Structural effects of Li and Nb codoping in a KTaO3 matrix:: A Raman investigation

Raman investigations on single crystals of K1-xLixTa1-yNbyO3 were performed to identify structural effects arising from the simultaneous presence of off-centre Li and Nb ions in the incipient ferroelectric KTaO3. Two soft-mode transitions were evidenced at 45 K and 30 K in a sample with x=0.0014 and y=0.024 after both zero-field and field cooling. These temperatures are close to the maximum and to the extrapolated Curie temperature for non-relaxing permittivity reported in the same system. A sample with x=0.0028 and y=0.013 displayed a ferroelectric transition just below 30 K only after field cooling, also being consistent with permittivity data.