Hydrogen Tunneling in Nb Doped with Impurities

Direct evidence for the existence of the tunnel-split hydrogen states has been obtained from the high-resolution neutron spectroscopic experiments [104, 105, 

It should be noted that low-temperature dynamical processes were also observed for hydrogen trapped by some substitutional impurities (Ti, Zr) in niobium using the internal friction [119, 120] and heat capacity [121] measurements. In particular, the heat capacity of a NbTio os ahoy doped with H(D) shows considerable hydrogen- or deuterium-induced contributions between 0.05 and 2 K [121]. However, the available experimental information is not sufficient to elucidate the microscopic picture of hydrogen motion in these systems. The same also refers to the low-temperature dynamical processes ofhydrogen in b.c.cVandTa [106, 107,122]. 

Neutron scattering studies ofhydrogen dynamics in solid solutions ofhydrogen in a-manganese [123,124] have revealed a remarkable tunneling effect. This is the 

The position of the peak is found to depend strongly on the isotope (HoD) substitution. In fact, for a-MnDg Qj the low-energy peak appears at 1.6 meV. Because of a certain H contamination of the deuterated sample in experiments [124] and the large incoherent neutron scattering cross-section of H, the peaks at both 1.6 meV and 6.4 meV are present in the INS spectra of a-MnDo Q5. As an example of the data. 

The temperature dependences of the integrated intensities of the 6.4 meV and 1.6 meV peaks are well described in terms of the Boltzmann thermal population factors of the split ground-state levels, both for the neutron-energy gain and neutron-energy loss. On the other hand, the observed temperature dependences of the peak intensities differ qualitatively from those expected for phonons or harmonic oscillators [124]. 

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