Modelling of defects and surfaces in perovskite ferroelectrics

Abstract

AbstractThe results of electronic structure calculations for different terminations of SrTiO3 (100) and (110) perovskite thin films are discussed. These calculations are based on the ab initio Hartree‐Fock (HF) method and Density Functional Theory (DFT). Results are compared with previous ab initio plane‐wave LDA and classical Shell Model (SM) calculations. Calculated considerable increase of the Ti–O chemical bond covalency nearby the surface is confirmed by experimental data. Our quantum chemical calculations performed by means of the intermediate neglect of differential overlap (INDO) method confirm the existence of self‐trapped electrons in KNbO3, KTaO3 and BaTiO3 crystals. The relevant lattice relaxation energies are 0.21 eV, 0.27 eV and 0.24 eV, and the optical absorption energies 0.78 eV, 0.75 eV and 0.69 eV, respectively. We suggest a theoretical interpretation of the so‐called green luminescence (2.2–2.3 eV) in ABO3 perovskite crystals as a result of the recombination of electrons and holes forming the Charge‐Transfer‐Vibronic‐Exciton (CTVE). The calculated luminescence energies for SrTiO3, BaTiO3, KNbO3 and KTaO3 perovskite crystals are in a good agreement with the experimentally observed energies.