Powgen: A third-generation highresolution high-throughput powder diffraction instrument at the Spallation Neutron Source

Huq, Ashfia; Hodges, J. P.; Heroux, Luke; Gourdon, Olivier

doi:10.1524/9783486991321-024

Cited by 97 publications

(106 citation statements)

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“…Neutron diffraction experiments were performed at the ORNL Spallation Neutron Source (SNS) 65 using instruments optimized for studies of local structures (NOMAD, Nanoscale-ordered Materials Diffractometer) 40 and long-range crystal ordering (POWGEN) 66 . The use of both NOMAD and POWGEN was motivated by the expectation that the present HEAs have distinct local features (for example, lattice distortions and local ordering), as well as long-range crystal order.…”

Section: Methodsmentioning

confidence: 99%

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

et al. 2015

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The alloy-design strategy of combining multiple elements in near-equimolar ratios has shown great potential for producing exceptional engineering materials, often known as 'high-entropy alloys'. Understanding the elemental distribution, and, thus, the evolution of the configurational entropy during solidification, is undertaken in the present study using the Al 1.3 CoCrCuFeNi model alloy. Here we show that, even when the material undergoes elemental segregation, precipitation, chemical ordering and spinodal decomposition, a significant amount of disorder remains, due to the distributions of multiple elements in the major phases. The results suggest that the high-entropy alloy-design strategy may be applied to a wide range of complex materials, and should not be limited to the goal of creating single-phase solid solutions.

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Section: Methodsmentioning

confidence: 99%

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

et al. 2015

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“…Neutron time-of-flight powder diffraction measurements were carried out using the POWGEN diffractometer at the Spallation Neutron Source [37] using the same powder sample described in Sec. II B, with the sample encased in a thin-walled vanadium can.…”

Section: Inelastic X-ray Scatteringmentioning

confidence: 99%

Lattice dynamics and thermal transport in multiferroicCuCrO2

et al. 2017

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Inelastic neutron and x-ray scattering measurements of phonons and spin waves were performed in the delafossite compound CuCrO2 over a wide range of temperature, and complemented with first-principles lattice dynamics simulations. The phonon dispersions and density of states are well reproduced by our density functional calculations, and reveal a strong anisotropy of Cu vibrations, which exhibit low-frequency modes of large amplitude parallel to the basal plane of the layered delafossite structure. The low frequency in-plane modes also show a systematic temperature dependence of neutron and x-ray scattering intensities. In addition, we find that spin fluctuations persist above 300 K, far above the Néel temperature for long-range antiferromagnetic order, T N ≃ 24 K. Our modeling of the thermal conductivity, based on our phonon measurements and simulations, reveals a significant anisotropy and indicates that spin fluctuations above T N constitute an important source of phonon scattering, considerably suppressing the thermal conductivity compared to that of the isostructural but non-magnetic compound CuAlO2.

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“…A vanadium standard was measured to correct the efficiency of the raw detector counts. 21 Rietveld refinements were carried out using the GSAS software package and the EXPGUI interface 22,23 with d-spacings from ∼0.5 to 3.0Å.…”

Section: B Crystal Structures and Phase Puritymentioning

confidence: 99%

Thermoelectric transport properties of CaMg2Bi2, EuMg2Bi
May
¹
,
McGuire
²
,
Singh
³

et al. 2012
Phys. Rev. B

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The thermoelectric transport properties of CaMg2Bi2, EuMg2Bi2, and YbMg2Bi2 were characterized between 2 and 650 K. As synthesized, the polycrystalline samples are found to have lower p-type carrier concentrations than single-crystalline samples of the same empirical formula. These low carrier concentration samples possess the highest mobilities yet reported for materials with the CaAl2Si2 structure type, with a mobility of ∼740 cm 2 /V/s observed in EuMg2Bi2 at 50 K. Despite decreases in the Seebeck coefficient (α) and electrical resistivity (ρ) with increasing temperature, the power factor (α 2 /ρ) increases for all temperatures examined. This behavior suggests a strong asymmetry in the conduction of electrons and holes. The highest figure of merit (zT ) is observed in YbMg2Bi2, with zT approaching 0.4 at 600 K for two samples with carrier densities of approximately 2×1018 cm −3 and 8×10 18 cm −3 at room temperature. Refinements of neutron powder diffraction data yield similar behavior for the structures of CaMg2Bi2 and YbMg2Bi2, with smooth lattice expansion and relative expansion in c being ∼35% larger than relative expansion in a at 973 K. First principles calculations reveal an increasing band gap as Bi is replaced by Sb then As, and subsequent Boltzmann transport calculations predict an increase in α for a given n associated with an increased effective mass as the gap opens. The magnitude and temperature dependence of α suggests higher zT is likely to be achieved at larger carrier concentrations, roughly an order of magnitude higher than those in the current polycrystalline samples, which is also expected from the detailed calculations.

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Powgen: A third-generation highresolution high-throughput powder diffraction instrument at the Spallation Neutron Source

Cited by 97 publications

References 0 publications

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

Lattice dynamics and thermal transport in multiferroicCuCrO2

Thermoelectric transport properties of CaMg2Bi2, EuMg2Bi
May
¹
,
McGuire
²
,
Singh
³

et al. 2012
Phys. Rev. B

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Powgen: A third-generation highresolution high-throughput powder diffraction instrument at the Spallation Neutron Source

Cited by 97 publications

References 0 publications

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

Lattice dynamics and thermal transport in multiferroicCuCrO2

Thermoelectric transport properties of CaMg2Bi2, EuMg2BiMay1, McGuire2, Singh3 et al. 2012Phys. Rev. B

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Thermoelectric transport properties of CaMg2Bi2, EuMg2Bi
May
¹
,
McGuire
²
,
Singh
³

et al. 2012
Phys. Rev. B