Effect of misfit strain and external electric field on dielectric behavior of epitaxial SrTiO3 thin films

Abstract

Based on a Landau-Ginsburg-Devonshire (LD)-type phenomenological model, the effect of misfit strain and externally applied electric field on dielectric properties of epitaxially single-domain SrTiO3 thin films is investigated by taking into account the existence of two coupled instabilities (ferroelectric and antiferrodistortive). The epitaxy-induced strain may enable the phase of films transform to ferroelectric phase that is impossible for bulk “quantum paraelectric.” At low temperature, the critical tensile strain is in favor of relative high dielectric constant along [100] direction, while the critical compressive strain is useful to that of [001] direction. A high tunability may be obtained by adjusting misfit strain, especially in the vicinity of a structural phase transition. It is also shown that the electric field is facile to induce ferroelectricity in the case of purely structural orthorhombic (SO) phase or tetragonal (ST) phase under reasonable misfit strains when the external electric field is parallel with the order parameter qi. The structural order parameter induced may explain the “weak peak anomaly” phenomenon. Furthermore, the electric field dependence of dielectric responses of different structure phases is also discussed with various misfit strains. Our theoretical results are in good agreement with the experimental ones reported in the literature.