic effects of the triple sintering aids, which reduce grain size, minimize porosity, and increase densification. The optical properties of the 100M100L300Z sample, particularly its high infrared transmittance (71.4% at 5 µm) and visible transmittance (32% at 750 nm), are a direct result of the combined effects of the triple sintering aids. The reduction in grain size and porosity minimizes light scattering, while the uniform distribution of the sintering aids ensures that the material maintains high transparency across a wide range of wavelengths. The ability to achieve such high levels of transparency while maintaining excellent mechanical properties is a significant advancement in the field of transparent ceramics, opening up new possibilities for applications in optical systems. Declarations Conflict of Interest The authors declare that they have no conflict of interest with any individual, company, or organization concerning this research. Author statement: A.K., M.R., H. J, EM. S, S. T, AN.E and F.D. wrote the main manuscript text and prepared figures. All authors reviewed and edited the manuscript. All authors contributed in interpretation and data gathering and editing manuscript. Acknowledgement Data availability:The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. 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"Effects of the nature of the doping salt and of the thermal pre-treatment and sintering temperature on Spark Plasma Sintering of transparent alumina." Ceramics International 37, no. 8 (2011): 3565-3573. Apak, Burcu, G. Göller, Yücel Onüralp, and Filiz Çinar Şahin. "The effects of codoping Y2O3 on MgO doped spark plasma sintered Al2O3." Advances in Science and Technology 63 (2011): 74-78. Shahbazi, H., M. Tataei, M. H. Enayati, A. Shafeiey, and M. Azizi Malekabadi. "Structure-transmittance relationship in transparent ceramics." Journal of Alloys and Compounds 785 (2019): 260-285. Tyagi, Jyoti, Sanjeev Kumar Mishra, and Shahzad Ahmad. "Transparent ceramics: The material of next generation." In Metal Oxides for Next-Generation Optoelectronic, Photonic, and Photovoltaic Applications , pp. 45-75. Elsevier, 2024. Oparina, I. B., and A. G. Kolmakov. "Methods for obtaining transparent polycrystalline ceramics from aluminum oxide." Refractories and Industrial Ceramics 62 (2021): 196-201. Stuer, Michael, Zhe Zhao, Ulrich Aschauer, and Paul Bowen. "Transparent polycrystalline alumina using spark plasma sintering: effect of Mg, Y and La doping." Journal of the European Ceramic Society 30, no. 6 (2010): 1335-1343. Shahriari, M., H. Jamali, H. Mansouri, M. R. Loghman Estarki, and M. Sardarian. "Fabrication of Spark Plasma Sintered Spark Plasma Sintered Transparent Alumina Using Magnesium Oxide and Lanthanum Oxide as Sintering-Assisted." Journal of Advanced Materials in Engineering (Esteghlal) 41, no. 3 (2022): 31-40. Apak, Burcu, Halide Esra Kanbur, Esra Ozkan Zayim, Gultekin Goller, Onuralp Yucel, and Filiz Cinar Sahin. "Transparent Polycrystalline Alumina Obtained by SPS: Single and Double Doping Effect." Supplemental Proceedings: Materials Processing and Interfaces 1 (2012): 481-487. Boldin, M. S., A. A. Popov, A. A. Murashov, N. V. Sakharov, S. V. Shotin, A. V. Nokhrin, V. N. Chuvil’deev, N. Yu Tabachkova, and K. E. Smetanina. "Investigation of the effect of a small addition of ZrO2 on the density and growth of grains of fine-grained aluminum oxide." Technical Physics 67, no. 7 (2022): 570-580. Ratzker, Barak, Avital Wagner, Sergey Kalabukhov, and Nachum Frage. "Improved alumina transparency achieved by high-pressure spark plasma sintering of commercial powder." Ceramics International 46, no. 13 (2020): 21794-21799. Kuang, Zhong, Ming Yin, Zhuoying Jia, Xiaoqiang Li, and Shengquan Yu. "The preparation of highly transparent alumina ceramics with excellent mechanical performance via co-doping strategy." Journal of Alloys and Compounds (2025): 179497. Pristinskiy, Yuri, Nestor Washington Solis Pinargote, and Anton Smirnov. "The effect of MgO addition on the microstructure and mechanical properties of alumina ceramic obtained by spark plasma sintering." Materials today: proceedings 19 (2019): 1990-1993. Harris, Daniel C. Materials for infrared windows and domes: properties and performance . Vol. 158. SPIE press, 1999. Zhang, Luping, Quan Liu, Dazhao Yu, Mi Lu, and Jianping Lin. "Effect of sintering process on the properties of transparent Al2O3." Materials Science and Technology 39, no. 8 (2023): 926-932. Ratzker B, Wagner A, Sokol M, Kalabukhov S, Dariel MP, Frage N. Optical and mechanical properties of transparent alumina fabricated by high-pressure spark plasma sintering. Journal of the European Ceramic Society. 2019 Jul 1;39(8):2712-9. Additional Declarations No competing interests reported. Supplementary Files mFigsupport20121402Copy.docx Cite Share Download PDF Status: Published Journal Publication published 01 Jul, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 08 Apr, 2025 Reviews received at journal 05 Apr, 2025 Reviews received at journal 04 Apr, 2025 Reviewers agreed at journal 25 Mar, 2025 Reviewers agreed at journal 25 Mar, 2025 Reviewers invited by journal 25 Mar, 2025 Editor assigned by journal 25 Mar, 2025 Editor invited by journal 25 Mar, 2025 Submission checks completed at journal 22 Mar, 2025 First submitted to journal 22 Mar, 2025 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. 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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-6268009","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":434005072,"identity":"edd9ba25-6ee9-4738-a872-e2d7b77efec7","order_by":0,"name":"Amirhossein Karimi shargh","email":"","orcid":"","institution":"Malek Ashtar University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Amirhossein","middleName":"Karimi","lastName":"shargh","suffix":""},{"id":434005073,"identity":"8c0fef8d-499e-4bed-bc5f-33b8c4c99139","order_by":1,"name":"Mazaher Ramazani","email":"","orcid":"","institution":"Malek Ashtar University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Mazaher","middleName":"","lastName":"Ramazani","suffix":""},{"id":434005074,"identity":"8b3aea37-850b-42c4-b3bd-14a5fe9ee13c","order_by":2,"name":"Hossein Jamali","email":"","orcid":"","institution":"Malek Ashtar University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Hossein","middleName":"","lastName":"Jamali","suffix":""},{"id":434005075,"identity":"b2758ce2-5a99-4560-9065-a2ab3d1df800","order_by":3,"name":"Fatemeh Davar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyUlEQVRIiWNgGAWjYBACezBZAcTMUBE2QloMG0DkGbAWxgaitBgcABKMbWA2RAtBYHD8jOHnynl28gzsPOYPGGrsGPikDxDQcibHWPLstmTDBmYeoCOPJTOw8SUQclhagmTjtgMJDGAtbAcY2HgIOez8s+SfjXNgWv4Ro+VG8jHJxgaoFsY2IrQYznh8zLLhWLJhGzNb4YzEvmQeglrs+RObbzbU2Mnz8x/e8OHDNzs5+R4CWuAAHIMJDAyE7BgFo2AUjIJRQAwAAHy1N7GWuqHbAAAAAElFTkSuQmCC","orcid":"","institution":"Isfahan University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Fatemeh","middleName":"","lastName":"Davar","suffix":""},{"id":434005076,"identity":"e64b8564-2b39-486d-b2bd-e3ce0c373236","order_by":4,"name":"Ehsan