Energetics of Oxygen Interstitials in Cr and V

Dissolved oxygen in group IIIA-VA (Nb, Ti, Zr, Y) based alloys is a fundamental problem, affecting both mechanical properties and oxidation resistance, yet details of the phenomenon are poorly understood. In these alloys, oxygen is more stable dissolved in the metal than as an oxide-compound. In contrast, alloys based on Ni, Fe, Al and Cr exhibit almost no oxygen solubility. To improve the performance of Nb and Ti based alloys it is necessary to understand the differences in oxygen solubility between these two groups of metals. As a first step we considered the energetics of interstitial oxygen in alpha-V and alpha-Cr. Both of these metals have a BCC structure, yet the oxygen solubility in V is much higher than that in Cr. We obtain total energies, densities of states and population analyses using the CASTEP plane-wave pseudopotential density functional computer code. The differences in the energetics and electronic structures of the two materials, particularly the partial densities of states associated with the interstitial oxygen, are discussed.