SITE OCCUPATION AND LOCAL MODES OF HYDROGEN IN V2N AND TA2N

In this paper, we report the results of neutron inelastic scattering m easurements of H and N vibration excitations in (V,Ta)(2)NH0.04. Vibra tion energies of the hydrogen atoms are E=110 and 112meV for V2NH0.04 and Ta2NH0.04 respectively. These energy values are consistent with oc tahedral site occupation. The values of H-vibration energies are pract ically the same in spite of the fact that the Me-H distances are rathe r different. The relationship between the hydrogen local mode frequenc y and metal-interstitial atom distance is interpreted in terms of the nearest-neighbor Me-II force constant f(Me-H) and delta r- the discrep ancy between interstitial atom size and an interstices size. It is fou nd that the plot of renormalized frequency Omega(0)=f(Me-H)(1/2) versu s delta r has a general character for all data, no matter what type of crystal lattice or symmetry of interstices the hydrogen atoms occupy.