Electron–lattice interaction under high-pressure examined by maximum entropy method using single-crystal diffraction†

Abstract

Single-crystal diffraction studies have been conducted up to 50 GPa using synchrotron radiation with diamond anvil cells. Electron density distribution (EDD) analysis has been performed by the maximum entropy method (MEM) using single-crystal diffraction intensity data in order to elucidate the electric conductivity change, electronic state, charge transfer and charge disproportionation with changing pressure. The MEM calculation based on F obs(h k l) shows a much more precise EDD than the difference Fourier synthesis based on F obs(h k l)−F calc(h k l). The radial distribution of the density indicates the enhancement of the electron localization with increasing pressure. The anisotropy in the electric conductivity of FeTiO3 ilmenite has been clarified by the EDD analysis. The MEM analyses clarify the structure transition from the cubic to tetragonal structure of Fe2TiO4 ulvöspinel. The Jahn–Teller distortion is induced from Fe2+ (3d6) at the tetrahedral site at low temperature and high pressure (HP). The electron density analyses at HPs also elucidate the structure changes of KNbO3, PbTiO3 and BaTiO3 ferroelectrics. The static dipole moment can be evaluated by the observed effects and deformation of the site symmetry. †SpecialVolume forAPSWorkshop InternationalWorkshop on Synchrotron High-Pressure Mineral Physics and Materials Science on 6–7 December 2007.