ELECTRONIC BAND-STRUCTURE AND CHEMICAL BONDING IN THE TRANSITION-METAL DIOXIDES

Using the self-consistent LMTO-ASA method we calculated the energy bands and the cohesive energies of TiO2, SnO2, ZrO2, HfO2, and delta-Bi2O3, analyzing the trend in the band gaps and the chemical bond in this series of dioxides. For delta-Bi2O3 - one of the best oxygen ionic conductors- the LMTO calculations shed light on the electronic structure and allow to investigate the stability and energy of vacancy formation. It is shown that the Bi-O bonds are very weak and stabilization of the delta-Bi2O3 structure is mainly due to Bi-Bi bonds. This conclusion correlates with an idea of melting of the oxygen sublattice and is confirmed by the presence of oxygen conductivity. Based on the analysis of calculated values of the cohesive energy it is confirmed that the most stable structure contains two vacancies per unit cell.