The geometry and dynamics of the tunnel systems of H trapped by substitutional atoms in Nb has been studied by anelastic spectroscopy on very diluted NbZr (H/D) alloys (x,y,0.0015). At such low impurity levels the features of the anelastic spectrum of the nearly non-interacting complexes are observable, and finally provide clear evidence of the delocalization of H in centrosymmetric four-level systems (FLS). An additional process is found at liquid He temperatures, besides that present also at higher concentrations, and similar to the anelastic response of a two-level system. The new process has an intensity that does not vanish for small asymmetries and a slow rate dominated by two-phonon transitions. Such features can be easily explained in terms of a simple perturbative approach, in which the transitions with the intermediate energy levels of a FLS turn out to be prohibited in the first order.
Tunneling of H within nearly undistorted substitutional-H pairs in Nb: a centrosymmetric four-level system
F Cordero;A Paolone;
2002
Abstract
The geometry and dynamics of the tunnel systems of H trapped by substitutional atoms in Nb has been studied by anelastic spectroscopy on very diluted NbZr (H/D) alloys (x,y,0.0015). At such low impurity levels the features of the anelastic spectrum of the nearly non-interacting complexes are observable, and finally provide clear evidence of the delocalization of H in centrosymmetric four-level systems (FLS). An additional process is found at liquid He temperatures, besides that present also at higher concentrations, and similar to the anelastic response of a two-level system. The new process has an intensity that does not vanish for small asymmetries and a slow rate dominated by two-phonon transitions. Such features can be easily explained in terms of a simple perturbative approach, in which the transitions with the intermediate energy levels of a FLS turn out to be prohibited in the first order.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
