Structure, defects, and microwave dielectric properties of Al-doped and Al/Nd co-doped Ba4Nd9.33Ti18O54 ceramics

Low-loss tungsten-bronze microwave dielectric ceramics are dielectric materials with potential application value for miniaturized dielectric filters and antennas in the fifth-generation (5G) communication technology. In this work, a novel Al/Nd co-doping method of Ba4Nd9.33Ti18O54 (BNT) ceramics with a chemical 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 (Ba4Nd9.33+z/3Ti18-zAlzO54, BNT-A, 0 <= z <= 2) for comparison, the ceramics were prepared by a 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 (epsilon(r)) and the temperature coefficient of resonant frequency (tau(f)) of the ceramics decreased, and the Qxf values of the ceramics obviously increased when z 1.5. Excellent microwave dielectric properties of epsilon(r) = 72.2, Qxf = 16,480 GHz, and tau(f) = +14.3 ppm/degrees C 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 structures and defects in microwave dielectric ceramics. It is shown that the improvement on Qxf values was originated from the decrease in the strength of the A-site cation vibration and the concentration of oxygen vacancies (V-(O) over dot), demonstrating the effect and mechanism underlying for structural and defect modulation on the performance improvement of microwave dielectric ceramics.

Automated summary

Al/Nd co-doping significantly improves the dielectric properties of low-loss tungsten-bronze microwave dielectric ceramics. With the increase of doping amount, the relative dielectric constant and temperature coefficient of resonant frequency decrease, and the Qxf value increases significantly.