Mohammad Sharifi","email":"","orcid":"","institution":"Malek Ashtar University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Ehsan","middleName":"Mohammad","lastName":"Sharifi","suffix":""},{"id":434005077,"identity":"d508334e-c4bf-438a-8e81-f39bcbbd0bd5","order_by":5,"name":"Shahab Torkian","email":"","orcid":"","institution":"Malek Ashtar University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Shahab","middleName":"","lastName":"Torkian","suffix":""},{"id":434005078,"identity":"c203d646-e0d9-4b10-8de9-1a8c32145a44","order_by":6,"name":"Alireza Nasr Esfahani","email":"","orcid":"","institution":"Malek Ashtar University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Alireza","middleName":"Nasr","lastName":"Esfahani","suffix":""}],"badges":[],"createdAt":"2025-03-20 09:08:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6268009/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6268009/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-06197-1","type":"published","date":"2025-07-01T15:58:35+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":79896019,"identity":"e39c9f42-ceba-420d-9162-beab0f5b1ade","added_by":"auto","created_at":"2025-04-04 09:04:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":90074,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffraction (XRD) pattern of the as-purchased alumina powder.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/ab17f09123ef1e6193de6ad5.png"},{"id":79897350,"identity":"c0ea620d-50a7-4abf-bf83-6e51ce642301","added_by":"auto","created_at":"2025-04-04 09:20:51","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":178759,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffraction (XRD) patterns of consolidated alumina powders with different amounts of sintering aids.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/60cf63a6f5cc4f1eea98cddb.png"},{"id":79896024,"identity":"d4cfcca8-dcb6-4527-a198-2f6f861c7df3","added_by":"auto","created_at":"2025-04-04 09:04:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1579985,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscopy (SEM) images of the powders: (a, b) pure alumina; (c, d) G sample (50Z100L-100M); (e, f) Z sample (300Z100L-100M).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/15856c3088266225eaa19697.png"},{"id":79896023,"identity":"36bf70f3-c3c0-481d-86ae-97dd91c47d71","added_by":"auto","created_at":"2025-04-04 09:04:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":389155,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sectional field-emission scanning electron microscopy (FESEM) images of samples with different amounts of sintering aids.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/e48ea8bc92c8d579d75cce3b.png"},{"id":79897351,"identity":"4da259f7-eca1-421c-8c2a-a0db1e24dfcb","added_by":"auto","created_at":"2025-04-04 09:20:51","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1324103,"visible":true,"origin":"","legend":"\u003cp\u003eFracture cross-section images of samples with different amounts of sintering aids.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/037f66e713c68431fc992495.png"},{"id":79898071,"identity":"3c4e5c96-81b7-4a7f-83d1-b814a9bcbd06","added_by":"auto","created_at":"2025-04-04 09:28:51","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":687288,"visible":true,"origin":"","legend":"\u003cp\u003eEnergy-dispersive X-ray spectroscopy (EDS) mapping showing the distribution of elements, along with EDS analysis of bulk alumina containing three sintering aids—magnesia, lanthanum oxide, and zirconia—for sample code Z.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/50eb775cc8f016846b7b32c0.png"},{"id":79896873,"identity":"4583ac8c-5092-4de3-949d-d44b86c5bdd7","added_by":"auto","created_at":"2025-04-04 09:12:51","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":385345,"visible":true,"origin":"","legend":"\u003cp\u003eImages of sintered samples with different amounts of sintering aids.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/8ed769607bca892905f5c7de.png"},{"id":79896034,"identity":"0e2b274a-1a88-462e-ad18-ae0f2644a396","added_by":"auto","created_at":"2025-04-04 09:04:51","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":268519,"visible":true,"origin":"","legend":"\u003cp\u003eFlexural strength test results: (A) Stress-strain diagram of the samples.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/7373b1cf2f5461c4268a538b.png"},{"id":79896026,"identity":"cb8de6a7-dc5d-4aa8-8673-4906be78c5a1","added_by":"auto","created_at":"2025-04-04 09:04:51","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":133128,"visible":true,"origin":"","legend":"\u003cp\u003eFlexural strength test results: (A) Stress-strain diagram of the samples.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/9ba8bcce8835894c53df4f54.png"},{"id":86180959,"identity":"4261e44d-8772-4efb-b958-9209c4213438","added_by":"auto","created_at":"2025-07-07 16:23:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6176345,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/630393a4-0275-47d8-b422-cce98f9e269a.pdf"},{"id":79896870,"identity":"41d5b288-8922-4b85-b0e7-75ab941e3c83","added_by":"auto","created_at":"2025-04-04 09:12:51","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1800506,"visible":true,"origin":"","legend":"","description":"","filename":"mFigsupport20121402Copy.docx","url":"https://assets-eu.researchsquare.com/files/rs-6268009/v1/aa49d59eaddcb4d4a016f5ea.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of Simultaneous Addition of Three Sintering Aids: magnesium, lanthanum, and zirconium oxide on the Mechanical and optical properties of Alumina Ceramics fabricated by SPS Method","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAlumina ceramics are highly valued for their exceptional mechanical properties, electrical insulation, and thermal stability, making them suitable for a wide range of industrial applications. Transparent alumina ceramics, in particular, are critical for use in armor, sensors, and advanced optical systems due to their impressive strength, thermal stability, and optical transparency. Alpha-alumina is a prominent material for infrared windows, offering 50\u0026ndash;70% infrared transmission in the 3\u0026ndash;5 \u0026micro;m wavelength range and excellent mechanical properties. However, its low impact resistance and fracture toughness remain significant limitations. These limitations can be addressed by optimizing sintering conditions to reduce temperature and time while maintaining a fine grain structure [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe performance of alumina ceramics can be significantly enhanced through the addition of appropriate sintering aids, particularly dual systems such as MgO-Y₂O₃, MgO-La₂O₃, or MgO-ZrO₂. These systems have been shown to improve density and mechanical properties in transparent alumina [\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In this study, we investigate the combined effects of three sintering aids\u0026mdash;magnesium oxide (MgO), lanthanum oxide (La₂O₃), and zirconium oxide (ZrO₂) \u0026mdash;on the properties of alumina ceramics produced using the SPS method. Achieving high visible and infrared transparency in ceramics requires minimizing light scattering and ensuring that grain sizes are significantly smaller than the incident wavelength. Thus, achieving full density during sintering and preventing excessive grain growth are essential. The choice of sintering method is critical, and the SPS technique is particularly advantageous for producing materials with high density, short sintering times, and fine grain structures [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn addition to sintering strategies, the use of sintering aids can inhibit grain growth, enhance density, and improve mechanical properties. However, the optimal amount of each additive must be carefully selected. Insufficient amounts may fail to achieve the desired optical properties, whereas excessive amounts can lead to porosity or secondary phase formation, thereby reducing transparency. For instance, Ge et al. demonstrated that 100 ppm La₂O₃ improves compactness and bulk density in alumina ceramics, reducing apparent porosity and enhancing mechanical properties [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Similarly, La\u0026sup3;⁺ ions have been shown to curb grain growth, improving both infrared and visible transmission. However, increasing La₂O₃ concentration beyond 100 ppm does not further inhibit grain growth [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eStudies have also shown that triple additive systems, such as MgO-La₂O₃-Y₂O₃, enhance real in-line transmittance (RIT) compared to dual or additive-free systems. This improvement is attributed to the synergistic effects of the triple combination, with MgO playing a pivotal role by creating oxygen vacancies in the alumina structure, which facilitates the incorporation of Y and La atoms [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eApak et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] investigated the effects of Y₂O₃ and MgO on the mechanical properties of alumina, producing transparent ceramics via SPS at 1300\u0026deg;C and 1340\u0026deg;C under 80 MPa pressure for 5 minutes. Their samples achieved densities ranging from 97.1\u0026ndash;99.9%, and higher MgO concentrations (up to 300 ppm) resulted in increased density. Another study examined the influence of MgO on visible transmission at various sintering temperatures (1300, 1500, and 1700\u0026deg;C), finding that 300 ppm MgO at 1300\u0026deg;C yielded the highest transparency [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Additionally, zirconia additives have been shown to refine alumina grain structure, though concentrations above 300 ppm do not further enhance light transmission [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhile extensive research has explored the effects of single and dual sintering aids (e.g., MgO, La₂O₃, and ZrO₂) on the optical and mechanical properties of transparent alumina, no studies have comprehensively evaluated the simultaneous addition of MgO, La₂O₃, and ZrO₂ on the microstructure, light transmission, and the full suite of mechanical properties (e.g., hardness, fracture toughness, and flexural strength) of alumina. This study aims to address this gap by investigating the synergistic effects of a triple sintering aid system on the properties of SPS-processed alumina ceramics.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Synthesis of Precursors and Sintered Samples\u003c/h2\u003e \u003cp\u003eIn this study, α-alumina powder with a particle size of 200 nm and high purity (99.9%) was purchased from US Research Nanomaterials Inc. The chemical precipitation process for the sintering aids involved using magnesium nitrate (Mg(NO₃)₂), lanthanum nitrate (La(NO₃)₃), and zirconium chloride (ZrOCl₂) salts, all sourced from Merck, Germany. Initially, a slurry was prepared by dispersing 2.2 g of nanosized alumina in 50 mL of deionized water. Subsequently, magnesium nitrate, lanthanum nitrate, and zirconium oxychloride were added according to the compositions specified in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. By adding ammonia and adjusting the pH to 9.5, hydroxide ions (Mg\u0026sup2;⁺, La\u0026sup3;⁺, Zr⁴⁺) were precipitated onto the suspended alumina particles. The resulting slurry was dried in an oven at 60\u0026deg;C for 8 hours, followed by calcination at 800\u0026deg;C to convert the hydroxides (Mg(OH)₂, La(OH)₃, and Zr(OH)₄) into their corresponding metal oxides (MgO, La₂O₃, and ZrO₂.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComposition, sample codes, and Archimedes density of samples prepared with different amounts of sintering aids.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZrOCl\u003csub\u003e2\u003c/sub\u003e.8H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003cp\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMg(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003cp\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLa(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003cp\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRelative density (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eppm of sintering aid\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSample code\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.0002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00127\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e98.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100MgO-100La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-50ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eG: 100M-100L-50Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e.0002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e97.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e200 MgO \u0026minus;\u0026thinsp;100 La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-50 ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eH: 200M -100 L-50 Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e.00005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00127\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e98.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100 MgO \u0026minus;\u0026thinsp;100 La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-100 ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eX: 100M -100 L-100Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e.0005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e99.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e200 MgO \u0026minus;\u0026thinsp;100 La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-100 ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eY: 200M -100L-100Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.00156\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00156\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e99.