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.