Dielectric properties and glassy behaviour in the solid-solution ceramics Pb(Zn1/3Nb2/3)O3-PbTiO3-BaTiO3

The dielectric behaviour of the solid-solution ceramics 0.87(Pb1-xLax/2Kx/2)(Zn1/3Nb2/3)O-3-0.8PbTiO(3)-0.05BaTiO(3) with x = 0, 0.04, 0.08 and 0.12, was measured and analysed ill a broad temperature range and at frequencies from 100 Hz to 100 kHz. It was found that the relation between the temperature and the dielectric constant can be well expressed by an exponential function exp(alpha - beta*T) at temperatures much higher than the temperature T-m of the dielectric constant maximum and that there is a super-exponential relation exp[alpha(1) + (T/beta(1))(1+delta)] at temperatures much lower than T-m. This indicates that the glassy behaviour of the materials is different from that of general glasses. The freezing temperature of the polar regions in these materials is distributed over a broad temperature range, which results in dielectric dispersion of the materials at low temperatures. This demonstrates that both the distribution of the freezing temperatures and the process by which the polar regions are produced are associated with the degree of dielectric relaxation of the materials. Therefore, at least two factors, such as delta and beta, are needed to describe the dielectric relaxation of the materials completely. The relation between the logarithm of the frequency and the dielectric constant at low temperatures can be expressed as a linear function for these materials. The frequency dependence of T-m for the materials is analysed using the Vogel-Fulcher relationship omega = omega(0) exp[-T-0/(T-m - T-f)] and a new relationship omega = omega(0) exp[-(T-0/T-m)(p)]. We confirm that the new fit is much better than the Vogel-Fulcher fit.