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100 MgO \u0026minus;\u0026thinsp;100 La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-300 ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eZ: 100 M -100 L-300 Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00127\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e96.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100 MgO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e100M\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00127\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e97.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100 MgO \u0026minus;\u0026thinsp;100 La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e100M100L\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.00156\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00127\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e98.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100 MgO \u0026minus;\u0026thinsp;300 ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e100M300Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSample consolidation was performed using a spark plasma sintering (SPS) machine (manufactured by MUT University, Iran) at a temperature of 1350\u0026deg;C, with a heating rate of 50\u0026deg;C/min, under a pressure of 70 MPa for 10 minutes. Graphite molds with a diameter of 2 cm were used for the sintering process.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Characterization Techniques\u003c/h2\u003e \u003cp\u003eX-ray diffractometry (XRD): Performed using an X\u0026rsquo;Pert Pro MPD device (Panalytical, Netherlands) with a copper X-ray tube (wavelength: 1.542 \u0026Aring;), operating at 40 kV and 25 mA. The step size was set to 0.03 degrees.\u003c/p\u003e \u003cp\u003eField emission scanning electron microscopy (FESEM): Structural investigations were performed using an FEI model (USA).\u003c/p\u003e \u003cp\u003eDensity measurements: Evaluated using Archimedes\u0026rsquo; method.\u003c/p\u003e \u003cp\u003eVisible-ultraviolet (UV-Vis) transmission tests: Conducted over a wavelength range of 200\u0026ndash;800 nm using a Ray Leigh UV-1600 device.\u003c/p\u003e \u003cp\u003eInfrared (IR) transmission tests: Investigated using Infralum FT-08 LUMEX infrared spectroscopy.\u003c/p\u003e \u003cp\u003eThree-point bending tests: Performed using a Hounsfield H25KS (England) equipped with a 500 N load cell, moving at a speed of 0.1 mm/min.\u003c/p\u003e \u003cp\u003eMicrohardness testing: Conducted using a 101/642-MiTi model (Mitutoyo, Japan) by applying a 1 kg load for 10 seconds.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Structural and Phase Analysis\u003c/h2\u003e \u003cp\u003eThe X-ray diffraction (XRD) pattern of the initial alumina powder is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The diffraction peaks correspond to α-alumina (JCPDS card no. 01-073-1512), with lattice parameters of a\u0026thinsp;=\u0026thinsp;0.47544 nm and c\u0026thinsp;=\u0026thinsp;1.297 nm, confirming a rhombohedral crystal structure. Using the Williamson-Hall method, the crystallite size of the alumina powder was calculated to be 43.4 nm.\u003c/p\u003e \u003cp\u003eThe XRD patterns of the bulk samples with different sintering aid compositions, after SPS treatment at 1350\u0026deg;C are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Due to the detection limit of XRD (phases below 5 wt.% are not detectable), all samples exhibited diffraction patterns consistent with the α-alumina phase, with no evidence of additional or decomposed phases.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Microstructural Analysis\u003c/h2\u003e \u003cp\u003eScanning electron microscopy (SEM) images of the α-alumina powder with the three sintering aids (MgO, La₂O₃, and ZrO₂) are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The images reveal alumina nanoparticles with sizes ranging from 200 to 250 nm, alongside smaller particles (\u0026lt;\u0026thinsp;100 nm) attributed to the precipitated sintering aids after calcination at 800\u0026deg;C.\u003c/p\u003e \u003cp\u003eEnergy-dispersive X-ray spectroscopy (EDS) analysis of the samples with compositions 100M100L300Z and 100M100L50Z is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The EDS results indicate that the weight percentages of lanthanum, magnesium, and zirconium exceeded the theoretical values due to fluorescence errors inherent in the EDS analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Density and Microstructure\u003c/h2\u003e \u003cp\u003eThe bulk density of all samples, as evaluated by Archimedes\u0026rsquo; method, is summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The results show that the 100M-100L-300Z (Z) sample, with the highest zirconia content (300 ppm), achieved the highest bulk density of 3.94 g/cm\u0026sup3;, corresponding to 99.9% of the theoretical density of α-alumina. This improvement is attributed to the role of zirconia in reducing surface tension and grain boundary energy, thereby enhancing the sintering process and promoting denser microstructures [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan additionalcitationids=\"CR15 CR16 CR17\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe high bulk density (3.94 g/cm\u0026sup3;) achieved in the 100M100L300Z sample is a direct result of the combined effects of the triple sintering aids. The addition of ZrO₂ reduces surface tension and grain boundary energy, promoting densification during the sintering process [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Meanwhile, MgO and La₂O₃ stabilize the microstructure and prevent the formation of pores, further enhancing the density of the material [\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The ability to achieve near-theoretical density in such a short sintering time is a testament to the effectiveness of the triplex sintering aid system, as it allows for the production of high-performance transparent alumina ceramics with minimal defects.\u003c/p\u003e \u003cp\u003eField emission scanning electron microscopy (FESEM) images of the fracture surfaces of the prepared samples are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The 100M-100L-300Z (Z) sample exhibited the smallest grain size and no observable porosity, confirming its superior densification.\u003c/p\u003e \u003cp\u003eThe microstructure of the 100M100L300Z sample, characterized by its fine grain size and lack of observable porosity, is a direct result of the synergistic effects of the triple sintering aids. The addition of ZrO₂ inhibits grain growth through its phase transformation mechanism, while MgO and La₂O₃ stabilize the grain boundaries and prevent the formation of secondary phases. This combination of effects results in a dense, uniform microstructure that is essential for achieving both high optical transparency and mechanical strength. The ability to control grain size and porosity through the use of multiple sintering aids is a key advantage of the triplex system, as it allows for the development of materials with tailored properties for specific applications.