Structural Study of the Ferroelectric Phase Transition in Ca₂Sr(C₂H₅CO₂)₆

Abstract

Crystal structures of Ca₂Sr(C₂H₅CO₂)₆ at sixteen temperatures between −160°C and 150°C have been determined accurately, using an X-ray four circle diffractometer. The occupancies of the three disordered methyl groups in a formula unit, together with the displacements of Sr, Ca and O atoms, vary with temperature in the same manner as the spontaneous polarization which takes a saturated value at −160°C. In contrast to this, one of the other methyl groups is in a state of partial disorder even at −160°C. The major part of the spontaneous polarization is explainable by displacements of Ca–O₆ octahedra relative to Sr ion. Using the result of the thermal expansion along the c-axis measured by the Bond method, it was found that the spontaneous strain was compatible with the equivalent two sublattice model on the basis of the determined crystal structures.