Polar behaviour induced by lithium in potassium tantalate ceramics

Polar behaviour in K1−xLixTaO3 ceramics with x = 0.02, 0.05 and 0.10, processed by the conventional solid state method, is studied by Raman spectroscopy and thermally stimulated depolarization current (TSDC) techniques between 10 and 290 K. The TO1 mode of KTaO3 is revealed to harden in the whole temperature range and to split in the low-temperature range by Li doping. One splitting is observed for x = 0.02 and two consequent splittings are detected for x = 0.05 and 0.10. The temperatures, where TO1 mode splitting occurs, are found to correspond to those of the peaks of TSDC, and hence to the onset of the electric polarization. Such behaviour provides evidence for the order-disorder ferroelectric phase transition induced in KTaO3 by lithium doping, which emerges from deformations of the cubic phase developed on cooling either in one (for x = 0.02) or two steps (for x = 0.05 and 0.10).