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Elemental Distribution\u003c/h2\u003e \u003cp\u003eX-ray mapping of the elemental distribution in the Z sample is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The analysis confirms the uniform distribution of Zr, La, and Mg throughout the alumina grains, indicating the effective incorporation of the sintering aids. The uniform distribution of Zr, La, and Mg is crucial for achieving consistent and predictable material properties. The absence of clustering or segregation suggests that the chemical precipitation method effectively dispersed the sintering aids throughout the alumina grains. This uniform dispersion likely contributes to the enhanced densification and grain growth control observed in the subsequent analyses.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.5. UV-Vis and IR spectra and microstructures\u003c/h2\u003e \u003cp\u003eThe transmission curves for the prepared samples in the visible and infrared ranges are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The 100M-100L-300Z (Z) sample exhibited the highest visible transmittance of 32% at 750 nm and the highest infrared transmittance of 71.4% at 5 \u0026micro;m.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows photographic images of the sintered samples, demonstrating the visible transparency of the Z and Y samples, as evidenced by the clear visibility of the text \"Al₂O₃\" placed behind the samples.\u003c/p\u003e \u003cp\u003eA comparison of the optical results of this study with other reported works is provided in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The infrared transmittance achieved in this work is higher than that of alumina prepared with single sintering aids (e.g., MgO or La₂O₃) or triple sintering aids (e.g., MgO, ZrO₂, and Y₂O₃) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of the optical transmittance of this study with other reported works.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVisible transmission\u003c/p\u003e \u003cp\u003e(at λ\u0026thinsp;=\u0026thinsp;750 nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIR transmission (at λ\u0026thinsp;=\u0026thinsp;5 \u0026micro;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eT/P\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSintering aid content\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1500\u0026deg;C/ 50 MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e450 MgO \u0026minus;\u0026thinsp;450\u003cb\u003eY\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e-450ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1500\u0026deg;C /80MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e500 ppm MgO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1500\u0026deg;C /70MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e100 ppm MgO-100 ppm La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e71.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1350\u0026deg;C /70MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e100 MgO \u0026minus;\u0026thinsp;100 La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-300 ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCurrent work\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e (Supporting Information File 1) shows the visible light transmission spectra of the samples with different sintering aid compositions. The sample without sintering aids exhibited no transmission in the visible region. In contrast, samples containing 100 ppm magnesia (100M), 100 ppm magnesia\u0026thinsp;+\u0026thinsp;100 ppm lanthanum oxide (100M100L), and 100 ppm magnesia\u0026thinsp;+\u0026thinsp;300 ppm zirconium oxide (100M300Z) showed transmission values of 7%, 14%, and 23%, respectively, at a wavelength of 700 nm. Notably, the sample containing all three sintering aids\u0026mdash;100 ppm magnesia, 100 ppm lanthanum oxide, and 300 ppm zirconium oxide (100M100L300Z)\u0026mdash;achieved a transmission value of 29% at 700 nm. These results highlight the critical role of the triple sintering aid system in enhancing the optical transparency of alumina ceramics.\u003c/p\u003e \u003cp\u003eFigure S2 (Supporting Information File 1) presents cross-sectional field emission scanning electron microscopy (FESEM) images of alumina disks with varying sintering aid compositions. Key observations include:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eWithout sintering aids: The alumina grain size grew to 10 \u0026micro;m, with significant intergranular porosity (indicated by arrows).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eWith 100 ppm magnesia (100M): A mixture of coarse grains (10 \u0026micro;m) and finer grains (50 nm) was observed.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eWith 100 ppm magnesia\u0026thinsp;+\u0026thinsp;100 ppm lanthanum oxide (100M100L): The grain size decreased to 4\u0026ndash;5 \u0026micro;m.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eWith 100 ppm magnesia\u0026thinsp;+\u0026thinsp;300 ppm zirconium oxide (100M300Z): The grain size further decreased to 3 \u0026micro;m.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eThe number of pores (indicated by arrows) decreased significantly from Figure S2a to S2d, demonstrating the effectiveness of sintering aids in reducing porosity and refining grain structure.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.6.Mechanical Properties: Microhardness, Fracture Toughness and Flexural Strength\u003c/h2\u003e \u003cp\u003eThe microhardness of the samples was calculated using Eq.\u0026nbsp;1:\u003c/p\u003e \u003cp\u003e(1) \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:H=0.1891\\times\\:\\frac{P}{2\\left({a}^{2}\\right)}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003ewhere:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cem\u003eH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;hardness (GPa),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;applied load (N),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cem\u003ea\u003c/em\u003e\u0026thinsp;=\u0026thinsp;radius of the indentation (mm).\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThe results, presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, show that the 100M100L300Z (Z) sample exhibited the highest microhardness. For fracture toughness, Eq.\u0026nbsp;2 was used:\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eHardness and micro-hardness values of the sintered samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHardness\u003c/p\u003e \u003cp\u003e(GPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMicrohardness\u003c/p\u003e \u003cp\u003e (GPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSample code\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e 018.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e19.36\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eG: 100M-100L-50Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e18.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e18.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eH: 200M -100L-50 Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e16.