Hydrogen diffusion in the Laves-phase compound TiCr1.78

Mazzolai, Giovanni; Coluzzi, B.; Biscarini, A.; Mazzolai, F.M.; Tuissi, A.; Agresti, F.; Prìncìpí, G.; Russo, S. Lo

doi:10.1016/j.msea.2008.09.108

Cited by 3 publications

(4 citation statements)

References 13 publications

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“…The overall data concerning the H diffusion coefficient in the TiCrMn alloy system are collected in fig. 6, where the low temperature points are deduced from our own internal friction measurements with the binary alloy TiCr 1.78 [15]. In the same figure are also shown earlier QENS measurements of the tracer diffusion coefficient in the cubic (C15) TiCr 1.85 compound [13].…”

supporting

confidence: 65%

“…Quasi elastic neutron scattering [13] and NMR [14] techniques have been employed to investigate jump frequencies in the C15 form of the alloy TiCr 1.85 and diffusion data have been obtained in a limited range (313K-442K ) above room temperature. In order to characterize H mobility in the binary compound TiCr 1.78 over a much wider temperature range, H absorption and internal friction techniques have recently been applied and non-exponential behaviour has been observed [15].…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of Hydrogen in the Hexagonal (C14) Laves Phase Compounds TiCr1.8-xMnx

Mazzolai

2009

DDF

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The diffusion of hydrogen has been investigated in the AB2 Laves phase Compounds TiCr1.78 and TiCr1.4Mn0.4, by absorption techniques. It has been found that H at temperatures higher than 700 K diffuses through the classical over-barrier mechanism, while at low temperature (around 100 K) the diffusion is governed by phonon-assisted tunnelling. The activation energy for classical hopping is rather high and increases with the substitution of Mn for Cr. In the range of H contents nH investigated (nH=H/Me0.03) the chemical diffusion coefficient does not depend on the H concentration.

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supporting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Dynamics of Hydrogen in the Hexagonal (C14) Laves Phase Compounds TiCr1.8-xMnx

Mazzolai

2009

DDF

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“…This disconnect is particularly evident for vibrational properties. The presence of soft phonon modes in intermetallics has been identified as an essential contributor to thermoelectric performance, − superconductivity, − unusual magnetic phenomena, , magnetostriction, , hydrogen diffusion, , and structural phase transitions. − However, few methods exist for directly tying the presence of these phonon modes (represented in k-space, using the same irreducible representations of the crystal symmetry as the electronic wave functions) to specific geometrical arrangements of atoms. In this Article, we will demonstrate how such relationships between structure and vibrational properties can be quickly and vividly derived using Density Functional Theory-Chemical Pressure (DFT-CP) analysis.…”

Section: Introductionmentioning

confidence: 99%

Chemical Pressure Schemes for the Prediction of Soft Phonon Modes: A Chemist’s Guide to the Vibrations of Solid State Materials

Engelkemier

Fredrickson

2016

Chem. Mater.

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The vibrational modes of inorganic materials play a central role in determining their properties, as is illustrated by the importance of phonon–electron coupling in superconductivity, phonon scattering in thermoelectric materials, and soft phonon modes in structural phase transitions. However, the prediction and control of these vibrations requires an understanding of how crystal structure and the stiffness of interatomic interactions are related. For compounds whose relationships between bonding and structure remain unclear, the elucidation of such structure–property relationships is immensely challenging. In this Article, we demonstrate how the Chemical Pressure (CP) approach can be used to draw visual and intuitive schemes relating the structure and vibrational properties of a solid state compound using the output of DFT calculations. We begin by illustrating how phonon band structures can validate the DFT-CP approach. For some intermetallic crystal structures, such as the Laves phases, the details of the packing geometries make the resulting CP scheme very sensitive to assumptions about how space should be partitioned among the interatomic contacts. Using the Laves phase CaPd2 (MgCu2 type) as a model system, we demonstrate how the phonon band structure provides a reference against which the space-partitioning method can be refined. A key parameter we identify is the ionicity of the crystal structure: the assumption of some electron transfer from the Ca to the Pd leads to a close agreement between the CP distribution and the major features of its phonon band structure. In particular, atomic motions along directions of positive CP (indicative of overly short interatomic distances) contribute to high frequency modes, while those along negative CPs (corresponding to overly long distances) make up the lowest frequency modes. Finally, we apply this approach to Nb3Ge (Cr3Si type) and CaPd5 (CaCu5 type), for which low-frequency phonon modes correlate with superconductivity and a rich variety of superstructures, respectively. Through these examples, CP analysis will emerge as a means of predicting the presence of soft phonon modes in a crystal structure and a guide to how elemental substitutions will affect the frequencies of these modes.

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“…TiCr 2 crystallizes in three Laves phases, namely C14, C36 and C15, exhibiting large interstitial sites to accommodate guest molecules, like H 2 . TiCr 2 based alloys can be applied to sustainable energy applications for reversible H 2 storage [4][5][6], each Laves phases being able to absorb similar amount of H 2 [7]. H 2 absorption mechanism is a multistep process, involving adsorption on metal surface by molecular H 2 , its split into single atomic species, followed by diffusion of atomic hydrogen into the alloy forming a hydrade [8].…”

Section: Introductionmentioning

confidence: 99%