LOSS SPECTRA OF PURE AND LA-DOPED MGTIO3 MICROWAVE CERAMICS

Pure and La-doped magnesium titanate (MgTiO3) microwave ceramics were sintered and structurally and dielectrically characterized. Doping provides small inclusions of a second phase found to correspond to the La2Ti2O7 compound. It increases the microwave dielectric loss appreciably and gives rise to three absorption peaks in the submillimeter range assigned to polar phonons of the La2Ti2O7 structure. This assignment was confirmed by a direct reflectivity measurement on La2Ti2O7 ceramics. From the temperature dependence of submillimeter losses in the pure sample, one can estimate that from 1000 down to at least 8 GHz about half of the room temperature losses are intrinsic, i.e., due to two-phonon absorption processes.