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX:100M-100L-100Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e17.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e17.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eY: 200M -100L-100Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e19.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e19.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eZ: 100 M -100 L-300 Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e(2) \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{K}_{IC}=K{\\left(\\frac{E}{H}\\right)}^{\\frac{1}{2}}\\left(\\frac{P}{{c}^{\\frac{3}{2}}}\\right)\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003ewhere:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eKIC​ = fracture toughness (MPa\u0026middot;m⁰\u0026middot;⁵),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eK\u0026thinsp;=\u0026thinsp;dimensionless constant (0.0264) [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e],\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eE\u0026thinsp;=\u0026thinsp;elastic modulus (GPa),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eP\u0026thinsp;=\u0026thinsp;applied load (N),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003ec\u0026thinsp;=\u0026thinsp;crack length (mm).\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThe results, summarized in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, demonstrate that the 100M100L300Z (Z) sample achieved the highest fracture toughness. The significant improvement in fracture toughness observed in the 100M100L300Z sample can be attributed to the combined effects of the triple sintering aids. ZrO₂, in particular, plays a key role in enhancing fracture toughness through its phase transformation mechanism, which induces compressive stresses that hinder crack propagation. Additionally, the presence of MgO and La₂O₃ at the grain boundaries stabilizes the microstructure and reduces the likelihood of intergranular fracture. This multi-mechanism approach to improving fracture toughness is a key advantage of the triplex sintering aid system, as it allows for the development of transparent alumina ceramics with both high optical transparency and excellent mechanical performance.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFracture toughness values of the sintered samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK\u003csub\u003eIC\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(MPa.m\u003csup\u003e0.5\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC\u003c/p\u003e \u003cp\u003e(\u0026micro;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSample code\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e192.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eG: 100M-100L-50Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e114.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX:100M-100L-100Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e102.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eY: 200M -100L-100Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eZ: 100 M -100 L-300 Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.6.1.Flexural Strength\u003c/h2\u003e \u003cp\u003eThe three-point bending strength of the samples was calculated using Eq.\u0026nbsp;3:\u003c/p\u003e \u003cp\u003e(3) \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sigma\\:=\\frac{8PL}{\\pi\\:{D}^{3}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003ewhere:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cem\u003eσ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;flexural strength (MPa),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eP\u0026thinsp;=\u0026thinsp;breaking force (N),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cem\u003eL\u003c/em\u003e\u0026thinsp;=\u0026thinsp;distance between supports (mm),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cem\u003eD\u003c/em\u003e\u0026thinsp;=\u0026thinsp;sample diameter (mm).\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThe results, presented in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e9\u003c/span\u003e, show that the 100M100L300Z (Z) sample exhibited the highest flexural strength. This improvement is attributed to the reduction in grain size, lower porosity, and the synergistic effects of the triple sintering aids.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFlexural strength and grain size values of the sintered samples.Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e: Comparison of the properties of this work with other reported studies.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlexural strength\u003c/p\u003e \u003cp\u003e(MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGrain size (\u0026micro;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSample code\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e269\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eG: 100M-100L-50Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eH: 200M -100L-50 Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e220\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX:100M-100L-100Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e188\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eY: 200M -100L-100Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e356\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eZ: 100 M -100 L-300 Z\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe mechanical properties of the 100M100L300Z sample, including its high hardness (19.34 GPa) and flexural strength (356.83 MPa), are a direct result of the synergistic effects of the triple sintering aids. The fine grain size achieved through the addition of ZrO₂, combined with the grain boundary strengthening effects of MgO and La₂O₃, results in a material with superior resistance to deformation and fracture. The reduction in porosity and the uniform distribution of the sintering aids further contribute to the enhanced mechanical performance, making this material suitable for applications requiring both high strength and optical clarity.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.7.Role of Sintering Aids in Transparency and Density\u003c/h2\u003e \u003cp\u003eThe high relative density achieved in the 100M100L300Z (Z) sample corresponds to a reduction in porosity, which is crucial for improving transparency. High porosity levels lead to light scattering due to the significant difference in refractive indices between air (n\u0026thinsp;\u0026asymp;\u0026thinsp;1) and alumina (n\u0026thinsp;\u0026asymp;\u0026thinsp;1.76). This scattering results in the darkening of the ceramic.\u003c/p\u003e \u003cp\u003eThe addition of zirconia (ZrO₂) plays a key role in grain refinement. