Ferroelectrics with Low-energy Electronic Excitations

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We formulate a general theory of the dielectric response of a lattice with a structural transition and a polarization instability due to a soft-optic mode coupled to low energy electronic excitations by the electromagnetic fields. the electronic excitations considered are in two-limits; those of a low density of free-electrons or those of a low density of strongly localized electrons in the Coulomb-glass phase. The ferroelectric transition in the absence of the electronic-excitations and the low energy dielectric properties are shown to be strongly modified.