X-Ray Study on the Successive Phase Transitions in Rb₂ZnBr₄

Abstract

The successive phase transitions in Rb₂ZnBr₄ are carefully examined by the X-ray diffraction. At the incommensurate-commensurate phase transition temperature T₂=200 K, supercooling effect is observed together with the thermal hysteresis. Below T₃=108 K, the intensity of the (8 0 0) reflection decreases with decreasing temperature, corresponding to the decrease of the spontaneous polarization in the a-direction. The space group below T₄=80 K is suggested to be C_s²-P1c1 or C_2v⁴-P2cm. The phase transition at T₅=50 K depends on the heating rate.