Structure and microwave dielectric properties of Ca _0·7 Ti _0·7 La _0·3 (Al _0·3−x Ga _x )O ₃ ceramics

Microwave dielectric ceramics in the system Ca0·7Ti0·7La0·3(Al0·3−xGax)O3 were prepared by the mixed oxide route. Powders were calcined at 1200°C and sintered at 1500°C for 4 h. High density products, at least 93% theoretical, were obtained for substitutions in the range 0·03⩽x⩽0·20. The microstructures of the ceramics had grain sizes in the range of 4–15 μm, and those with a high level of substitution (0·1–0·2) contained a grain boundary phase rich in Al–Ga. All the samples were orthorhombic in structure (Pbnm). The dielectric properties improved with Ga substitution; for x = 0·03, ϵr = 45±0·5, Q×f = 39 900±2000 GHz and τf = +12±0·5 ppm °C−1; for x = 0·2, ϵr = 50±0·5, Q×f = 26 400±1320 GHz and τf = 18±0·5 ppm °C−1. Electron diffraction patterns revealed the presence of (112), () and (110) type twins.