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and the SEM images, increasing the zirconium salt content reduces grain size of alumina. This effect is attributed to the tetragonal-to-monoclinic phase transformation of zirconia, which induces a 3\u0026ndash;5% volume expansion and inhibits grain growth at alumina grain boundaries [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFurthermore, magnesia (MgO) promotes the formation of a stable MgAl₂O₄ spinel phase at grain boundaries, which also prevents alumina grain growth [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan additionalcitationids=\"CR22 CR23\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The inclusion of lanthanum oxide (La₂O₃) stabilizes the spinel network, further enhancing the microstructure. The synergistic effect of the triple sintering aid system significantly improves the transparency and mechanical properties of alumina.\u003c/p\u003e \u003cp\u003eThe observed improvements in transparency and mechanical properties can be attributed to several factors. The combination of MgO, La₂O₃, and ZrO₂ creates a multi-faceted approach to controlling grain boundary mobility and defect formation. MgO promotes the formation of MgAl₂O₄ spinel, which not only inhibits grain growth but also scavenges impurities. La₂O₃ stabilizes the spinel structure and reduces oxygen vacancies, while ZrO₂'s phase transformation induces compressive stresses that hinder crack propagation. The synergy between these three sintering aids results in a material with a refined microstructure, reduced porosity, and enhanced resistance to mechanical failure.\u003c/p\u003e \u003cp\u003eThe high transparency achieved in this study is particularly noteworthy. The combination of high density and fine grain size minimizes light scattering, allowing for efficient transmission of both visible and infrared radiation. This makes the material suitable for applications where optical clarity and mechanical robustness are essential. Furthermore, the enhanced mechanical properties, such as hardness, fracture toughness, and flexural strength, expand the range of potential applications to include demanding environments where resistance to wear, impact, and high stress is critical.\u003c/p\u003e \u003cp\u003eThe enhanced optical transparency observed in the 100M100L300Z sample can be further explained by the interplay between grain size reduction and porosity minimization. The addition of ZrO₂, in particular, plays a critical role in refining the grain structure, as the tetragonal-to-monoclinic phase transformation induces compressive stresses that inhibit grain growth. This, combined with the stabilizing effect of La₂O₃ on the spinel network and the grain boundary pinning effect of MgO, results in a microstructure with minimal light scattering centers. The uniform distribution of these sintering aids, as confirmed by X-ray mapping, ensures that the material maintains high transparency across both visible and infrared wavelengths. This multi-faceted approach to controlling microstructure is key to achieving the high transmittance values reported in this study.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.8.Comparison with Previous Studies\u003c/h2\u003e \u003cp\u003eThe fracture toughness of the 100M100L300Z (Z) sample (5.24 MPa\u0026middot;m⁰\u0026middot;⁵, Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) is superior to values reported for alumina with single or dual sintering aids (e.g., 4.4 MPa\u0026middot;m⁰\u0026middot;⁵ for MgO-Y₂O₃ [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] and 2.5\u0026ndash;3.52 MPa\u0026middot;m⁰\u0026middot;⁵ for pure alumina [\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]). Similarly, the flexural strength of the Z sample (356.83 MPa) exceeds that of alumina with 0.5 wt.% MgO (322 MPa) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. These results demonstrate the superiority of the triple sintering aid system in enhancing both mechanical and optical properties.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e\u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCurrent work\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAdditives\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e100 ppm MgO, 100 ppm La₂O₃, 300 ppm ZrO₂\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e500 ppm MgO\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e100 ppm MgO-100 ppm La\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e450 MgO \u0026minus;\u0026thinsp;450\u003cb\u003eY\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e-450ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e100 ppm MgO, 400 ppm Y₂O₃\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFracture Toughness (MPa\u0026radic;m)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e5.24\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e4.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e5.1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e4.9\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e-\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlexural Strength (MPa)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e356\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e320\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e340\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e310\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e193\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVisible Light Transmission (700 nm, %)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e32\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e28\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e30\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e25\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e13\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInfrared Transmission (5 \u0026micro;m, %)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e71.4\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e61\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e67\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e68\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e60\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSynthesis Method\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e(SPS)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e(SPS)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e(SPS)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e(SPS)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e(SPS)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe results of this study not only demonstrate the superiority of the triplex sintering aid system but also highlight the potential for further optimization. For instance, the fracture toughness of 5.24 MPa\u0026middot;m⁰\u0026middot;⁵ achieved in this work is significantly higher than that reported in previous studies using single or dual sintering aids. This improvement can be attributed to the synergistic effects of MgO, La₂O₃, and ZrO₂, which collectively enhance grain boundary strength and reduce crack propagation. Furthermore, the flexural strength of 356.83 MPa surpasses that of alumina with 0.5 wt.