Strain effect on dielectric property of SrTiO3 lattice: first-principles study

We performed first-principles calculations and obtained information on dielectric response and zone center optical phonon of strained SrTiO3. The dielectric response and zone center optical phonon of SrTiO3 lattice under a strained state are calculated by density functional theory within the local density approximation. After the structural analysis SrTiO3 lattice, the zone center optical phonon frequency was calculated by the frozen phonon method. The first-principles calculation showed that lattice distortion strongly affects the lattice dynamic property (e.g., optical phonon) and dielectric property of the strained SrTiO3 lattice. As the SrTiO3 lattice was progressively distorted from unstrained state to c/a=0.985, the optical phonon frequency was softened. As a result, the dielectric constant increased and reached 960. When the SrTiO3 layer was deformed further over c/a=0.985, the dielectric constant decreased again. Therefore, the first-principles calculation showed that a maximum dielectric constant exists at a certain degree of lattice distortion (c/a=0.985), which leads to good agreement with experimental results (i.e., the dielectric behavior of strained SrTiO3 lattice).