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 relax ors. Calculations of dielectric response of these relaxors were performed i n the random field theory framework. Four and three groups of maxima were o btained in the dielectric permittivity temperature dependence at several fr equencies for less and more ordered samples respectively. The frequency dep endence of maxima at the lowest temperatures was shown to obey the Vogel-Fu lcher (V-F) law, whereas other maxima the Arrhenius law. The peculiar featu re of more ordered relaxors was shown to be the proximity of freezing tempe rature 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 a nother at T > 330 K. The frequency dependences of low temperature maxima an d high temperature ones were shown to obey the V-F law with T-g = 292.5 K a nd the Arrhenius law with activation energy 0.49 eV. The comparison of obta ined experimental data for PSNT as well as those for two samples of PbSc1/2 Ta1/2O3 exhibiting different levels of order with the theory have shown tha t a mixed ferroglass model with different ratio of long and short range ord er describes fairly well the main peculiarities of the dielectric response of the 1:1 family relaxors.