Enhanced quality factor of CaMo_1-xTe_xO₄ ceramics by Te⁶⁺ substitution

Microwave dielectric properties of CaMo1-xTexO4 (0.01 <= x <= 0.05) ceramics were investigated based on the crystal structure characteristics. For the specimens sintered at 900-985 C-degrees for 2 h, a single phase of scheelite structure was confirmed up to x = 0.03, and then secondary phases were observed for further substitution. With an increase in Te6+ content, the quality factor (Qf) of the sintered specimens increased up to x = 0.03 (Qf = 185,500 GHz) and then decreased. The amelioration in the Qf up to x = 0.03 is due to the increase in the B-site bond valence of ABO(4); however, the degradation of the Qf above x = 0.03 could be attributed to the formation of secondary phases. With an increase in Te6+ content, the dielectric constant (K) of the specimens increased from K = 10.42 to K = 10.78 due to the higher polarizability of Te6+ (3.7 angstrom(3)) than that of Mo6+ (3.28 angstrom(3)). As the Te6+ content increased, the temperature coefficient of resonant frequency (TCF) decreased with an increase in oxygen bond valence. Excellent microwave dielectric properties (Qf = 185,500 GHz, K = 10.62, TCF = -36.53 ppm/C-degrees) were obtained for the CaMo0.97Te0.03O4 ceramics which could be applicable to various microwave communication systems.