Nonstoichiometry in Bixbyite-Type Vanadium Sesquioxide

Recently,
a metastable bixbyite-type polymorph of vanadium sesquioxide V2O3 has been synthesized from vanadium trifluoride.
During the preparation, a very low oxygen partial pressure was necessary
to prevent oxidation to higher valent vanadium oxides. In order to
provide a quantitative description of the oxidation process, periodic
quantum-chemical calculations at density-functional theory level were
performed to study the thermodynamics of oxygen incorporation into
bixbyite-type V2O3. Different defect structures
for nonstoichiometric phases with the general composition V2O3+x
are discussed, obtained either by
removing single atoms from their respective lattice positions or by
introducing additional atoms into empty lattice sites. We show that
the stoichiometric phase is likely to incorporate excess oxygen into
the empty 16c Wyckoff position under ambient pressure.
Taking into account the equilibrium of nonstoichiometric phases with
the gas phase, we arrive at an estimate of 10–17 bar for the oxygen partial pressure as the upper limit for stabilizing
the stoichiometric phase under reaction conditions.