Anomalous proton spin-lattice relaxation at high temperatures in bcc transition-metal--hydrogen solid-solution systems

Journal Article · Wed Nov 01 00:00:00 EST 1989 · Physical Review (Section) B: Condensed Matter; (USA)

DOI:https://doi.org/10.1103/PhysRevB.40.9025· OSTI ID:5304988

Han, J; Lichty, L R; Torgeson, D R; Seymour, E F.W.; Barnes, R G ^[1]; Billeter, J L; Cotts, R M ^[2]

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1. Ames Laboratory United States Department of Energy, and Department of Physics, Iowa State University, Ames, Iowa 50011 (USA)
2. Laboratory of Atomic and Solid State Physics, Clark Hall, Cornell University, Ithaca, New York 14853 (USA)

We report anomalous behavior of the proton spin-lattice relaxation time {ital T}{sub 1} at high temperatures (up to 1000 K) for hydrogen in solution in the bcc metals V, Nb, and Ta and in a Nb-V alloy. Besides the usual {ital T}{sub 1} minimum at intermediate temperatures ({similar to}225 K) characterized by the mean dwell time for hopping, {tau}{sub {ital d}}=exp({ital E}{sub {ital a}}/k{sub B}T), {ital T}{sub 1} again decreases sharply at higher temperatures instead of returning to the value {ital T}{sub 1{ital e}} determined by the conduction-electron contribution to ({ital T}{sub 1}){sup {minus}1}. This decrease is well described by an additional contribution to ({ital T}{sub 1}){sup {minus}1} of the form exp({minus}{ital U}/{ital k}{sub {ital B}}T), where {ital U} is a phenomenological activation energy. We have also measured the temperature dependence of the hydrogen diffusion coefficient {ital D} at high temperatures using an NMR stimulated-echo alternating pulsed-field-gradient technique. Within experimental error {ital D} increases with temperature, {ital D}{proportional to}exp({minus}{ital E}{sub {ital a}}/k{sub B}T), up to at least 820 K, where {ital D}{approx gt}10{sup {minus}4} cm{sup 2}/s. If a deviation from Arrhenius behavior occurs, it is toward higher {ital D} at the highest temperatures. The {ital T}{sub 1} and {ital D} results can be described in terms of a model in which hydrogen motion at high temperatures is controlled by two characteristic times corresponding to mobile and immobile states. Two forms of this model are discussed; however, neither is completely satisfactory. One requires an unusual temperature dependence for the immobile state time, while the other predicts a frequency dependence for {ital T}{sub 1} that is not observed.

• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 5304988
• Journal Information: Physical Review (Section) B: Condensed Matter; (USA), Vol. 40:13; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
NIOBIUM
SPIN-LATTICE RELAXATION
NIOBIUM ALLOYS
DIFFUSION
TANTALUM
VANADIUM
VANADIUM ALLOYS
BCC LATTICES
HIGH TEMPERATURE
HYDROGEN
MATHEMATICAL MODELS
PROTONS
RELAXATION TIME
SOLID SOLUTIONS
SPIN ECHO
TEMPERATURE DEPENDENCE
ALLOYS
BARYONS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CUBIC LATTICES
DISPERSIONS
ELEMENTARY PARTICLES
ELEMENTS
FERMIONS
HADRONS
METALS
MIXTURES
NONMETALS
NUCLEONS
RELAXATION
SOLUTIONS
TRANSITION ELEMENTS
360104* - Metals & Alloys- Physical Properties