% MgO (322 MPa) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], indicating that the combination of these three sintering aids not only improves optical properties but also significantly enhances mechanical performance. These findings suggest that the triplex sintering aid system could be a promising approach for developing high-performance transparent alumina ceramics for demanding applications such as armor and optical windows.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this study, the effects of three sintering aids\u0026mdash;magnesia (MgO), lanthanum oxide (La₂O₃), and zirconia (ZrO₂)\u0026mdash;on the optical and mechanical properties of transparent alumina ceramics were investigated. The 100M100L300Z (Z) sample, containing 100 ppm MgO, 100 ppm La₂O₃, and 300 ppm ZrO₂, exhibited the highest infrared transmittance (71.4% at 5 \u0026micro;m) and visible transmittance (32% at 750 nm). This sample also demonstrated superior mechanical properties, including a hardness of 19.34 GPa, fracture toughness of 5.24 MPa\u0026middot;m⁰\u0026middot;⁵, and flexural strength of 356.83 MPa. These improvements are attributed to the synergistic effects of the triple sintering aids, which reduce grain size, minimize porosity, and increase densification.\u003c/p\u003e \u003cp\u003eThe optical properties of the 100M100L300Z sample, particularly its high infrared transmittance (71.4% at 5 \u0026micro;m) and visible transmittance (32% at 750 nm), are a direct result of the combined effects of the triple sintering aids. The reduction in grain size and porosity minimizes light scattering, while the uniform distribution of the sintering aids ensures that the material maintains high transparency across a wide range of wavelengths. The ability to achieve such high levels of transparency while maintaining excellent mechanical properties is a significant advancement in the field of transparent ceramics, opening up new possibilities for applications in optical systems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflict of Interest\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no conflict of interest with any individual, company, or organization concerning this research.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eAuthor statement:\u003c/h2\u003e \u003cp\u003eA.K., M.R., H. J, EM. S, S. T, AN.E and F.D. wrote the main manuscript text and prepared figures. All authors reviewed and edited the manuscript. All authors contributed in interpretation and data gathering and editing manuscript.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eData availability:The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003e\u0026ldquo;The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u0026rdquo;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAkinribide, Ojo Jeremiah, Gadifele Nicolene Mekgwe, Samuel Olukayode Akinwamide, Fehmi Gamaoun, Chamil Abeykoon, Oluwagbenga T. 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Vol. 158. SPIE press, 1999.\u003c/li\u003e\n\u003cli\u003eZhang, Luping, Quan Liu, Dazhao Yu, Mi Lu, and Jianping Lin. \u0026quot;Effect of sintering process on the properties of transparent Al2O3.\u0026quot; \u003cem\u003eMaterials Science and Technology\u003c/em\u003e 39, no. 8 (2023): 926-932.\u003c/li\u003e\n\u003cli\u003eRatzker B, Wagner A, Sokol M, Kalabukhov S, Dariel MP, Frage N. Optical and mechanical properties of transparent alumina fabricated by high-pressure spark plasma sintering. Journal of the European Ceramic Society. 2019 Jul 1;39(8):2712-9.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Alumina, triplex sintering aid, transparency, ceramics, SPS","lastPublishedDoi":"10.21203/rs.3.rs-6268009/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6268009/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the synergistic effects of a novel triplex sintering aid system\u0026mdash;magnesium oxide (MgO), lanthanum oxide (La₂O₃), and zirconium oxide (ZrO₂)\u0026mdash;on the mechanical and optical properties of transparent alumina ceramics fabricated using spark plasma sintering (SPS). The specimens were sintered at 1350\u0026deg;C for 10 minutes under 70 MPa pressure. The sample with the highest zirconia content (sample Z: 100L100M300Z) achieved a bulk density of 3.94 g/cm\u0026sup3;, corresponding to 99.9% of the theoretical density of alumina. This sample exhibited an infrared transmission of 71.4% at 5 \u0026micro;m and a visible transmittance of 32% at 750 nm, surpassing values reported for single or dual sintering aid systems. Mechanical testing revealed a microhardness of 19.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 GPa and a fracture toughness of 5.24 MPa.m⁰\u0026middot;⁵ for sample Z. Additionally, this sample demonstrated the highest flexural strength of 356.83 MPa, attributed to its finer grain size, reduced porosity, and the synergistic effects of the triplex sintering aids. The results demonstrate a promising pathway for producing high-performance transparent alumina ceramics with tailored properties for demanding optical and mechanical applications.\u003c/p\u003e","manuscriptTitle":"Effect of Simultaneous Addition of Three Sintering Aids: magnesium, lanthanum, and zirconium oxide on the Mechanical and optical properties of Alumina Ceramics fabricated by SPS Method","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-04 09:04:46","doi":"10.21203/rs.3.rs-6268009/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-08T06:19:24+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-05T15:58:44+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-04T17:18:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"114223555621011279695588668429610721492","date":"2025-03-26T00:52:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"288560419030789212951702332341582949636","date":"2025-03-25T14:30:59+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-25T12:46:50+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-25T12:42:16+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-03-25T12:39:36+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-22T20:58:58+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-03-22T20:57:55+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a082241b-0eff-4ce3-9e14-b7b8d2f1739a","owner":[],"postedDate":"April 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":46213870,"name":"Physical sciences/Chemistry"},{"id":46213871,"name":"Physical sciences/Engineering"},{"id":46213872,"name":"Physical sciences/Materials science"},{"id":46213873,"name":"Physical sciences/Materials science/Materials for optics"}],"tags":[],"updatedAt":"2025-07-07T16:20:40+00:00","versionOfRecord":{"articleIdentity":"rs-6268009","link":"https://doi.org/10.1038/s41598-025-06197-1","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-07-01 15:58:35","publishedOnDateReadable":"July 1st, 2025"},"versionCreatedAt":"2025-04-04 09:04:46","video":"","vorDoi":"10.1038/s41598-025-06197-1","vorDoiUrl":"https://doi.org/10.1038/s41598-025-06197-1","workflowStages":[]},"version":"v1","identity":"rs-6268009","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6268009","identity":"rs-6268009","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}