Microstructure and microwave dielectric properties of BaNd2Ti4-xAl4x/3O12 ceramics

Using the solid-state ceramic route, BaNd2Ti4-xAl4x/3O12 (0 a parts per thousand currency sign x a parts per thousand currency sign 0.15) ceramics were prepared, and the structure, microstructure, and microwave dielectric properties were investigated. The XRD results suggest the formation of single solid solution phase with orthorhombic structure for all studied compositions (0 a parts per thousand currency sign x a parts per thousand currency sign 0.15) and the unit cell volume decreases linearly with x. The SEM results also show no evidence of secondary phase. A small amount of substitutions improves quality factor (Q x f) and the temperature coefficient of resonant frequency (tau (f) ) but leads to a decrease of the permittivity. The tau (f) value is found to decrease with increasing substitutions because of the declination of tolerance factor (t). And the tau (f) can be adjusted from 79.5 to 38.3 ppm/A degrees C with increment of substitutions. Finally, excellent dielectric properties are achieved as x = 0.1 sintered at 1320 A degrees C for 4 h in air: epsilon(r) = 86.1, Q x f = 9702 GHz, tau (f) = 43.1 ppm/A degrees C. The Q x f value is strongly affected by the annealing process. The samples annealed at 1100 A degrees C for 15 h exhibit the best microwave dielectric properties.