Spin-lattice relaxation and mobility of protons in the lattice of the TiV$_{0.8}$Cr$_{1.2}$ alloy

Titanium-vanadium-chromium alloys are promising materials for hydrogen storage. They can absorb up to 3.8 wt% of hydrogen with a variable (depending on the composition) temperature of hydrogen release in a convenient range. This paper reports on the results of investigations of the TiV$_{0.8}$Cr$_{1.2}$H$_{5.29}$ hydride by continuous-wave (cw) and pulsed $^1$H nuclear magnetic resonance spectroscopy. It has been revealed that the hydrogen atoms occupy tetrahedral positions of the face-centered cubic lattice. A model that takes into account the exchange between two states of hydrogen, i.e., mobile hydrogen and hydrogen bound to the lattice, has been proposed for interpreting the temperature dependences of the relaxation times $T_1$ and $T_2$ of $^1$H nuclei. The assumption that the exchange occurs in these alloys has made it possible, in particular, to explain the strong difference between the relaxation times $T_1$ and $T_2$ in the high-temperature range.