Measurements of strain and the optical indices in the ferroelectric Ba0.4Sr0.6Nb2O6: Polarization effects.

Abstract

We report accurate temperature-dependent measurements of the optic index of refraction, the birefringence, and the strain in the ferroelectric, tungsten-bronze crystal ${\mathrm{Ba}}_{0.4}$${\mathrm{Sr}}_{0.6}$${\mathrm{Nb}}_{2}$${\mathrm{O}}_{6}$. This composition congruently melts, so large homogeneous high-quality crystals can be grown. From the experimental data, it appears that far above the ferroelectric phase transition temperature (${T}_{c}$\ensuremath{\approxeq}88 \ifmmode^\circ\else\textdegree\fi{}C), up to a temperature ${T}_{d}$ (\ensuremath{\approxeq}300 \ifmmode^\circ\else\textdegree\fi{}C), the crystals appear to possess a local, randomly oriented (up or down), polarization ${P}_{d}$. The values of ${T}_{d}$ obtained from the index and completely independent strain measurements are in very good agreement with each other, as are the values of ${P}_{d}$. Various aspects of our understanding of the polarization behavior and other effects in this ferroelectric system are discussed.