Structure and microwave dielectric characteristics of Ca_(1-x)Nd_(2x/3)TiO_3 ceramics

摘要

Dense Ca_(1-x)Nd_(2x/3)TiO_3 ceramics with x = 0.30, 0.39 and 0.48 were prepared by a solid-state reaction process, and the crystal structure was determined together with the microwave dielectric characterization. The tilted orthorhombic perovskite structure in space group Pmna was refined in the present ceramics where a minor amount of TiO_2 was detected as the secondary phase. The microwave dielectric characteristics were strongly affected by the Nd~(3+) concentration and the processing conditions. The best combination of microwave dielectric characteristics was obtained for the as-sintered samples with x=0.39: epsilon_r = 103, Qf= 15340 GHz and tau_f = 247 ppm/ deg C. Especially, a sharp decrease of Qf was observed for samples with x=0.39 after annealing in oxygen. Both the dielectric constant and temperature coefficient of resonant frequency of the present ceramics were dependent on the bond valence of the octahedral site. Dielectric loss was significantly affected by the lattice defects and the disordered charge distribution.