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25 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on UFeC2 by Materials Project

UFeC2 is Bixbyite (Mn,Fe)2O4-like structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. U6+ is bonded in a 4-coordinate geometry to eight equivalent C4- atoms. There are four shorter (2.39 Å) and four longer (2.86 Å) U–C bond lengths. Fe2+ is bonded to four equivalent C4- atoms to form distorted corner-sharing FeC4 trigonal pyramids. All Fe–C bond lengths are 1.87 Å. C4- is bonded in a 4-coordinate geometry to four equivalent U6+ and two equivalent Fe2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce4Se3O4 by Materials Project

Ce4Se3O4 is Bixbyite (Mn,Fe)2O4-like structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are four inequivalent Ce+3.50+ sites. In the first Ce+3.50+ site, Ce+3.50+ is bonded in a 4-coordinate geometry to four Se2- and four O2- atoms. There are two shorter (3.08 Å) and two longer (3.23 Å) Ce–Se bond lengths. There are a spread of Ce–O bond distances ranging from 2.34–2.42 Å. In the second Ce+3.50+ site, Ce+3.50+ is bonded in a 4-coordinate geometry to four Se2- and four O2- atoms. All Ce–Se bond lengths are 3.08 Å. There are two shorter (2.39 Å) and two longer (2.40 Å) Ce–O bond lengths. In the third Ce+3.50+ site, Ce+3.50+ is bonded in a 6-coordinate geometry to two equivalent Se2- and four O2- atoms. Both Ce–Se bond lengths are 3.12 Å. There are a spread of Ce–O bond distances ranging from 2.28–2.42 Å. In the fourth Ce+3.50+ site, Ce+3.50+ is bonded in a 4-coordinate geometry to four Se2- and four O2- atoms. There are two shorter (3.08 Å) and two longer (3.23 Å) Ce–Se bond lengths. There are a spread of Ce–O bond distances ranging from 2.34–2.43 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 4-coordinate geometry to four Ce+3.50+ atoms. In the second Se2- site, Se2- is bonded in a 4-coordinate geometry to four Ce+3.50+ atoms. In the third Se2- site, Se2- is bonded in a 6-coordinate geometry to six Ce+3.50+ atoms. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to four Ce+3.50+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the second O2- site, O2- is bonded to four Ce+3.50+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the third O2- site, O2- is bonded to four Ce+3.50+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the fourth O2- site, O2- is bonded to four Ce+3.50+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs2BaO2 by Materials Project

Cs2BaO2 is Bixbyite (Mn,Fe)2O4-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Cs1+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. There are a spread of Cs–O bond distances ranging from 2.94–3.46 Å. Ba2+ is bonded in a distorted rectangular see-saw-like geometry to four equivalent O2- atoms. There are two shorter (2.58 Å) and two longer (2.63 Å) Ba–O bond lengths. O2- is bonded in a 6-coordinate geometry to four equivalent Cs1+ and two equivalent Ba2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce2Cd(SeO)2 by Materials Project

Ce2Cd(SeO)2 is Bixbyite (Mn,Fe)2O4-derived structured and crystallizes in the tetragonal P4_2/nmc space group. The structure is three-dimensional. there are three inequivalent Ce3+ sites. In the first Ce3+ site, Ce3+ is bonded in a 4-coordinate geometry to four equivalent Se2- and four equivalent O2- atoms. All Ce–Se bond lengths are 3.27 Å. There are two shorter (2.34 Å) and two longer (2.35 Å) Ce–O bond lengths. In the second Ce3+ site, Ce3+ is bonded in a 4-coordinate geometry to four equivalent Se2- and four equivalent O2- atoms. All Ce–Se bond lengths are 3.27 Å. There are two shorter (2.34 Å) and two longer (2.35 Å) Ce–O bond lengths. In the third Ce3+ site, Ce3+ is bonded in a 4-coordinate geometry to four equivalent Se2- and four equivalent O2- atoms. All Ce–Se bond lengths are 3.27 Å. There are two shorter (2.34 Å) and two longer (2.35 Å) Ce–O bond lengths. Cd2+ is bonded to four equivalent Se2- atoms to form distorted corner-sharing CdSe4 tetrahedra. All Cd–Se bond lengths are 2.71 Å. Se2- is bonded in a 2-coordinate geometry to four equivalent Ce3+ and two equivalent Cd2+ atoms. O2- is bonded to four Ce3+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Gas-mediated trace element incorporation into rhyolite-hosted topaz: A synchrotron microbeam XAS study

