Crystal structure and lattice distortion of γ-NbNxand δ-NbNx

Abstract
By means of neutron diffraction on single crystals the gamma and delta modification of NbNx is studied using samples with approximately the same x=N/Nb approximately=0.85. For the ordered gamma -NbN0.85 it was possible to refine a tetragonal distorted sodium chloride structure model in spite of the occurrence of twinning. The individual mean square displacements of the N and Nb atoms are compared with those of the disordered cubic delta -NbN0.84 and the dynamical components from previous inelastic neutron scattering investigations. For the delta -NbN0.84 single crystal only a small static distortion of the Nb and N sublattices is found. For gamma -NbN0.85 large static contributions to the mean square displacements of the N atoms occur whereas the sublattice of the Nb atoms is nearly undistorted. The group theoretical relationship between the structures of the gamma and the delta phase of NbNx is discussed.

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