文摘
The expressions for the spontaneous polar contribution δn i s to the principal values of the refractive index due to the quadratic electro-optic effect in ferroelectrics have been considered within the phenomenological approach taking into account the polarization fluctuations. A method has been proposed for calculating the magnitude and temperature dependence of the root-mean-square fluctuations of the polarization (short-range local polar order) P sh = 〈P fl 2 〉1/2 below the ferroelectric transition temperature T c from temperature changes in the spontaneous polar contribution δn i s (T) if the average spontaneous polarization P s = 〈P〉 characterizing the long-range order is determined from independent measurements (for example, from dielectric hysteresis loops). For the case of isotropic fluctuations, the proposed method has made it possible to calculate P sh and P s only from refractometric measurements. It has been shown that, upon interferometric measurements, the method developed in this work allows calculating P sh and P s directly from the measured temperature and electric-field changes in the relative optical path (the specific optical retardation) of the light. Original Russian Text © P.A. Markovin, V.A. Trepakov, A.K. Tagantsev, A. Deineka, D.A. Andreev, 2016, published in Fizika Tverdogo Tela, 2016, Vol. 58, No. 1, pp. 131–135.