The structure of the λ-phase of niobium-deuterium

Brun, T. O.; Kajitani, T.; Müller, Melanie; Westlake, D.G.; Makenas, Bruce J.; Birnbaum, H.K.

doi:10.1063/1.31811

Cited by 3 publications

(15 citation statements)

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“…A Rietveld analysis has been performed using the β phase structure model since the peaks dominated by the scattering contribution of the niobium atoms allow one to determine the lattice constants (table 8). Many peaks affected by a hydrogen contribution are split into satellite peaks, which is in accordance with observations by Brun et al [7].…”

Section: Diagrams Measured Below 200 K: λ Phasessupporting

confidence: 92%

“…In many references they are commonly denoted as λ phases or λ phase regions as will be done below. However, neutron scattering [7] and TEM results [5,8] are at variance with these results of Köbler and Welter. Makenas and Birnbaum [5] also denied the existence of the γ phase proposed by Pick for x ≈ 0.9 [9].…”

Section: Introductionmentioning

confidence: 81%

“…the structure of the microdomain boundaries and the existence of incommensurate modulated phases. Furthermore, the model is not confirmed yet, although Welter and Schöndube [10] detected superstructure reflections in neutron diffractograms of NbD 0.825 similar to those measured by Brun et al [7]. Hauck had proposed a structure model of the γ phase [11].…”

Section: Introductionmentioning

confidence: 90%

“…We examined the structure model proposed in [5,7] using the program POWLS in a first trial. We chose k z = 0. the existence of intrinsic deuterium vacancies within the microdomain boundaries.…”

Section: Diagrams Measured Below 200 K: λ Phasesmentioning

confidence: 99%

“…Makenas and Birnbaum [5] also denied the existence of the γ phase proposed by Pick for x ≈ 0.9 [9]. According to a structure model of the λ phases [5,7] sequences of two kinds of β phase microdomains alternate along the c direction. These two kinds of cells differ by a rotation of 180 • and build up a modulated structure (figure 2).…”

Section: Introductionmentioning

confidence: 99%

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Neutron scattering studies on the vibrational excitations and the structure of ordered niobium hydrides: the phases

Hauer¹,

Hempelmann²,

Udovic³

et al. 2004

J. Phys.: Condens. Matter

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Neutron vibrational spectroscopy and neutron diffraction have been used to study the optical hydrogen vibrations in and the structure of ordered niobium hydrides NbH x and deuterides NbD x in the concentration range 0.73 < x < 1.0 and at temperatures between 13 and 250 K. The measurements performed at temperatures above 200 K confirm the established model of the β phase. Neutron diffraction data collected in the regime of the λ phases (T < 200 K, 0.73 < x < 1.0) show that the structure for x < 0.85 is made up of microdomains with β phase structure. Neutron vibrational spectra display up to three families of peaks that can be assigned to three different hydrogen sites: an undisturbed tetrahedral site within the microdomains and two strongly disturbed tetrahedral sites within two different kinds of microdomain boundaries. Incommensurately modulated phases probably exist in this concentration range. For hydrogen concentrations around x ≈ 0.85 there is evidence for a change of symmetry of the basic cell as well as a change of the modulation at even higher concentrations. In the range of the γ phase at x ≈ 0.9, strong isotopic effects occur. The results give new insights into the phase diagram.

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Section: Diagrams Measured Below 200 K: λ Phasessupporting

confidence: 92%

Section: Introductionmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 90%

Section: Diagrams Measured Below 200 K: λ Phasesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Neutron scattering studies on the vibrational excitations and the structure of ordered niobium hydrides: the phases

Hauer¹,

Hempelmann²,

Udovic³

et al. 2004

J. Phys.: Condens. Matter

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Order-disorder phase transitions in

Plackowski

Сорокина

Wlosewicz

1998

J. Phys.: Condens. Matter

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Measurements of the electrical resistivity under hydrostatic pressure have been made and an x-ray analysis has been performed for the interstitial alloy NbH 0.86 . The results have been compared with specific heat and thermal expansion results for the same sample. An anomaly in the specific heat observed at 388-394 K was attributed to a phase transition due to the ordering of H atoms. The trapezoidal shape of the anomaly was explained in terms of the equilibrium phase separation occurring within the two-phase region, as in the case of the liquid-solutionvapour transition. At lower temperatures a series of specific heat anomalies at ∼194 K (small), ∼203 K (medium) and ∼216 K (large) was observed and assigned to the subsequent orderings of the H atoms. The smallest anomaly coincides with the change of the Nb-sublattice symmetry which is cubic below and orthorhombic above the temperature at which this anomaly is found and also, with a bend in the curve representing the temperature dependence of the resistivity. The temperature location of this bend has been found to be insensitive to the applied pressure (up to 19.5 kbar). The biggest low-temperature specific heat anomaly coincides with a jump in the relative elongation.

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