Dielectric and spectral characteristics of lithium tantalate polydomain crystals

Temperature dependences of dielectric properties of the lithium tantalate crystals have been studied in temperature range 25-800°C and frequency range 10 Hz-10 MHz. The existence of dielectric nonlinearity in comparatively weak (in relation to coercive) fields was revealed. Dielectric nonlinearity in polydomain specimens is dictated by two contributions: "normal" and "anomalous" ones. The nature of the "normal" contribution is correlated with general nonlinear dependence between induced polarization and the field at great values of dielectric permittivity. As to the "anomalous" contribution, it is governed by switching processes in ferroelectric phase. A method is offered of the degree of unipolarity evaluation based on recording of the first order Raman spectra in orientation Y(ZZ)X.