Microwave dielectric properties of bismuth-substituted Ba_3.75Nd_9.5Ti₁₇Al_4/3O₅₄ ceramics

Abstract

The impact of bismuth substitution at neodymium (Nd) site in aluminum-replaced Ba_3.75Nd_9.5Ti₁₈O₅₄ ceramics on dielectric constant (ε _r), quality factor (Qf), and temperature coefficient of resonant frequency (τ _f ) has been determined (0.05 ≤ x ≤ 0.2). With appropriate quality factor values (Qf > 5000 GHz), the dielectric constant increased from 74.42 to a maximum of 90.8 and the temperature coefficient of resonant frequency was tailored from approximately +20 ppm/°C to the vicinity of 0 ppm/°C. The X-ray diffraction patterns showed a single phase for all compositions, while the scanning electron microscopy and energy-dispersive spectrometer data confirmed XRD results. Factors, such as bulk density, average polarizability, microstructure, and tolerance factor which were caused by the substitution, were taken into consideration to discuss the microwave dielectric properties’ variation. Within substituting limit, a series of controllable microwave dielectric properties (ε _r = 75.8, Qf = 8994 GHz, τ _f  = 7.2 ppm/°C; ε _r = 79.1, Qf = 7282 GHz, τ _f  = 2.3 ppm/°C; ε _r = 87.07, Qf = 5548 GHz, τ _f  = −8.6 ppm/°C) could be obtained when sintered at 1350 °C for 2 h for x = 0.05, 0.1, and 0.15, respectively.