Site occupation and local modes of hydrogen in V 2N and Ta 2N

Abstract

In this paper, we report the results of neutron inelastic scattering measurements of H and N vibration excitations in (V, Ta) 2NH 0.04. Vibration energies of the hydrogen atoms are ε = 110 and 112 meV for V 2NH 0.04 and Ta 2NH 0.04, respectively. These energy values are consistent with octahedral site occupation. The values of H-vibration energies are practically the same in spite of the fact that the MeH distances are rather different. The relationship between the hydrogen local mode frequency and metal-interstitial atom distance is interpreted in terms of the nearest-neighbor MeH force constantƒ MeH and δr− the discrepancy between interstitial atoms size and an interstices size. It is found that the plot of renormalized frequency ω 0 = ƒ MeH 1 2 versus δr has a general character for all data, no matter what type of crystal lattice or symmetry of interstices the hydrogen atoms occupy.