NORMAL VIBRATION MODES AND THE STRUCTURAL PHASE-TRANSITIONS IN CESIUM TRICHLOROPLUMBATE CSPBCL3

The perovskite crystal CsPbCl3 is built up by a three-dimensional chain of PbCl6 octahedra. The symmetry, the compatibility relation and the normal vibration modes of this crystal are studied by using the multiplier representation of group theory along the GAMMA-DELTA-X-Z-M-T-R direction in phase I and along the GAMMA-LAMBDA-Z direction in phase II. The successive structural phase transitions (SPT) in CsPbCl3 at T(c1) = 47-degrees-C, T(c2) = 42-degrees-C and T(c3) = 37-degrees-C are induced by the condensation of the cubic zone boundary mode tau-3 at the M point and the tetragonal zone boundary modes tau-9x and tau-9y at the Z point separately. The interpretation of these successive displacive phase transitions with the normal vibration modes from our study is in good agreement with experimental investigation. A similar result from a previous investigation of layered perovskite RbAlF4, which has a two-dimensional octahedral network, is also compared and discussed.