Microstructure and microwave properties of {CaT{i}O}3–LaGaO3 {solid solutions}

The phase assemblage, microstructure and microwave (MW) properties of xCaTiO3-(1-x)LaGaO3 (CT-LG) ceramics prepared by solid state synthesis from raw oxides and carbonates have been investigated. LG was predominantly single phase perovskite with space group, Pnma, but a small quantity of pyrochlore structured La2Zr2O7 second phase was present due to the contamination from the ZrO2 milling media. At MW frequencies, the temperature coefficient of resonant frequency (τ{f}) of LG was --80~ppm/ $${\circ}$$ C, its permittivity, $$\varepsilon_r {=} $$ 27 and MW quality factor, $$Q^*f_o {=} $$ 97,000 (@5~GHz). As CT concentration increased, $$\tau_f$$ and $$\varepsilon_r$$ increased to $+$850~ppm/ $$^\circ$$ C and 160, respectively but $$Q^*f_o$$ decreased to $$\sim $$ 20,000. Zero $$\tau_f$$ was achieved at $$x {\approx} $$ 0.65 with $$\varepsilon_r {\approx} $$ 47, and $$Q^*f_o {\approx} $$ 40,000, properties comparable with commercial compositions. However, for $$x {=} $$ 0.5, a different second phase was observed which was rich in Ca and Ga. Electron diffraction patterns could be indexed according to a body centred cubic lattice, $$a {\approx} $$ 12.5 A. It is suggested that the presence of second phases in the CT-LG compounds may, in part, be responsible for the deterioration in $$Q^*f_o$$ .