Structural Phase Transitions in CsPbBr₃

Abstract

Structural phase transitions in perovskite-type CsPbBr₃ have been investigated by neutron diffraction method. Phase transitions occur at 88°C and 130°C, which are respectively second and first order. The phase transition at 130°C is caused by condensation of the M₃ mode at the M point of the cubic Brillouin zone, while the one at 88°C results from condensation of the doubly degenerate R₂₅-like mode (Z₉ mode) at the Z point of the tetragonal Brillouin zone. Group theoretical considerations based on these results reveal that the crystal trans-forms from cubic perovskite structure (O_h¹-Pm3m) to tetragonal D_4h⁵-P4⁄mbm at 130°C and further to orthorhombic D_2h¹⁶-Pmbn at 88°C. Possible atomic displacements induced at the phase transitions are obtained from the eigenvectors of the condensing modes.