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Hassan M Helmy - One of the best experts on this subject based on the ideXlab platform.
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the behavior of pt pd cu and ni in the se Sulfide System between 1050 and 700 c and the role of se in platinum group elements fractionation in Sulfide melts
Geochimica et Cosmochimica Acta, 2017Co-Authors: Hassan M Helmy, Raul O C FonsecaAbstract:Abstract The behavior of Pt, Pd, Ni and Cu in Se-Sulfide System and the role of Se in platinum-group elements (PGE) fractionation have been experimentally investigated at temperatures between 1050 and 700 °C in evacuated silica tubes. At 1050 °C, Se partially partitions into a vapor phase. At 980 °C, monoSulfide solid solution (mss) and Sulfide melt are the only stable phases. No Pt or Pd-bearing discrete selenide phases form down to 700 °C. Instead cooperite (PtS) forms at 900 °C. Both mss and Sulfide melt can accommodate wt.% levels of Se over the whole temperature range covered by the experiments. The addition of Se in the Sulfide System leads to an increase in the activity coefficients of Ni and Pd in Sulfide melt. This is reflected by an increase in the partition coefficients of Ni and Pd between mss and Sulfide melt. The Pt-Se activity coefficient in Sulfide melt is lower than that of Pt-S. Owing to selenium’s high solubility in Sulfides, there never become oversaturated in Se to the extent that discrete selenides form. As such, base metal Sulfides are expected to control the geochemical behavior of Se in natural Systems. Interestingly, partition coefficients for the platinum-group elements (Os, Ir, Ru, Pt, Rh, Pd) between mss and Sulfide melt are undistinguishable regardless of whether Se is present or not. These results imply that Se plays little role in the fractionation of PGE as Sulfide melt cools down and crystallize. Furthermore, our experimental results provide evidence that Se is volatile at magmatic temperature and is likely to be degassed like sulfur.
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platinum group elements fractionation by selective complexing the os ir ru rh arsenide Sulfide Systems above 1020 c
Geochimica et Cosmochimica Acta, 2017Co-Authors: Hassan M Helmy, Alessandro BragagniAbstract:Abstract The platinum-group element (PGE) contents in magmatic ores and rocks are normally in the low μg/g (even in the ng/g) level, yet they form discrete platinum-group mineral (PGM) phases. IPGE (Os, Ir, Ru) + Rh form alloys, Sulfides, and sulfarsenides while Pt and Pd form arsenides, tellurides, bismuthoids and antimonides. We experimentally investigate the behavior of Os, Ru, Ir and Rh in As-bearing Sulfide System between 1300 and 1020 °C and show that the prominent mineralogical difference between IPGE (+Rh) and Pt and Pd reflects different chemical preference in the Sulfide melt. At temperatures above 1200 °C, Os shows a tendency to form alloys. Ruthenium forms a Sulfide (laurite RuS2) while Ir and Rh form sulfarsenides (irarsite IrAsS and hollingworthite RhAsS, respectively). The chemical preference of PGE is selective: IPGE + Rh form metal–metal, metal-S and metal-AsS complexes while Pt and Pd form semimetal complexes. Selective complexing followed by mechanical separation of IPGE (and Rh)-ligand from Pt- and Pd-ligand associations lead to PGE fractionation.
Ion Errea - One of the best experts on this subject based on the ideXlab platform.
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quantum crystal structure in the 250 kelvin superconducting lanthanum hydride
Nature, 2020Co-Authors: Ion Errea, Francesco Belli, Lorenzo Monacelli, A Sanna, Takashi Koretsune, Terumasa Tadano, Raffaello BiancoAbstract:The discovery of superconductivity at 200 kelvin in the hydrogen Sulfide System at high pressures1 demonstrated the potential of hydrogen-rich materials as high-temperature superconductors. Recent theoretical predictions of rare-earth hydrides with hydrogen cages2,3 and the subsequent synthesis of LaH10 with a superconducting critical temperature (Tc) of 250 kelvin4,5 have placed these materials on the verge of achieving the long-standing goal of room-temperature superconductivity. Electrical and X-ray diffraction measurements have revealed a weakly pressure-dependent Tc for LaH10 between 137 and 218 gigapascals in a structure that has a face-centred cubic arrangement of lanthanum atoms5. Here we show that quantum atomic fluctuations stabilize a highly symmetrical [Formula: see text] crystal structure over this pressure range. The structure is consistent with experimental findings and has a very large electron-phonon coupling constant of 3.5. Although ab initio classical calculations predict that this [Formula: see text] structure undergoes distortion at pressures below 230 gigapascals2,3, yielding a complex energy landscape, the inclusion of quantum effects suggests that it is the true ground-state structure. The agreement between the calculated and experimental Tc values further indicates that this phase is responsible for the superconductivity observed at 250 kelvin. The relevance of quantum fluctuations calls into question many of the crystal structure predictions that have been made for hydrides within a classical approach and that currently guide the experimental quest for room-temperature superconductivity6-8. Furthermore, we find that quantum effects are crucial for the stabilization of solids with high electron-phonon coupling constants that could otherwise be destabilized by the large electron-phonon interaction9, thus reducing the pressures required for their synthesis.
