X-ray diffraction study of the phase transitions in the ferroelectric Pb₅(Cr_1-xAl_x)₃F₁₉ system

Abstract

The phase transition in the ferroelectric Pb₅(Cr_1-xA1_x)₃F₁₉ system with 0⩽x⩽1 has been studied by x-ray powder diffraction as a function of temperature. The transition temperature increases linearly from 285 K for x = 1 to 555 K for x = 0 on heating. This transition is strongly first order for all values of x. The resulting thermal hysteresis leads to a linear dependence of T_c on x over the range 0⩽x⩽0.75 on cooling and displaced about 10 K below that found on heating. The thermal hysteresis and consequent coexistence range of both low and high temperature phases at the transition increase rapidly from x = 0.75 to x = 1.