EFFECT OF MECHANICAL BOUNDARY-CONDITIONS ON PHASE-DIAGRAMS OF EPITAXIAL FERROELECTRIC THIN-FILMS

A phenomenological thermodynamic theory of ferroelectric thin films ep itaxially grow on cubic substrates is developed using a new form of th e thermodynamic potential. which corresponds to the ac tual mechanical boundary conditions of the problem, For single-domain BaTiO3 and PbTi O3 films, the ''misfit-temperature'' phase diagrams are constructed. I t is found that the 2D clamping of the films, apart from a shift of th e temperature of the ferroelectric transition, results in a change of its order. A change of the sequence of the phases and the appearance o f phases forbidden in the bulk crystals are predicted. [S0031-9007(98) 05421-0].