Paramagnetic impurity effects in NMR determinations of hydrogen diffusion and electronic structure in metal hydrides. Gd/sup 3 +/ in YH/sub 2/ and LaH/sub 2. 25/

Journal Article · Thu Dec 01 04:00:00 EST 1983 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.28.6227· OSTI ID:5222892

Phua, T; Beaudry, B J; Peterson, D T; Torgeson, D R; Barnes, R G; Belhoul, M; Styles, G A; Seymour, E F.W.

Measurements are reported of the temperature dependence of the proton spin-lattice and spin-spin relaxation times T/sub 1/ and T/sub 2/ in yttrium and lanthanum dihydrides containing controlled levels of gadolinium as low as 50 ppm. The results demonstrate unambiguously that paramagnetic ions in concentrations so low as to have heretofore been regarded as insignificant have marked effects on the magnitude, frequency dependence, and temperature dependence of T/sub 1/ and to a lesser extent on T/sub 2/, and on the electronic structure and hydrogen diffusion parameters derived therefrom. The Gd/sup 3 +/ ion contributes an additional spin-lattice relaxation rate T/sub 1p/, which in these hydrides arises entirely from the dipolar coupling between impurity and proton moments. Proton magnetization is transported to the relaxation centers by spin diffusion at low temperatures and by hydrogen-atom diffusion at intermediate and high temperatures. The rate R/sub 1p/ is directly proportional to Gd-ion concentration at both low and high temperatures, but in the atom diffusion regime R/sub 1p/ is 20--25 times greater than for spin diffusion. The impurity-induced relaxation is shown to have profound effects on the apparent nuclear-nuclear dipolar relaxation rate R/sub 1d/ associated with hydrogen diffusion. At impurity levels as low as 10 ppm Gd, a secondary minimum appears in the temperature dependence of T3exclamation which may be readily misinterpreted in terms of a second motional process with lower activation energy. Even lower impurity levels yield a characteristic ''slope-change'' effect, which may be construed as indicating a change in the activation energy for hydrogen diffusion.

• Research Organization: Ames Laboratory, U.S. Department of Energy and Department of Physics, and Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011
• OSTI ID: 5222892
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 28:11; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
DIFFUSION
ELECTRONIC STRUCTURE
ELEMENTS
FREQUENCY DEPENDENCE
GADOLINIUM
HYDRIDES
HYDROGEN
HYDROGEN COMPOUNDS
IMPURITIES
LANTHANUM COMPOUNDS
LANTHANUM HYDRIDES
MAGNETIC RESONANCE
METALS
NONMETALS
NUCLEAR MAGNETIC RESONANCE
RARE EARTH COMPOUNDS
RARE EARTHS
RELAXATION
RELAXATION TIME
RESONANCE
SPIN-LATTICE RELAXATION
SPIN-SPIN RELAXATION
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
YTTRIUM HYDRIDES