Structure and microwave dielectric characteristics of Ca1−xNd2x/3TiO3 ceramics

Dense Ca1−xNd2x/3TiO3 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 Pnma was refined in the present ceramics where a minor amount of TiO2 was detected as the secondary phase. The microwave dielectric characteristics were strongly affected by the Nd3+ concentration and the processing conditions. The best combination of microwave dielectric characteristics was obtained for the as-sintered samples with x = 0.39: ɛr = 103, Qf = 15340 GHz and τf = 247 ppm/°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.