A small angle X-ray scattering study of voids formed in oxygen-doped niobium due to 58Ni + bombardment

Abstract

The small angle X-ray scattering was measured from a series of oxygen-doped Nb single crystals which had been irradiated to 50 displacements per atom at 1050 and 1125 K with 4.0 MeV 58Ni + ions. The diffraction results indicated less perfect ordering of the voids than would have been inferred from earlier transmission electron microscopy observations and this was attributed to a micro-domain structure for the void array. In addition, there was qualitative evidence that a significant portion of the observed small angle scattering resulted from a nearly random component of the microstructure; this was tentatively attributed to intrinsic voids and/or void-oxide complexes in the Nb matrix beyond the near-surface zone damaged by the heavy ion bombardment. This proposal is consistent with the observation of weak small angle scattering from unirradiated Nb-0.006% O single crystals. The mean void size and number density of voids were in fair agreement with published transmission electron microscopy results for Nb-0.006% O, but not in the case of Nb-0.5% O. For the higher oxygen concentration, void number densities lower by a factor of 40–70 were determined from the small angle scattering experiment.