SYMMETRY-BREAKING TRANSITIONS IN CSCL-TYPE SOLIDS

The Landau theory of symmetry and phase transitions is applied to the CsCl-type structure to determine the symmetry-allowed second-order phase transitions at the k = 0 and k = (a* + b*) 2 special points. Two distortions of CsCl-type that have been found experimentally, to the rhombohedral LiPb structure and to the orthorhombic AuCd-type structure, were found to meet the conditions of the theory. The AuCd-type was found to allow a further continuous distortion to the monoclinic NiTi structure that plays an important role in the shape memory of this material. © 1990.