Brillouin study of the hexagonal—orthorhombic phase transition in LiKSO 4

Brillouin spectra of lithium potassium sulfate have been obtained in its hexagonal phase from room temperature to the orthorhombic phase transition temperature at 435°C. The ν 11 longitudinal sound velocity corresponding to the C 11 elastic coefficient undergoes a smooth decrease with increasing temperature; the maximum decrease is 6.0% at T 0 =435°C and the temperature dependence of ν 11 satisfies an expression of form\documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{V_{11} (T)}}{{V_{11} (293\,{\rm K})}} = A - BT - \frac{C}{{T_c - T}} $$\end{document}with B =(1.13±0.04) × 10 −4 K −1 , C = (0.9±0.1) K and T c = (467±6)°C=(740±6)K.