Effect of Hydrostatic Pressure on the Phase Transitions of {N(CH3)4}2ZnCl4-xBrxMixed Crystals

Abstract

Single crystals of the solid solution system {N(CH 3 ) 4 } 2 ZnCl 4- x Br x have been prepared in a low x region, and the effect of hydrostatic pressure on the phase transitions were measured for x =0.2 and 0.3. The normal-to-incommensurate phase transition temperatures increase linearly with increasing pressure with the rates of 0.126 K/MPa and 0.129 K/MPa for x =0.2 and 0.3 crystals, respectively. The ferroelectric III phase disappears at about 60 MPa for x =0.2 crystal. On the other hand, phase III is not observed for the x =0.3 crystal both at 0 pressure and at high pressures. The II-IV or III-IV transition temperatures also increases with increasing pressure with the rates of 0.162 K/MPa and 0.153 k/MPa for x =0.2 and 0.3 crystals, respectively. The p - T phase diagrams of the mixed crystals are compared with that of pure {N(CH 3 ) 4 } 2 ZnCl 4 , and discussed.