Deuterium site energy difference in ZrTi2D4.3 as studied by high-temperature neutron diffraction

Tokaychuk, Ya.; Keller, L.; Yvon, K.

doi:10.1016/j.jallcom.2004.11.018

Cited by 4 publications

(2 citation statements)

References 7 publications

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“…Only few other examples have been reported so far, such as the depopulation of Ho 6 interstices in the Ho 6 Fe 23 --H system [20], of La 4 Pd 2 interstices in the La 3 Pd 5 Si--H system [21], of ErCo 3 interstices in the ErCo 3 --H system [22], and of (Ti,Zr) 4 type interstices in the Ti 0:64 Zr 0:36 Ni--H system [23]. Partial H site depopulations are more common, such as those of Ce 2 (Mn,Al) 2 interstices in the CeMn 1:5 Al 0:5 --H [24] and CeMn 1:8 Al 0:2 H 4:4 --H systems [25], and of ErNi 3 interstices in the ErNi 3 --H system [26], or the temperature induced depopulation of AB 3 -type interstices at the benefit of A 2 B 2 -type interstices in the C15 type TiZr 2 --H system [27].…”

Section: Discussionmentioning

confidence: 99%

Hydrogen induced site depopulation in the LaMgNi₄-hydrogen system

Chotard¹,

Sheptyakov²,

Yvon³

2008

Zeitschrift Für Kristallographie

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Metal hydride structures / In-situ neutron powder diffraction / Pressure-composition-isotherms / Structure-property relation Abstract. The LaMgNi 4 -hydrogen system was investigated by in-situ neutron powder diffraction and pressurecomposition isotherm measurements at 100 C and hydrogen (deuterium) pressures of up 50 bar. The system displays three hydride phases that have distinctly different hydrogen plateau pressures and H atom distributions. The cubic a-LaMgNi 4 H 0:75 phase forms below 0.01 bar hydrogen pressure and H atoms fill one type of tetrahedral Ni 4 interstices. The orthorhombic distorted b-LaMgNiH 3:7 phase forms at $3 bar hydrogen pressure and H atoms fill both tetrahedral LaNi 3 and triangular bi-pyramidal La 2 MgNi 2 interstices. Interestingly, tetrahedral Ni 4 interstices are no longer occupied. Finally, the most hydrogen rich gLaMgNi 4 H 4:85 phase forms above 20 bar. It has again cubic symmetry and H atoms continue to occupy triangular bipyramidal La 2 MgNi 2 interstices while filling a new type of tetrahedral Ni 4 interstices that are neither occupied in the a-nor in the b-phase. The tetrahedral LaNi 3 interstices occupied in the b-phase are empty. Hydrogen induced depopulations of interstitial sites in metal hydrides are relatively rare and consistent with, but not entirely due to, the onset of repulsive H--H interactions at increasing hydrogen concentrations.

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Section: Discussionmentioning

confidence: 99%

Hydrogen induced site depopulation in the LaMgNi₄-hydrogen system

Chotard¹,

Sheptyakov²,

Yvon³

2008

Zeitschrift Für Kristallographie

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“…We saw none of the expected additional Cmmm superlattice peaks in the diffraction patterns of our powders that had rapidly cooled from high temperature. Further hydriding cycles revealed that a and u were completely replaced, principally by tetragonal ThH 2 structure-type and the l-Ti 2 ZrH 4 C15 Laves phase (MgCu 2 structure-type), together with free a-ZrO 2 , as observed in similar systems [43,44]. Upon dehydriding, the a-and uphases reappeared.…”

Section: X-ray and Neutron Diffractionmentioning

confidence: 71%

Omega-phase in Ti-Hf-Zr alloys produced by the hydride-cycle methodSpecial issue on Neutron Scattering in Canada.

et al. 2010

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Abstract:We report the presence of large proportions of u-phase in Ti-Hf-Zr alloys, prepared using the hydride cycle technique. We show that the u-phase extends across the concentration triangle of Ti-Zr-Hf and report the partitioning of the three metals across the two sites in this structure from neutron and X-ray data. We examine the symmetry of the order parameter governing the b-u phase transition and show that a two-step model for the phase transition involving site ordering followed by displacement is not likely to be correct. We suggest that an interstitial solid solution of oxygen and octahedral vacancies exists, and that the observation of any u-phase diffraction pattern of alloys of these metals at ambient temperature and pressure should be viewed as a potential sign of the presence of oxygen in the octahedral interstitial sites. Résumé : Dans cet article, nous rapportons la présence d'une importante proportion de la phase dite u dans les alliages Ti-Hf-Zr, préparés par une technique de cyclage sous hydrogène (hydride cycle). Nous montrons également que la phase u s'étend à travers le diagramme de concentration triangulaire de Ti-Hf-Zr. De plus, à partir de données de diffractions des neutrons, nous trouvons que les trois métaux se répartissent sur les deux sites distincts dans la structure. Nous examinons la symetrie du paramètre d'ordre qui gouverne la transition de phase b-u et nous montrons qu'un modèle à deux étages pour la transition de phase est improbable. Nous suggérons plutôt la présence d'une solution solide interstitielle d'oxygène et de lacunes octaédriques. De plus, si la phase u est observée dans le diagramme de diffraction d'alliages de ces métaux à température et pression ambiente, on doit la considérer comme un signe possible de la présence d'oxygène sur les sites interstitiels octaédriques.

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