Incidence of ferroelectric phase transitions on the electronic structure of potassium niobate

Publisher Website
Google Scholar
Abstract
Molecular cluster predictions for electronic structures of cubic, tetragonal and orthorhombic NbO67- clusters, obtained within the self-consistent-field X alpha framework, are related to the electronic and optical properties of KNbO3 crystals in the cubic, tetragonal and orthorhombic phases. Distortions in electronic state levels and electronic populations induced by atomic displacements from the cubic perovskite positions are examined. Ground state electronic distributions are used to determine the inequivalent populations of oxygen ligands inside the valence band, pictured by local densities of states of O 2p-type. X alpha -cluster ionic charges allow the theoretical determination of the spontaneous polarisation, Ps in ferroelectric phases, and comparison with experimental data shows a rather correct estimation of Ps from cluster computations. The band gap anisotropy and the band edge polarisation potentials are obtained using transition-state calculations. A rough estimation of the anisotropy of the imaginary part of the dielectric constant is obtained from the energies of dipolar-allowed transitions. X alpha results are discussed according to different choices of atomic sphere radii.