Dielectric properties of Pb(Fe2/3W1/3)O3under pressure

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Abstract
The dielectric properties such as the real epsilon ' and imaginary epsilon " parts of the complex permittivity and the spontaneous polarisation Ps or ceramic Pb (Fe2/3W1/3)O3 with the diffuse phase transition (DPT) were measured under various pressures up to 7 kbar. The value of the critical exponent gamma for the logarithmic plots of the reciprocal epsilon ' versus the reduced temperature above the transition point Tt (or mean Curie temperature theta av) is 1.78. With increasing pressure p, gamma increase, Tt decreases with the pressure coefficient dTt/dp approximately=-4.0 K kbar-1, the maximum values of epsilon ' and epsilon " decrease, and the broadening of the maximum in epsilon ' or epsilon " increases. The temperature and pressure dependence of epsilon ' and Ps is explained in terms of a phenomenological theory using statistical treatments based on a gaussian distribution of the local Curie temperature. The value of the standard deviation sigma describing the intensity of the DPT is 37K, and increases with increasing p. The phase transition becomes more diffused with increasing p. The values of the Curie constant and the hydrostatic electrostrictive constant are estimated as 2.2*10-6 K Fm-1 and 1.74*10-2 m4C-2 respectively.