Abstract
Inelastic and elastic neutron-scattering techniques have been used to study the structure and optical hydrogen vibrations of the ordered niobium hydrides in the concentration range and at temperatures between 4 and 250 K. A splitting of the fundamental vibrational modes with an intensity ratio of 2:1 could be observed in the case of the ɛ phase. The neutron vibrational spectra show clearly that this splitting is due to the existence of two inequivalent hydrogen sites rather than H-H coupling effects. This is confirmed by neutron-diffraction data, which show the presence of two hydrogen sites with different distortions of the surrounding niobium tetrahedra. Our results also provide new information on the phase diagram and the anharmonicity of the hydrogen potential in these hydrides.
- Received 14 April 1997
DOI:https://doi.org/10.1103/PhysRevB.57.11115
©1998 American Physical Society