Synthesis and characterisation of La0.4Ba0.6Ti0.6RE0.4O3 (where RE =Y, Yb) ceramics.

La0.4Ba0.6Ti0.6RE0.4O3 (where RE =Y, Yb) powders were synthesised by the mixed oxide route. According to laboratory X-ray diffractometry both compositions are single-phase and can be indexed on the Pm3m space group; however, electron diffraction suggests the occurrence of anti-phase octahedral tilting or 1:1 ordering. Ceramics fired at 1600 ?C for 4 h exhibit an average grain size of ?20_m. Bright field TEM images suggest the occurrence of chemical inhomogeneity in both compositions. The dc conductivities and Raman spectra are similar for both compositions; however, La0.4Ba0.6Ti0.6Y0.4O3 ceramics exhibit ?r ?57, quality factor (Qf)?750 GHz and temperature coefficient of resonance (TCF)?12 ppm/K, whereas La0.4Ba0.6Ti0.6Yb0.4O3 ceramics exhibit ?r ?65, Qf?4500 GHz and TCF?1 ppm/K