Peculiarities of dielectric response of 1:1 family relaxors

A mixed ferroglass phase with coexistence of long and short range order was proposed as the model for quantitative description of the 1:1 family relaxors. Calculations of dielectric response of these relaxors were performed in the random field theory framework. Four and three groups of maxima were obtained in the dielectric permittivity temperature dependence at several frequencies for less and more ordered samples respectively. The frequency dependence of maxima at the lowest temperatures was shown to obey the Vogel-Fulcher (V-F) law, whereas other maxima the Arrhenius law. The peculiar feature of more ordered relaxors was shown to be the proximity of freezing temperature T-g to the temperature of maximum position T-m. Measurement of dielectric response of Pb(Sc0.5Nb0.2Ta0.3)O-3 (PSNT) single crystals revealed two groups of maxima, one at T approximate to 310 K and another at T > 330 K. The frequency dependences of low temperature maxima and high temperature ones were shown to obey the V-F law with T-g = 292.5 K and the Arrhenius law with activation energy 0.49 eV. The comparison of obtained experimental data for PSNT as well as those for two samples of PbSc1/2Ta1/2O3 exhibiting different levels of order with the theory have shown that a mixed ferroglass model with different ratio of long and short range order describes fairly well the main peculiarities of the dielectric response of the 1:1 family relaxors.