The hopping and tunnelling of D that was trapped by Zr substitutional atoms was investigated by means of elastic energy loss measurements. A Nb0.995Zr0.0045Dx monocrystal was excited, in its c’ and c44 modes, at frequencies of between 6.3 and 130kHz and temperatures ranging from 1 to 300K. The results were compared with previous data on the same material, when doped with H, and on Nb1-yTiy(H,D)x. The main peak, at about 150K, which was due to the hopping of D around Zr was accompanied by secondary peaks at lower temperature; as in the case of previously investigated alloys. This indicated that D, as well as H, had 2 distinct points of occupation around the Zr atom. The most striking feature was the isotopic dependence of a narrow peak, at 2K, due to H or D tunnelling. The intensity of the peak for D was more than an order of magnitude higher than that for H. This was explained by assuming a reduction in the tunnelling matrix element in going from H to D. Tunnelling within both 2 and 4 equivalent sites near to the Zr atom was considered.

G.Cannelli, R.Cantelli, F.Cordero, F.Trequattrini, H.Schultz: Journal of Alloys and Compounds, 1995, 231, 274-8