Structure, Defects and Microwave Dielectric Properties of Al-Doped and Al/Nd Co-doped Ba4Nd9.33Ti18O54 Ceramics

Abstract Low-loss tungsten-bronze microwave dielectric ceramics are a kind of dielectric materials with potential application value for miniaturized dielectric filters and antennas in 5G communication technology. In this work, a novel Al/Nd co-doping method of Ba4Nd9.33Ti18O54 (BNT) ceramics with a chamical formula of Ba4Nd9.33+z/3Ti18-zAlzO54 (BNT-AN, 0 ≤ z ≤ 2) was proposed to improve the dielectric properties through structural and defect modulation. Together with Al-doped ceramics (Ba4Nd9.33Ti18-zAl4z/3O54, BNT-A, 0 ≤ z ≤ 2) for comparison, the ceramics were prepared by solid state method. It is found that Al/Nd co-doping method has a significant effect on improving the dielectric properties compared with Al doping. As the doping amount z increased, the relative dielectric constant (εr) and the temperature coefficient of resonant frequency (τf) of the ceramics decreased, and the Q×f values of the ceramics obviously increased when z ≤ 1.5. Excellent microwave dielectric properties of εr = 72.2, Q×f = 16480 GHz, and τf = +14.3 ppm/℃ were achieved in BNT-AN ceramics with z = 1.25. Raman spectroscopy and thermally stimulated depolarization current (TSDC) technique were firstly combined to analyze the structure and defects in the dielectric ceramics. It is shown that the improvement on Q×f values were origined from the decrease in the strength of the A-site cation vibration and the concentration of oxygen vacancies (Vö), demonstrating the effect and mechanism underlying for structural and defect modulation on the performance improvement of microwave dielectric ceramics.