Polarization in the cubic phase of BaTIO₃

We have measured, at three different wave lengths, the temperature dependence of the optic index of refraction, n(T), in ferroelectric BaTiO3 for T > Tc (Tc ≡ the cubic to tetragonal transition temperature). n(T) deviates from the high temperature extrapolated value between Tc and ≈ Tc + 180°C. Assuming that these deviations are caused by the quadratic electro-optic effect, and taking its dispersion into account, we obtain, with no adjustable parameters, a root mean square polarization, | P |, vs. temperature in the cubic phase. At T+c, |P| is about 30% to 50% of the value of the reversible spontaneous polarization at T-c. These results are consistent with the recently published infrared studies of BaTiO3 for T>Tc and two proposals for their origin are discussed. © 1982.