We carried out an investigation on the symmetry of the tunnel system of H trapped by Zr in b.c.c. Nb. We measured the elastic energy dissipation of two NbZro.0o45Hx single crystals excited with extensional and torsional vibrations along their [100] and [111] directions at frequencies around 40 kHz. Below 40 K at least two processes are observed under (110} shear (c~1-c~2); under other types of stress the intensity of the main contribution is reduced by about a factor of 5, while a smaller peak around 2 K is completely suppressed. Tunnelling over two or four sites in the perturbed region close to the substitutional impurity is considered; the absence or strong reduction of relaxation under [100] shear can be explained by the symmetry of a four site tunnel system.
Four-site tunnelling of H trapped by substitutional Zr in Nb
F Cordero;
1994
Abstract
We carried out an investigation on the symmetry of the tunnel system of H trapped by Zr in b.c.c. Nb. We measured the elastic energy dissipation of two NbZro.0o45Hx single crystals excited with extensional and torsional vibrations along their [100] and [111] directions at frequencies around 40 kHz. Below 40 K at least two processes are observed under (110} shear (c~1-c~2); under other types of stress the intensity of the main contribution is reduced by about a factor of 5, while a smaller peak around 2 K is completely suppressed. Tunnelling over two or four sites in the perturbed region close to the substitutional impurity is considered; the absence or strong reduction of relaxation under [100] shear can be explained by the symmetry of a four site tunnel system.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
