Ordering of interstitial nitrogen and oxygen in vanadium near to V8N and V8O

The ordered structure of the V8N subnitride was studied by X-rays, electron diffraction and electron microscopy. V8N exists in two different modifications (α′ and α″). The vanadium sublattice of both phases is pseudo-tetragonal, in reality triclinic, with lattice parameters: αo = bo = 3.114 A, co = 2.994 A, αo = βo = 90.5o ± 0.1o, γo = 90o. The proposed unit cell of α′-V8N has dimensions: a = 2√2 ao, c = 2co and corresponds to V32N4. Doublets of nitrogen atoms occupy two sets of octahedral cavities whose shortest axes are aligned along the x and y directions of the sublattice in an ordered fashion. The α″-V8N phase is a periodically twinned modification of the α′-V8N, the twin plane being of the (001) type. The V8O suboxide has the same structure as the α″-V8N, the sublattice parameters being: ao = bo = 3.11 A, co = 2.994 A, αo = βo = 90.3o ± 0.1o, γo = 90o.