DIELECTRIC STUDIES OF FERROELECTRIC PHASE-TRANSITIONS IN PB2XSN2(1-X)P2S6 SINGLE-CRYSTALS

The dielectric constant of Pb2xSn2(I-x)P2S6 single crystals was measured at several frequencies from 0.1 to 100 kHz between 3.7 and 420 K. No phase transition is observed at x=1.0. The ferroelectric-paraelectric phase transition temperature decreases linearly as x increases, but curves slightly around x=0.3 and bends at x=0.61. The lowering of the phase transition with an increase in x is considered to be a result of the motion of the Sn2+ ion. At x=0.61 and 0.66, the relatively large dispersions were interpreted as diffuse phase transitions caused by the fluctuation of the concentration of Pb2+ ions.