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 SrTiO ₃. 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 SrTiO ₃ 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).