Microstructure and microwave properties of CaTiO3-LaGaO3 solid solutions

• Published in: Journal of materials science 2005-10, Vol.40 (19), p.5207-5214
• Main Authors: ZHENG, H, DE GYÖRGYFALVA, Gdc Csete, REANEY, I. M
• Format: Article
• Language: English
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Electrotechnical and electronic ceramics; Exact sciences and technology; Technical ceramics
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-005-4414-1

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 (tauf) of LG was -80 ppm/DGC, its permittivity, epsilonr=27 and MW quality factor, Q*fo=97,000 (@5 GHz). As CT concentration increased, tauf and epsilonr increased to +850 ppm/DGC and 160, respectively but Q*fo decreased to ~20,000. Zero tauf was achieved at x D#~ 0.65 with epsilonr approx 47, and Q* fo 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* fo.