Abstract
Enhanced relaxor behavior in epitaxial ${\text{PbMg}}_{1/3}{\text{Nb}}_{2/3}{\text{O}}_{3}$ films are investigated. Analysis of the low-frequency intrinsic dielectric response is combined with studies of the response in far-infrared frequency range. The response is interpreted as that of a composite consisting of ``matrix'' and ``dipoles.'' Temperature dependence of the measured effective permittivity is explained by growth of the ``dipolar'' volume fraction on cooling. The dipolar relaxation time spectra are found to contain large fractions of fast relaxators, which increase with decreasing film thickness. This is shown to explain the enhanced relaxor behavior in the films. The peculiar fast dipoles are suggested to be influenced by film-substrate coupling.
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