LOCAL LATTICE-DISTORTIONS AROUND INTERSTITIAL OXYGEN IN NIOBIUM

The elastic neutron diffuse scattering has been measured on a quenched NbO0.023 single crystal in the [110BAR] reciprocal plane. Because of the large inelastic contribution due to low-energy phonons, a deconvolution method has been developed which increases the time-of-flight analysis accuracy. The coherent elastic diffuse intensity is composed of a diffuse Huang scattering around the Bragg peaks, a strong maximum near the (1.3 1.3 1.3) position and a coherent diffuse signal in the whole plane. There is no clear evidence for a short-range order between interstitials. The first neighbours of the oxygen interstitials are so strongly repulsed that the usual analytic developments are not justified and the data have been analysed within a simple model assuming that the defects are isolated and considering only the perturbation over the four first neighbouring shells.