NIOBIUM NITRIDE - STABILITY AND INTEGRITY OF THE NBO PHASE

The ordered vacancy Pm3m (''NbO'') structure was identified by Treece et al. as the phase of their pulsed laser deposited thin film samples of niobium nitride. However, the stoichiometric Pm3m phase of NbN is n ot easily reconciled with published local density functional results, which predict a 5% smaller lattice constant than measured and a high e nergy compared with the competing rocksalt phase (which is common and therefore expected to be the stable phase). Here we investigate a poss ible tetragonal instability of the Pm3m structure that might complicat e the interpretation of xray data on the thin films. We also consider the consequences of incorporation of hydrogen into the films. Neither of these aspects is able to resolve the apparent discrepancy. Copyrigh t (C) 1996 Published by Elsevier Science Ltd