Electronic Specific Heat of Vanadium Chromium Hydride

Rohy, D. A.; Cotts, R. M.

doi:10.1103/physrevb.1.2484

Cited by 30 publications

(3 citation statements)

References 10 publications

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“…There does not appear to be in the literature a systematic NMR study of diffusion in the VH, system at high concentrations. In the course of investigation of host metal NMR Knight shifts and electronic specific heats [53] A striking feature of diffusion in the LaH, system is that a small increment in x beyond 2 has a liberating influence on all the hydrogen nuclei in the sample. Near 400°K a change in concentration from x = 1.93 to x = 2.03 increases the actual jump frequency by more than a factor of 5000.…”

Section: C) Pulsed Nmrmentioning

confidence: 99%

Hydrogen diffusion studies using nuclear magnetic resonance

Cotts

1972

Ber Bunsenges Phys Chem

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Nuclear magnetic resonance (NMR) techniques have been applied in a considerable number of experimental studies of molecular and atomic motion in solids. In most experiments designed to measure diffusion parameters, the power spectrum of the random variation of local magnetic dipolar fields is determined directly from the data. Data usually consists of measurements of the nuclear spin system longitudinal spin‐lattice relaxation time T1 or the transverse spin‐spin relaxation time T2, or both. From these measurements the frequency of atomic jumps can be calculated. The analysis also yields the value of the activation energy of self‐diffusion for the diffusing atom.Two relatively new NMR techniques, the measurement of the spin lattice relaxation time in the rotating frame, T1ρ, and the direct measurement of the diffusion coefficient by observation of the spin echo decay in the presence of an applied magnetic field gradient, are beginning to be utilized in solid state diffusion experiments, but have not yet been applied to metal hydrides.The theory of the effect of atomic motion on nuclear magnetic dipolar interactions is reviewed as the mechanism responsible for spin relaxation.The relationships between T1, T2, and T1ρ and the time between atomic jumps, τc is discussed. The pulsed‐gradient spin echo technique is outlined for direct measurement of the translational diffusion coefficient.NMR experiments utilizing steady‐state and pulsed techniques for studying diffusion in metal hydrides are described for several transition metals including Sc, Ti, V, Y, Zr, Nb, and Ta. Experiments in La, Th, and U‐hydrogen systems are also reported. Diffusion parameters. including Ea, and A in the Arrhenius relation, τ1 = (A−1) exp (Ea/RT), are reported.

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Section: C) Pulsed Nmrmentioning

confidence: 99%

Hydrogen diffusion studies using nuclear magnetic resonance

Cotts

1972

Ber Bunsenges Phys Chem

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“…Satterthwaite and Toepke [1] also showed that their conceptual idea can be proved in experiment. By 1970, it had already been known (mainly by extended experimental work performed at Bell Telephone Laboratories) that conventional metallic hydrides/deuterides VH 0.5 [4], NbH x (x = 0.88, 0.99), NbD y (y = 0.11, 0.13, 0.79, 0.80) [5], ZrH 2 [6], TiH 2 [6], and, remarkably, LaH 2.45 [7] and dihydride of thorium, ThH 2 [6], are not superconductors. Thus, Satterthwaite and Toepke [1] searched for metallic superhydrides (or, in their words, 'high hydrides') and they found that thorium superhydride, Th 4 H 15 , and its isotopic counterpart Th 4 D 15 , are both superconductors with the transition temperature of T c = 8.0-8.3 K. In addition, they found that a prominent isotope effect in Th 4 H 15 versus Th 4 D 15 phases was not observed [1], which indicates a departure from the expected electron-phonon-mediated mechanism of superconductivity [8,9].…”

Section: Introductionmentioning

confidence: 99%

Resistive transition of hydrogen-rich superconductors

Talantsev

Stolze

2021

Supercond. Sci. Technol.

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Critical temperature, T c, and transition width, ΔT c, are two primary parameters of the superconducting transition. The latter parameter reflects the superconducting state disturbance originating from the thermodynamic fluctuations, atomic disorder, applied magnetic field, the presence of secondary crystalline phases, applied pressure, etc. Recently, Hirsch and Marsiglio (2021 Phys. Rev. B 103 134505, doi: 10.1103/PhysRevB.103.134505) performed an analysis of the transition width in several near-room-temperature superconductors and reported that the reduced transition width, ΔT c/T c, in these materials does not follow the conventional trend of transition width broadening in applied magnetic field observed in low- and high-T c superconductors. Here, we present a thorough mathematical analysis of the magnetoresistive data, R(T, B), for the high-entropy alloy (ScZrNb)0.65[RhPd]0.35 and hydrogen-rich superconductors of Im-3m-H3S, C2/m-LaH10 and P63 /mmc-CeH9. We found that the reduced transition width, ΔT c/T c, in these materials follows a conventional broadening trend in applied magnetic field.

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“…Thus, we were unable to choose a temperature range for testing the fit of our experimental results to the Block-Gruneisen relation for completely ordered V 2 H. A Debye characteristic temperature of 293 ± 10°K was determined from measurements of specific heat in V 2 H between 1.7 and 4.2°K. 4 Matthias 5 has stressed the importance of cubic symmetry and the metallic character of metal carbides or nitrides if they are to exhibit high critical temperatures for superconductivity. While V 2 H is metallic, it does not have cubic symmetry and one might suspect that the critical temperature would be considerably lower than that of vanadium metal (>5°K).…”

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confidence: 99%