Site and barrier energy distributions that govern the rate of hydrogen motion in quasicrystalline Ti45Zr38Ni17Hx

The first application of a recent theory linking nuclear magnetic resonance spin-lattice relaxation rates to interstitial atom motion in disordered sy stems is presented. Laboratory and rotating frame relaxation rate data take n as a function of temperature for H-1 moving in quasicrystalline Ti45Zr38N i17H163 are fitted with the new theory, yielding a hydrogen site energy dis tribution of Gaussian shape and width 47 +/-5 meV. The energy barriers for hydrogen motion show a Gaussian distribution of width 50 +/-5 meV, and the difference between the means of the distributions is 0.42 +/-0.01 eV. This is the first time relaxation rates have been analysed to provide informatio n on both hydrogen site energy and barrier energy distributions simultaneou sly. The data are also fitted using an approach popular for disordered syst ems: the integration of the Bloembergen, Purcell, and Pound relaxation theo ry over a distribution of activation energies. The relative merits of this traditional approach and the recent theory in fitting the relaxation data, and also in fitting measurements of the static and magic angle spinning lin ewidths, are discussed. Although the traditional approach can fit all the d ata self-consistently, the theory's unsupported assumptions are undermined by the new approach.