Structure and dielectric characteristics of epitaxially strained BaTiO_3 thin films

摘要

The structure and static dielectric permittivity of BaTiO_3 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 com-pressive misfit strain can be grown more easily than those under tensile misfit 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 ε_(33) increases to the maximal value under compressive misfit strain, while the ε_(11/22) reaches to its maximal value under tensile misfit strain. This unsymmetrical dielectric behavior caused by strain is attributed to soft phonons in BaTiO_3 films.