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Journal ArticleDOI

Electrical resistivity studies on ZrxTb1-xFe3 (x = 0.2, 0.3) hydrides

07 May 2001-Journal of Physics: Condensed Matter (IOP Publishing)-Vol. 13, Iss: 18, pp 4155-4164
TL;DR: In this paper, the authors studied the hydrogen absorption in Zr0.2Tb0.8Fe3 and Zr 0.3Tb 0.7Fe3-H systems on a basis of the combined effects of depopulation of conduction electrons and formations of various phases.
Abstract: The hydrogen absorption isotherm at 30 °C in the range 0.2≤P (bar) ≤20 for Zr0.2Tb0.8Fe3 and Zr0.3Tb0.7Fe3 shows the presence of α, (α + β) and β phases. The study of the kinetics of hydrogen absorption in Zr0.2Tb0.8Fe3 at 30 °C as a function of pressure in the range 8≤P (bar) ≤50 shows the presence of different phases. The dependence of the electrical resistivity (ρ) on the hydrogen concentration in the Zr0.2Tb0.8Fe3-H and Zr0.3Tb0.7Fe3-H systems is discussed on a basis of the combined effects of depopulation of conduction electrons and formations of various phases, namely α, α + β and β. Changes in the slopes of the plots of ρ against y indicate the different phase regions.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the structural and electrical properties of ZrCrFe 0.5 Co 0.83 and 57 Fe Mossbauer spectroscopy characterization have been studied at room temperature.

5 citations

Journal ArticleDOI
TL;DR: In this paper, an experimental facility has been developed to measure the in situ electrical resistivity of alloys during the hydrogen absorption process, which can be explained using the phase transformation during hydrogen absorption.
Abstract: Powder x-ray diffraction and the electrical resistivity of (Ti 0.1 Zr 0.9 ) 1.1 Mn 0.9 V 0.1 Fe 0.5 Ni 0.5 -H x with different hydrogen concentrations have been investigated and the results have been discussed. An experimental facility has been developed to measure the in situ electrical resistivity of alloys during the hydrogen absorption process. Variation in in situ electrical resistivity with hydrogen concentration in (Ti 0.1 Zr 0.9 ) 1.1 Mn 0.9 V 0.1 Fe 0.5 Ni 0.5 has been explained using the phase transformation during hydrogen absorption. Differential scanning calorimetry (DSC) studies have been performed in (Ti 0.1 Zr 0.9 ) 1.1 Mn 0.9 V 0.1 Fe 0.5 Ni 0.5 -H x with different hydrogen concentrations in the temperature range 50-250 °C under argon atmosphere. The DSC studies show that the desorption of hydrogen is from the 24l (A 2 B 2 ) tetrahedral sites. The activation energies and diffusion coefficients of hydrogen in (Ti 0.1 Zr 0.9 ) 1.1 Mn 0.9 V 0.1 Fe 0.5 Ni 0.5 have been determined in the range 30-100°C from the hydrogen absorption kinetics measurements. The diffusion coefficient of hydrogen in (Ti 0.1 Zr 0.9 ) 1.1 Mn 0.9 V 0.1 Fe 0.5 Ni 0.5 -H x at 30°C is 1.1 x 10 -10 cm 2 s -1 .

4 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the first few hydriding-dehydriding cycles, referred to as activation, are discussed and new H 2 -D 2 isotope scrambling results are presented which indicate that metallic iron does not play a catalytic role.
Abstract: The processes involved in the first few hydriding-dehydriding cycles, referred to as activation, are discussed. The controversial activation of TiFe is reviewed and new H 2 -D 2 isotope scrambling results are presented which indicate that metallic iron does not play a catalytic role. The hydriding-dehydriding kinetics are resolved into three interacting processes: intrinsic kinetics, heat flow and mass flow. The intrinsic kinetics are further resolved into three processes occurring simultaneously and in series: a surface process, diffusion and phase transformation. The problem of determining the rate-limiting intrinsic process from the time-temperature-pressure ( t  T  P ) dependences of the different processes is discussed. The employment of surface modification techniques to complement the t  T  P analysis is emphasized. Most kinetics analyses that have identified an intrinsic process as rate limiting are criticized as being invalid because 1. (1) the rate theory used has been inappropriate. 2. (2) heat flow has not been adequately taken into account. The viewpoint adopted is that only nucleation and growth (NG) theory is applicable. The NG formalism is developed and is employed to treat the interplay between the simultaneous intrinsic processes which is generally ignored. NG theory is also employed to model kinetics behavior in order to discuss heat flow. The control of heat flow by the previously overlooked, but very useful, control of heat capacity is discussed.

185 citations

Journal ArticleDOI
Abstract: Rare‐earth transition metal compounds are known to be able to (reversibly) absorb large quantities of hydrogen gas at moderate pressures. This absorption of H2 gas leads to substantial changes of the magnetic properties. These include hydrogen induced transitions from Pauli paramagnetism to ferromagnetism. Examples also exist of the reverse effect, i.e., where in ferromagnetic compounds the 3d moment disappears upon hydrogen absorption. The changes in magnetic properties, together with experimental results of X‐ray diffraction and Mossbauer‐effect spectroscopy are discussed in terms of charge transfer and changes in interatomic distances. The metastable character of the ternary hydrides often leads to a loss of the long range atomic order upon hydrogen absorption. This affects not only the absorption capacity (after repeated cycling) but also influences the magnetic behavior. Examples are shown where the atomic disorder has led to pronounced thermomagnetic history effects.

81 citations

Journal ArticleDOI
TL;DR: In this article, the Moessbauer effect has been used to study hydrogen absorption in Dy, DyNi/sub 2, DyCo, DyMn, DyFe, and DyCo.
Abstract: The Moessbauer effect has been used to study hydrogen absorption in Dy, DyNi/sub 2/, DyCo/sub 2/, DyMn/sub 2/, and DyFe/sub 2/. Isomer shifts in the hydrides of the intermetallics are similar to those found in the dysprosium hydrides. Measurements at 4.2 /sup 0/K for the hydrides of the intermetallics show the magnetic order to be quite different from that of dysprosium hydride. Both atomically ordered and amorphous hydrides were studied.

76 citations

Journal ArticleDOI
G. Adachi1, H. Sakaguchi1, K. Niki1, N. Nagai1, J. Shimokawa1 
TL;DR: In this paper, the electrical resistivities of thin films of LaNi 5 were measured in a hydrogen atmosphere and the effect of the film thickness on the electrical properties during the hydrogen absorption-desorption process was also studied.
Abstract: Thin films of LaNi 5 were prepared by means of flash evaporation-deposition. The electrical resistivity of the films was measured in a hydrogen atmosphere. The films formed on the quartz substrates were amorphous. The resistivities of the films first increased and then decreased during the absorption of hydrogen. The reverse phenomenon was observed during the desorption process. The effect of the film thickness on the electrical properties during the hydrogen absorption-desorption process was also studied. Sample pulverization could be avoided by using a film less than 10 μm thick. The hydrogen content in the film was determined using the quartz crystal mass monitoring method.

38 citations

Journal ArticleDOI
TL;DR: In this paper, the C-15-type Laves phase structure of intermetallic compounds Zr 1-x Ho x Co 2 (x = 0.4, 0.6 and 0.8) was determined for the intermetall compounds with a temperature range 50-200 °C at pressures up to 40 bar.

36 citations