DYNAMIC EVIDENCE OF HYDROGEN SUBLATTICE MELTING IN METAL-HYDROGEN SYSTEMS

Measurements of the temperature dependence of the proton and deuteron spin-lattice relaxation time T//1 in cubic fluorite (CaF//2) structure dihydrides and dideuterides (MH//2 and MD//2) show a second high temperature turndown in T//1 in addition to the usual minimum associated with the independent hopping motion of H(D) among tetrahedral (T) interstitial sites at lower temperatures. The close analogy to the motion of anions in fluorite structure superionics suggests that the high temperature minimum indicates the onset of strongly correlated hydrogen motion, possibly accompanied by the occurrence of long-lived hydrogen clusters.