Dielectric spectra and Vogel-Fulcher scaling in Pb(In0.5Nb0.5)O3 relaxer ferroelectric

Dielectric dispersion in disordered Pb(In0.5Nb0.5)O-6 crystals was studied. Two dispersion regions were found at 10(3)-10(5) Hz and 10(8)-10(9) Hz at room temperature. The low-frequency relaxation process, which has a very wide distribution of relaxation times, shifts to higher frequency (up to about 10(9) Hz) and becomes narrower in frequency with increasing temperature. It is this relaxation process that is responsible for the temperature shift of the diffused epsilon(T) maximum with increasing frequency. At low frequencies (f < 10(6) Hz) the temperatures of epsilon' and epsilon" maxima follow the Vogel-Fulcher law and the entire epsilon" data set can be scaled using a scaling variable related to frequency by the Vogel-Fulcher law. At f > 10(6) Hz the Vogel-Fulcher law and scaling are also valid, but with different fitting parameters. The results can be described in terms of a phenomenological model implying a wide and smooth spectrum of relaxation times which broadens with decreasing temperature rather than be explained by freezing into the glass state.