| dc.description |
We studied, by neutron spectroscopy, local vibrations of hydrogen interstitials and hydrogen trapping by nitrogen interstitials in TaN<sub>0.006</sub>H<sub>0.003</sub> and in a nitrogen-free TaH<sub>0.086</sub> reference sample between 1.4 and 295 K. The measurements on TaH<sub>0.086</sub> yielded vibrational energies E<sub>1</sub> = (113±1) meV and (doubly degenerate) E<sub>2,3</sub>≃163 meV at 295 K where hydrogen is in solid solution, together with a higher energy E<sub>1</sub> = (120±1) meV and essentially unchanged energies E<sub>2,3</sub> at low temperatures (1.4 to 4.2 K) where hydrogen precipitates in a hydride phase. The energies agree with previous studies. The measurements on TaN<sub>0.006</sub>H<sub>0.003</sub> yielded, at 295 K and at low temperatures, vibrational energies identical to those of the nitrogen-free sample at 295 K. The results show that the hydrogen interstitials are trapped by the nitrogen at low temperatures and do not precipitate. They show further that the trapped hydrogen interstitials occupy tetrahedral sites, i.e. the same type of site as occupied in the absence of traps. |
