Structure and microwave dielectric properties of Ca0.7Ti0.7La0.3(Al0.3-xGax)O3 ceramics

Microwave dielectric ceramics in the system Ca0.7Ti0.7La0.3(Al0.3-xGax)O-3 were prepared by the mixed oxide route. Powders were calcined at 1200 degrees C and sintered at 1500 degrees 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 mu m, 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, epsilon(r)=45 +/- 0.5, Q x f=39 900 +/- 2000 GHz and tau(f)= + 12 +/- 0.5 ppm degrees C-1; for x=0.2, epsilon(r)=50 +/- 0.5, Q x f=26 400 +/- 1320 GHz and tau(f)=18 +/- 0.5 ppm degrees C-1. Electron diffraction patterns revealed the presence of (112), ((1) over bar 12) and (110) type twins.