Structural phase transition in a perovskite-type NH₃(CH₂)₃NH₃CuCl₄crystal – X-ray and optical studies

X-ray powder studies and optical studies (polarized microscopic observation and linear birefringence studies) of the crystal NH3(CH2)3NH3CuCl4 are presented. The X-ray powder studies revealed a change of symmetry from orthorhombic room-temperature phase to monoclinic phase above 434 K. A reversible phase transition of the first order at 434 K on heating and 432 K on cooling was observed in birefringence studies. Optical polarized microscopic observation revealed monodomain and multidomain states in the room-temperature orthorhombic phase with domain walls in (110) and (1-10) planes. The hypothetical prototypic phase is expected to be tetragonal. The change of symmetry from orthorhombic to monoclinic and expected domain structure was found above 434 K in the (010) plane.