Glassy polarization behavior inK2Sr4(NbO3)10-type ferroelectrics

Abstract

We extend our previous measurements of the temperature dependence of the optic indices of refraction, $n(T)$, of two crystals of the ${\mathrm{K}}_{2}$${\mathrm{Sr}}_{4}$${(\mathrm{N}\mathrm{b}{\mathrm{O}}_{3})}_{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 ${P}_{d}$ is observed far above the ferroelectric transition temperature ${T}_{c}$. However, in these noncubic materials, angular averaging of $n(T)$ need not be done, and so ${P}_{d}$ is obtained rather directly. Below ${T}_{c}$ it is in good agreement with the reversible, spontaneous polarization.