Optical properties of ferroelectric (Pb1-xBax)5Ge3O11 for x=0 and 0.02

We report accurate measurements of the temperature dependence of the indices of refraction [n (T)] in ferroelectric single crystals of (Pb1-xBax)5Ge3O11 for x=0 and 0.02. Above the ferroelectric transition temperature Tc, n (T) is linear with temperature. (It had been hoped that the x=0.02 sample would show nonlinear results similar to those observed in BaTiO3.) Analyzing n (T) below Tc in terms of the quadratic electro-optic effect, [(n-2)]ij=k,lgijklPkPl, reveals very large g values, 20-100 times larger than those observed in Pb perovskites. © 1983 The American Physical Society.