Magmatic gas exsolving during late-stage cooling of shallow magmas has been considered an important facilitator of low-pressure alteration and metal transport. However, the chemical properties of such gas, particularly its metal transport mechanisms and capacity, remain elusive. Trace elements in minerals produced by gas-mediated surface reaction or precipitation from gas capture details of gas composition and reaction pathways. However, interpretation of mineral trace element contents is dependent on understanding crystallographic controls on gas/mineral partitioning. Here, this work investigates the structural accommodation of As, Mn, Ga, Ge, Fe, and Ti in vapor-deposited topaz of vesicular topaz rhyolite from the Thomas Range, Utah, through single-crystal synchrotron microbeam X-ray techniques on picogram quantities of those trace elements. X-ray absorption near edge structure (XANES) data indicates that these elements are incorporated into topaz as As 5+ , Fe 3+ , Mn 3+ , Ti 4+ , Ga 3+ , and Ge 4+ . Extended X-ray absorption fine structure (EXAFS) analysis for these trace elements, compared to EXAFS of structural Al and Si, reveals that As 5+ and Ge 4+ are incorporated directly into the tetrahedral site of the topaz structure, with the octahedral site accommodating Mn 3+ , Fe 3+ , Ga 3+ , and Ti 4+ . For As 5+ and Fe 3+ , the structural impact of substitution extends to at least second neighbors (other elements were only resolvable to first neighbors). Further interpretation of the EXAFS results suggests that the substitution of Ti 4+ results in increased distortion of the octahedral site, while the other trace elements induce more uniform expansion correlating in magnitude to their ionic radius. Comparison of quantified X-ray fluorescence (XRF) data for two topaz crystals from this rhyolite reveals variable trace element concentrations for As 5+ , Fe 3+ , Ga 3+ , and Ti 4+ , reflective of a source gas undersaturated in these trace elements changing in concentration over the period of topaz deposition. The identical Ge 4+ content of the two topaz crystals suggests that Ge 4+ in the gas was buffered by the growth of another Ge 4+ -bearing phase, such as quartz. The very low Mn 3+ content in the topaz crystals does not reflect the abundance of Mn 3+ in the gas (saturation of Mn is evidenced by coexisting bixbyite). Instead, it suggests a strong Jahn-Teller inhibitory effect to the substitution of Mn 3+ for Al 3+ in the distorted octahedral site of topaz. It is proposed that exsolution of an HF-enriched gas from cooling rhyolitic magma led to local scouring of Al, Si, and trace metals from the magma. Once topaz crystals nucleated, self-catalyzed reactions that recycle HF led to continued growth of topaz.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Thermal Analysis of High Entropy Rare Earth Oxides

Phase transformations in multicomponent rare earth sesquioxides were studied by splat quenching from the melt, high temperature differential thermal analysis and synchrotron X-ray diffraction on laser-heated samples. Three compositions were prepared by the solution combustion method: (La,Sm,Dy,Er,RE) 2 O 3 , where all oxides are in equimolar ratios and RE is Nd or Gd or Y. After annealing at 800 °C, all powders contained mainly a phase of C-type bixbyite structure. After laser melting, all samples were quenched in a single-phase monoclinic B-type structure. Thermal analysis indicated three reversible phase transitions in the range 1900–2400 °C, assigned as transformations into A, H, and X rare earth sesquioxides structure types. Unit cell volumes and volume changes on C-B, B-A, and H-X transformations were measured by X-ray diffraction and consistent with the trend in pure rare earth sesquioxides. The formation of single-phase solid solutions was predicted by Calphad calculations. The melting point was determined for the (La,Sm,Dy,Er,Nd) 2 O 3 sample as 2456 ± 12 °C, which is higher than for any of constituent oxides. An increase in melting temperature is probably related to nonideal mixing in the solid and/or the melt and prompts future investigation of the liquidus surface in Sm 2 O 3 -Dy 2 O 3 , Sm 2 O 3 -Er 2 O 3 , and Dy 2 O 3 -Er 2 O 3 systems.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Advances in Molecular Beam Epitaxy Growth of Ultra-Wide Bandgap Ga2O3 Based Alloys

Gallium oxide (Ga2O3) is an emerging ultra-wide bandgap semiconductor material that has attracted attention for its potential to outperform existing SiC and GaN based devices operating at high breakdown voltages and high temperature. Isovalent alloying of In and Al in Ga2O3 provides the ability to engineer bandgap energy and strain of the material. Alloying with Al increases the bandgap energy and the theoretically achievable Baliga's figure of merit, a key measure of a material's ultimate performance limits for high power switching devices. Alloying with In introduces compressive strain and can be used to counteract the tensile strain of Al incorporation. The resulting (AlxGa1-x-yIny)2O3 alloy can be lattice-matched to commercially available Ga2O3 wafers and has a tunable bandgap energy greater than that of Ga2O3, 4.76 eV. Such lattice-matched material can be grown arbitrarily thick without the detrimental effects of elastic strain and relaxation, making it suitable for high voltage diodes and transistors. However, efforts to synthesize isovalent alloys are complicated by their tendency to phase separate into corundum Al2O3 or bixbyite In2O3. Literature reports of the quaternary (AlxGa1-x-yIny)2O3 are limited to <1% unintentional indium incorporation in In-catalyzed (AlxGa1-x)2O3. The primary limitation to quaternary growth is the limited incorporation of indium at elevated growth temperatures. This limited incorporation is due to both the volatility of indium oxide and Al and Ga cation exchange reactions which replace indium in In2O3. We report on the development of a novel high-throughput molecular beam epitaxy (MBE) technique to screen the growth conditions for the ternary alloy (InyGa1-y)2O3, and the application of these findings to the first successful synthesis of phase pure monoclinic (AlxGa1-x-yIny)2O3 by MBE. By leveraging the unique sub-oxide chemistry of Ga2O3 and in-situ monitoring of crystal properties by reflection high-energy electron diffraction (RHEED), a cyclical growth and etch-back method is developed and applied to rapidly characterize the (InyGa1-y)2O3 growth space. This cyclical method provides approximately 10x increase in experimental throughput and up to 46x improvement in Ga2O3 substrate utilization. Appropriate growth conditions for monoclinic (InyGa1- y)2O3 are identified by machine learning analysis of RHEED patterns and targeted growths are characterized ex-situ to confirm improved In incorporation. These growth conditions are then combined with established (AlxGa1-x)2O3 growth conditions to grow quaternary (AlxGa1-x-yIny)2O3 with Al mole fractions ranging from 1.4% - 24.4% and In mole fractions ranging from 3.1% to 15.5%. The chemical and optical properties of the alloys are investigated by XRD, XPS, and spectroscopic ellipsometry. A lattice-matched (AlxGa1-x-yIny)2O3 alloy is examined by 4D-STEM and the chemical and physical uniformity of Al and In incorporation are discussed.

alloy↗