Nuclear magnetic resonance studies of metal-hydrogen systems

Pulsed nuclear magnetic resonance methods have been used to investigate the properties of various metal-hydrogen systems including ZrH[subscript] x, ScH[subscript] x, NbH[subscript] x, VH[subscript] x etc. For pure dihydride-phase samples of ZrH[subscript] x, the spin-lattice relaxation time T[subscript]1 has been measured as a function of temperature in the temperature range from 10 K to 1300 K at 12.2 MHz and 40 MHz. These measurements show that the activation energy E[subscript] a for hydrogen diffusion first increases smoothly from 0.57 eV/atom at x = 1.58 to 0.63 eV/atom at x = 1.93 and then increases quite rapidly near the stoichiometric limit, reaching 1.06 eV/atom at x = 1.98;T[subscript]1 measurements at temperatures below 300 K reveal that the d-band electronic states are split due to the Jahn-Teller effect. For ZrH[subscript] x samples doped with paramagnetic impurity ions (Mn, Cr, Fe), an additional spin-lattice relaxation rate R[subscript]1 p was observed. The rate R[subscript]1 p increases in the sequence Fe-Cr-Mn and also increases sharply with increasing hydrogen concentration in each case. The former result is consistent with the observation that the tendency towards localized-moment formation in Zr increases in the same sequence, whereas the latter may be accounted for by the anti-trapping behavior of these impurities;For dilute solid solution [alpha]-phase Sch[subscript] x, we measured T[subscript]1 of both [superscript]1H and [superscript]45Sc as a function of temperature to investigate hydrogen diffusion. The activation energy E[subscript] a = 0.54 eV/atom and attempt frequency [nu][subscript] o = 1. x 10[superscript]14 Hz were obtained. The absence of a prefactor anomaly in this dilute system is consistent with the hypothesis that such anomalies in other systems may result from repulsive particle-particle interactions at the saddle point;We have also observed anomalous behavior of the proton spin-lattice relaxation time T[subscript]1 at high temperatures (up to 1300 K) for hydrogen in faced-centered-cubic (fcc) dihydride phases of ZrH[subscript] x, TiH[subscript] x, YH[subscript] x and LaH[subscript] x and in the body-centered cubic (bcc) solid solution phases of NbH[subscript] x, VH[subscript] x and their alloys. In addition to the usual T[subscript]1 minimum, T[subscript]1 decreases sharply at higher temperatures, contrary to the expectation that T[subscript]1 would return to the value T[subscript]1 e determined by the conduction electron contribution to the total relaxation rate. This decrease in T[subscript]1 may have its origin in highly correlated hydrogen motion at high temperature. ftn*DOE Report IS-T-1359. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy