FERROELECTRIC PHASE-TRANSITION IN CS3BI2I9

Single crystals of Cs3Bi2I9 have been grown. Polarized-optical, dielec tric, and calorimetric studies have been performed, along with measure ments of birefringence, and the coefficients of elasticity c(44), and linear expansion alpha over a wide temperature range. It is found that an intrinsic (pseudo-intrinsic) second-order phase transition to the ferroelastic phase takes place at T-0=220.0+/-0.6 K accompanied by a c hange of the crystal symmetry from 6/mmc to 2/m. The transition parame ter depends linearly on the shear strain x(5) and varies with temperat ure according to a power law with exponent beta=0.5. (C) 1997 American Institute of Physics.