Site Change of Hydrogen Owing to Lattice Distortion in Niobium Alloys

The site occupancy of hydrogen in Nb alloyed with oversized Ta (atomic radius; \(r_{\text{Nb}}=1.43\) A and \(r_{\text{Ta}}=1.44\) A), Nb0.50Ta0.50H0.021 and Nb0.50Ta0.50H0.053, has been investigated at room temperature by the channelling method utilizing a nuclear reaction 1H(11B,α)αα with a 11B beam of an energy of 2.02 MeV. It was observed that, in both specimens, approximately 100% of H atoms are located at tetrahedral (\(T\)) sites. The half-widths of X-ray reflection lines have been measured for the non-hydrogen-doped Nb0.50Ta0.50 specimens. The half-widths for the Nb0.50Ta0.50 specimens are smaller than those for Nb alloyed with approximately the same concentration of undersized Mo atoms (\(r_{\text{Mo}}=1.36\) A), Nb0.52Mo0.48, and close to the value for pure Nb. This result indicates that, in the Nb0.50Ta0.50 specimens, the lattice is undistorted or very weakly distorted as compared with the Nb0.52Mo0.48 specimens. From the present results on the half-widths and the site occupancy of hydrogen in ...