Local polar configurations in lead magnesium niobate relaxors

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Abstract
The field dependence of the dielectric response has been measured for lead magnesium niobate relaxors. The frequency dispersion of the temperature of the permittivity maximum, Tmax, was analyzed using the Vogel–Fulcher relationship. The field dependence of the permittivity at various temperatures was also modeled using a phenomenological expansion in the electric field. The activation energy and a softening of the dielectric response were found to be maximum under a small bias. The freezing temperature was found to be minimum near this same bias. These results are interpreted to mean that the moments of the polar clusters do not freeze in random orientations, but rather locally preferred configurations of moments are proposed to exist. Evidence is presented that the scale of these configurations is approximately 100 Å. At higher biases the relaxation mechanism was shut down; consequently, the nonlinear response was stiffened and Tmax increased. The nonlinear response was also found to be maximum near the freezing temperature.