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quantum hydrogen bond symmetrization in the superconducting hydrogen Sulfide System
Nature, 2016Co-Authors: Ion Errea, Hanyu Liu, Matteo Calandra, Richard J. Needs, Francesco Mauri, Yunwei Zhang, Chris J. Pickard, Joseph R NelsoAbstract:Ab initio calculations are used to determine the contribution of quantum fluctuations to the crystal structure of the high-pressure superconducting phase of H3S and D3S; the quantum nature of the proton is found to fundamentally change the superconducting phase diagram of H3S. The discovery of high-temperature superconductivity in the pressurized hydrogen Sulfide System has triggered a flurry of activity from researchers in the field eager to characterize the superconducting phase. Ion Errea et al. bring ab initio calculations to bear on the problem, and are able to pinpoint the contribution of quantum proton fluctuations in determining the crystal structure of the high-pressure superconducting phase of H3S and D3S. The quantum nature of the proton is found to fundamentally change the superconducting phase diagram of H3S. This process is analogous to the hydrogen-bond symmetrization known to occur in water under pressure. The quantum nature of the proton can crucially affect the structural and physical properties of hydrogen compounds. For example, in the high-pressure phases1,2 of H2O, quantum proton fluctuations lead to symmetrization of the hydrogen bond and reduce the boundary between asymmetric and symmetric structures in the phase diagram by 30 gigapascals (ref. 3). Here we show that an analogous quantum symmetrization occurs in the recently discovered4 sulfur hydride superconductor with a superconducting transition temperature Tc of 203 kelvin at 155 gigapascals—the highest Tc reported for any superconductor so far. Superconductivity occurs via the formation of a compound with chemical formula H3S (sulfur trihydride) with sulfur atoms arranged on a body-centred cubic lattice5,6,7,8,9. If the hydrogen atoms are treated as classical particles, then for pressures greater than about 175 gigapascals they are predicted to sit exactly halfway between two sulfur atoms in a structure with symmetry. At lower pressures, the hydrogen atoms move to an off-centre position, forming a short H–S covalent bond and a longer H···S hydrogen bond in a structure with R3m symmetry5,6,7,8,9. X-ray diffraction experiments confirm the H3S stoichiometry and the sulfur lattice sites, but were unable to discriminate between the two phases10. Ab initio density-functional-theory calculations show that quantum nuclear motion lowers the symmetrization pressure by 72 gigapascals for H3S and by 60 gigapascals for D3S. Consequently, we predict that the phase dominates the pressure range within which the high Tc was measured. The observed pressure dependence of Tc is accurately reproduced in our calculations for the phase, but not for the R3m phase. Therefore, the quantum nature of the proton fundamentally changes the superconducting phase diagram of H3S.
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Quantum hydrogen-bond symmetrization in the superconducting hydrogen Sulfide System
Nature, 2016Co-Authors: Ion Errea, Hanyu Liu, Matteo Calandra, Richard J. Needs, Yanming Ma, Joseph R Nelson, Yinwei Li, Yunwei Zhang, Chris J. Pickard, Francesco MauriAbstract:The quantum nature of the proton can crucially affect the structural and physical properties of hydrogen compounds. For example, in the high-pressure phases of H2O, quantum proton fluctuations lead to symmetrization of the hydrogen bond and reduce the boundary between asymmetric and symmetric structures in the phase diagram by 30 gigapascals (ref. 3). Here we show that an analogous quantum symmetrization occurs in the recently discovered sulfur hydride superconductor with a superconducting transition temperature Tc of 203 kelvin at 155 gigapascals-the highest Tc reported for any superconductor so far. Superconductivity occurs via the formation of a compound with chemical formula H3S (sulfur trihydride) with sulfur atoms arranged on a body-centred cubic lattice. If the hydrogen atoms are treated as classical particles, then for pressures greater than about 175 gigapascals they are predicted to sit exactly halfway between two sulfur atoms in a structure with symmetry. At lower pressures, the hydrogen atoms move to an off-centre position, forming a short H-S covalent bond and a longer H···S hydrogen bond in a structure with R3m symmetry. X-ray diffraction experiments confirm the H3S stoichiometry and the sulfur lattice sites, but were unable to discriminate between the two phases. Ab initio density-functional-theory calculations show that quantum nuclear motion lowers the symmetrization pressure by 72 gigapascals for H3S and by 60 gigapascals for D3S. Consequently, we predict that the phase dominates the pressure range within which the high Tc was measured. The observed pressure dependence of Tc is accurately reproduced in our calculations for the phase, but not for the R3m phase. Therefore, the quantum nature of the proton fundamentally changes the superconducting phase diagram of H3S.
