Dielectric spectra and Vogel-Fulcher scaling in Pb(In0.5Nb0.5)O-3 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 wi de distribution of relaxation times, shifts to higher frequency (up to abou t 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 frequ encies (f < 10(6) Hz) the temperatures of epsilon' and epsilon" maxima foll ow the Vogel-Fulcher law and the entire epsilon" data set can be scaled usi ng 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 differ ent fitting parameters. The results can be described in terms of a phenomen ological model implying a wide and smooth spectrum of relaxation times whic h broadens with decreasing temperature rather than be explained by freezing into the glass state.