Structures and microwave dielectric properties of Ca(1−x)Nd2x/3TiO3 ceramics

Ca(1−x)Nd2x/3TiO3 microwave dielectric ceramics were prepared by the mixed oxide route; powders were calcined at 1100 °C and sintered at 1450–1500 °C. High density, single phase products were obtained for all compositions. Grain sizes ranged from 1 μm to 100 μm. There was evidence of significant discontinuous grain growth in mid range compositions; all ceramics were characterised by complex domain structures. With increasing Nd content there was a evidence of a transition from an orthorhombic Pbnm structure to a monoclinic C2/m structure. This was accompanied by a decrease in relative permittivity (ɛr) from 180 to 78, and decrease in the temperature coefficient of resonant frequency (τf) from +770 ppm K−1 to +200 ppm K−1. The product of dielectric Q value and resonant frequency (Q × f) varied in a grossly non-systematic way, exhibiting a peak at 13,000 GHz in Ca0.7Nd0.2TiO3.