PHASE-TRANSITIONS IN FERROELECTRIC-FILMS WITH DIFFERENT DEGREE OF STRUCTURAL PERFECTION

Thin polycrystalline (Ba0.85Sr0.15)TiO3 films were obtained by cathode sputtering onto polished (0001) cuts of sapphire single crystals. The reduction of the degree of structure perfection, i.e., higher values of microdeformations epsilon, root-mean-square static displacements of atoms from their sites, u, and smaller dimensions D of the regions of coherent scattering at lower temperatures resulted in a decrease of d ielectric permittivity K, suppression of its maximum in the vicinity o f the phase transition, and disappearance of dielectric nonlinearity. It is shown that point defects giving rise to static displacements of atoms from their positions lead to a loss of ferroelectric properties of the crystals at u values exceeding 0.019 nm.