Microstructure and microwave properties of CaTiO3-LaGaO3 solid solutions

The phase assemblage, microstructure and microwave ( MW) properties of xCaTiO(3)-( 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 (tau f) of LG was - 80 ppm/degrees C, its permittivity, epsilon(r) = 27 and MW quality factor, Q* f(o) = 97,000 (@ 5 GHz). As CT concentration increased, tau(f) and epsilon(r) increased to + 850 ppm/degrees C and 160, respectively but Q* f(o) decreased to similar to 20,000. Zero tau(f) was achieved at x approximate to 0.65 with epsilon(r) approximate to 47, and Q* f(o) approximate to 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 approximate to 12.5 angstrom. It is suggested that the presence of second phases in the CT- LG compounds may, in part, be responsible for the deterioration in Q* fo. C (c) 2005 Springer Science + Business Media, Inc.