The consideration of size-induced ferroelectric-paraelectric phase transitionfor conventional and incipient ferroelectrics thin films with perovskitestructure was carried out in phenomenological theory framework ofGinsburg-Landau-Devonshire. The more general form of surface free energyexpansion that includes intrinsic surface stress tensor, surface piezoelectriceffect and electrostriction as well as quadratic and quartic powers of surfacepolarization has been considered. The analytical expressions for thicknessdependence of transition temperature was derived both for the conventional andincipient ferroelectrics. It was shown that although there is noferroelectricity in the bulk incipient ferroelectrics it appears in thin filmfor the negative extrapolation length that is realized e.g. at positive surfacestress coefficient and negative or zero misfit strain. In our consideration wecame to the conclusion about thickness induced ferroelectricity in incipientferroelectrics KTaO3 at room temperature for the thin enough films. The similarsurface effects can influence strongly on the phase transitions in the thinfilms of another incipient ferroelectrics, SrTiO3.
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