Low-Temperature Volume Expansion of LiH: LiT

Abstract

Crystals of LiH: LiT undergo self-damage due to the $\ensuremath{\beta}$-decay of tritium. The low-temperature volume expansion associated with this damage has been investigated theoretically. Twenty-four defects relevant to the damage process have been studied. The results indicate that one of the various species of interstitial lithium is most likely responsible for the expansion, since these defects cause sufficiently large volume expansion to explain the experimental data. The calculations indicate that the ${\mathrm{Li}}_{2}^{+}$ molecular ion is the favored interstitial species. In addition to the volume expansion, ${\mathrm{Li}}_{2}^{+}$ can account for the observed NMR and ESR signals and it may well be the nucleus for subsequent lithium precipitation.