Random walk theory of ¹H spin relaxation in TaV₂Hx

Abstract

The theory of nuclear spin relaxation is developed for a random walk model of hydrogen diffusing between interstitial g sites in the cubic C15 AB₂ structure. The theory is applied in analysing the proton relaxation data for low H concentration in TaV₂Hx. The random walk theory results are used to assess the accuracy of a simpler modified Bloembergen-Purcell-Pound model. The temperature dependences of the two rates of jumps between g sites are deduced. The temperature dependence of the rate of jumps between g sites on a hexagon shows Arrhenius behaviour above ~50K and a non-Arrhenius form at lover temperatures. The values of this jump rate are incompatible with the results from the analysis of quasielastic neutron scattering experiments. Possible reasons for this discrepancy are suggested.