X-Ray Studies on Successive Structural Transitions in RbLiSO₄

Abstract

Space groups and super-lattice structures of five phases of RbLiSO 4 are investigated by X-ray diffraction method. Phase I ( T >204^° C ) is paraelectric ( Pmcn - D 2 h 16 ). The incommensurate phase II (202< T <204^° C ) is characterized by a wave number k z =(2+δ)/5 with δ( T )=0.013(204^° C ) ∼0.137(202^° C ). Phase III takes c =2 c 0 structure which belongs to P 2 1 / c 11- C 2 h 5 , where c 0 is the cell dimension in phase I. The ferroelectric phase IV (166< T <185^° C ) belongs to P 11 n - C s 2 and takes c =5 c 0 super-structure. The I-II transition is 2nd order and the critical exponent is β=0.36 ±0.05, while other three transitions are 1st order ones.