ELECTRONIC-STRUCTURE AND CHEMICAL BONDING OF DELTA-BI2O3

The band structure of the fluorite-type delta-Bi2O3 was calculated by the linear LMTO methods in the approximation of overlapping atomic sph eres using the basis set of orthogonal orbitals (LMTO-ASA) and by the full-potential LMTO method (LMTO-FP) for two vacancy orientations over a wide range of oxygen concentrations. The calculated parameters of c hemical bonds - the binding energy E(bin) and the pressure of the elec tron-nuclear system - show that the most stable compound is that with two vacancies per unit cell, oriented predominantly along the [111] di rection. The hybrid Bi-O bonds are weak, and mostly the Bi-Bi bonds ar e responsible for the structural stabilization of delta-Bi2O3 The mech anism of the formation of a semiconductor gap in the band structure of delta-Bi2O3 is discussed.