The structure and dielectrics of epitaxially strained BaRO 3 (R=Ti, Zr) thin films

Abstract

The structure and static dielectric permittivity of BaRO 3 (R=Ti, Zr) thin films as a function of epitaxial strain are determined by using first-principle density functional theory calculation based on pseudopotentials and a plane-wave basis. It is found that BaTiO 3 thin films under compressive misfit strain can be grown more easily than those under tensile misfit strain, while thin films of BaZrO 3 can be grown more easily under tensile strain. The static dielectric permittivity of BaTiO 3 thin films under different misfit strain is obtained by calculating optical phonon frequencies and Born effective charges using density functional perturbation theory. The zero-temperature dielectric permittivity of e 33 increases to the maximal value under compressive misfit strain, while the e 11/22 reaches to its maximal value under tensile misfit strain. For BaZrO 3 thin films, the dielectric permittivity e r changes little. However, e r exhibits non-linear characteristics under tensile strain, which reaches to the maximal value under misfit strain of ~1%. This unsymmetrical dielectric behavior caused by strain is attributed to soften phonons in BaTiO 3 or BaZrO 3 thin films.