Glassy polarization behavior in K2Sr4 (NbO3)10-type ferroelectrics

We extend our previous measurements of the temperature dependence of the optic indices of refraction, n(T), of two crystals of the K2Sr4(NbO3)10 type with different amounts of disorder. These materials are axial ferroelectrics with the tetragonal tungsten-bronze crystal structure. As in other ferroelectrics where the translational symmetry is strongly broken, a glassy polarization Pd is observed far above the ferroelectric transition temperature Tc. However, in these noncubic materials, angular averaging of n(T) need not be done, and so Pd is obtained rather directly. Below Tc it is in good agreement with the reversible, spontaneous polarization. © 1984 The American Physical Society.