Growth of niobium single crystals by a pedestal method

Abstract

Niobium single crystals of very high perfection were grown by a pedestal method with electron beam bombardment. The quality of the single crystals was assessed by taking both projection and section X-ray topographs with [ 1 01], [10 1 ], [020] and [0 2 0] reflections. Elastic lattice distortions were identified by the change of image contrast which depends on the diffraction vector. No dislocation images were observed around the lattice distortions near a blob of scum on the surface, implying that larger stresses are necessary in bcc crys als than in fcc crystals to generate dislocations. Elastic lattice distortions which originate from planar defects were still present in the bottom part of the crystal. However, no dislocation images were observed in this region. Some comments are given on how to improve the growth conditions in order to grow more perfect niobium crystals.