Dielectric dispersion in disordered Pb(In 0.5 Nb 0.5 )O 3 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 ( T ) maximum with increasing frequency. At low frequencies ( f <10 6 Hz) the temperatures of ´ and ´´ maxima follow the Vogel-Fulcher law and the entire ´´ 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.
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Bokov et al. (1999) studied this question.
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