Temperature and pressure dependence of dielectric properties of Pb(Fe1/2Nb1/2)O3 with the diffuse phase transition

Abstract

The temperature T (30-150 degrees C) and pressure p (0-6 kbar) dependence of the dielectric properties (relative permittivity in r, dielectric loss tangent and spontaneous polarisation) of ferroelectric Pb(Fe1/2Nb1/2)O3 ceramics synthesised by the use of alkoxides are presented. The relative permittivity in r has a broad maximum at the ferroelectric transition temperature Tt. The results also showed that at T>Tt, (1/ in r-1/ in r max) is proportional to (T-Tt)gamma , where in r max is the peak value of in r at Tt and gamma is a constant. The value of the exponent gamma was found to be equal to 2.0 and remained almost independent of the applied pressure. With increasing pressure, p, the values of both Tt and in r max were reduced. In the case of Tt the reduction was linear with dTt/dp=-3.7 K kbar-1. With increasing DC bias fields Ed, the maximum value of in is lowered, the shape of its curve becomes more rounded and Tt is displaced towards higher temperatures with dTt/dEd=0.7 K cm kV-1. The temperature and pressure dependence of the permittivity and the spontaneous polarisation is explained in terms of a phenomenological theory.