NMR Studies of the Hydrides of Disordered and Amorphous Alloys

Abstract

Nuclear magnetic resonance (NMR) spectroscopy has had extensive applications to the characterization of metal-hydrogen systems as is well documented in numerous previous review papers1−7. Structural information on hydrogen site occupancies can be obtained from the NMR lineshapes in the “rigid-lattice” (i. e., immobile nuclei) limit. The hyperfine interactions with conduction electrons can be monitored through Knight shifts (σK) and spin-lattice relaxation time (Tle) contributions. The various nuclear relaxation times are usually very sensitive1−7 to translational diffusion. Under suitable conditions, the hydrogen diffusion constants can be directly measured via various spin-echo techniques2,3,5,6. NMR studies have been conducted on all three hydrogen isotopes (i. e., H, D, and T) as well as many host metal nuclei (e. g., 45Sc, 51V, 89Y, 93Nb, and 139La). Although most attention has been primarily focused upon the binary hydride phases (i. e., TiHx, ZrHx, PdHx, etc.), the hydrides formed by crystalline alloys and interraetallics with nominal stoichiometries A2B, AB, AB2, and AB5 have been the subjects of NMR measurements during the past ten years or so. This interest was mainly stimulated by the potential applications of various ternary hydrides (e. g., TiFeHx, LaNi5Hx, Mg2NiHx) as reversible hydrogen storage systems. However, very few reports of NMR experiments on amorphous hydrides formed from metallic glasses have been published to date 8−16 in spite of the recent proliferation of papers on other aspects of these materials. The relative absence of NMR results for amorphous metal-hydrogen systems is partially due to the rather low sensitivity of the technique (i. e., many spectrometers typically require at least 0.5–1.0g samples — which Is often considered to be quite demanding in the metallic glass preparation field). Furthermore, few NMR experiments had been done for H/M ratios below about 0.1 in any crystalline hydride. In fact, most published NMR results8−15 for the amorphous hydrides have been for samples with hydrogen-to-metal (H/M) atomic ratios around unity.KeywordsNuclear Magnetic ResonanceMetal HydrideSite OccupancyNuclear Magnetic Resonance StudyProton Nuclear Magnetic ResonanceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.