Neutron spectroscopy was used to study the local vibrations of H interstitials, and H-trapping by N interstitials, in TaN0.006H0.003 and in a N-free TaH0.086 reference sample between 1.4 and 295K. The results for TaH0.086 yielded vibrational energies of E1 = 0.113eV and E2,3 = 0.163eV at 295K, when H was in solid solution; together with a higher energy, E1 = 0.120eV, and essentially unchanged energies, E2,3, at low temperatures (1.4 to 4.2K) when H precipitated as a hydride phase. These energies agreed with previous studies. The results for TaN0.006H0.003 yielded, at 295K and low temperatures, vibrational energies which were identical to those of the N-free sample at 295K. The results showed that the H interstitials were trapped by N at low temperatures, and did not precipitate. They also showed that the trapped H interstitials occupied tetrahedral sites. That is, the same type of site which was occupied in the absence of traps.

Hydrogen Vibrations and Hydrogen Trapping in TaN0.006H0.003. M.Heene, H.Wipf, T.J.Udovic, J.J.Rush: Journal of Physics - Condensed Matter, 2000, 12[28], 6183-90