Francesco Mauri - One of the best experts on this subject based on the ideXlab platform.
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quantum hydrogen bond symmetrization in the superconducting hydrogen Sulfide System
Nature, 2016Co-Authors: Ion Errea, Hanyu Liu, Matteo Calandra, Richard J. Needs, Francesco Mauri, Yunwei Zhang, Chris J. Pickard, Joseph R NelsoAbstract:Ab initio calculations are used to determine the contribution of quantum fluctuations to the crystal structure of the high-pressure superconducting phase of H3S and D3S; the quantum nature of the proton is found to fundamentally change the superconducting phase diagram of H3S. The discovery of high-temperature superconductivity in the pressurized hydrogen Sulfide System has triggered a flurry of activity from researchers in the field eager to characterize the superconducting phase. Ion Errea et al. bring ab initio calculations to bear on the problem, and are able to pinpoint the contribution of quantum proton fluctuations in determining the crystal structure of the high-pressure superconducting phase of H3S and D3S. The quantum nature of the proton is found to fundamentally change the superconducting phase diagram of H3S. This process is analogous to the hydrogen-bond symmetrization known to occur in water under pressure. The quantum nature of the proton can crucially affect the structural and physical properties of hydrogen compounds. For example, in the high-pressure phases1,2 of H2O, quantum proton fluctuations lead to symmetrization of the hydrogen bond and reduce the boundary between asymmetric and symmetric structures in the phase diagram by 30 gigapascals (ref. 3). Here we show that an analogous quantum symmetrization occurs in the recently discovered4 sulfur hydride superconductor with a superconducting transition temperature Tc of 203 kelvin at 155 gigapascals—the highest Tc reported for any superconductor so far. Superconductivity occurs via the formation of a compound with chemical formula H3S (sulfur trihydride) with sulfur atoms arranged on a body-centred cubic lattice5,6,7,8,9. If the hydrogen atoms are treated as classical particles, then for pressures greater than about 175 gigapascals they are predicted to sit exactly halfway between two sulfur atoms in a structure with symmetry. At lower pressures, the hydrogen atoms move to an off-centre position, forming a short H–S covalent bond and a longer H···S hydrogen bond in a structure with R3m symmetry5,6,7,8,9. X-ray diffraction experiments confirm the H3S stoichiometry and the sulfur lattice sites, but were unable to discriminate between the two phases10. Ab initio density-functional-theory calculations show that quantum nuclear motion lowers the symmetrization pressure by 72 gigapascals for H3S and by 60 gigapascals for D3S. Consequently, we predict that the phase dominates the pressure range within which the high Tc was measured. The observed pressure dependence of Tc is accurately reproduced in our calculations for the phase, but not for the R3m phase. Therefore, the quantum nature of the proton fundamentally changes the superconducting phase diagram of H3S.
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Quantum hydrogen-bond symmetrization in the superconducting hydrogen Sulfide System
Nature, 2016Co-Authors: Ion Errea, Hanyu Liu, Matteo Calandra, Richard J. Needs, Yanming Ma, Joseph R Nelson, Yinwei Li, Yunwei Zhang, Chris J. Pickard, Francesco MauriAbstract:The quantum nature of the proton can crucially affect the structural and physical properties of hydrogen compounds. For example, in the high-pressure phases of H2O, quantum proton fluctuations lead to symmetrization of the hydrogen bond and reduce the boundary between asymmetric and symmetric structures in the phase diagram by 30 gigapascals (ref. 3). Here we show that an analogous quantum symmetrization occurs in the recently discovered sulfur hydride superconductor with a superconducting transition temperature Tc of 203 kelvin at 155 gigapascals-the highest Tc reported for any superconductor so far. Superconductivity occurs via the formation of a compound with chemical formula H3S (sulfur trihydride) with sulfur atoms arranged on a body-centred cubic lattice. If the hydrogen atoms are treated as classical particles, then for pressures greater than about 175 gigapascals they are predicted to sit exactly halfway between two sulfur atoms in a structure with symmetry. At lower pressures, the hydrogen atoms move to an off-centre position, forming a short H-S covalent bond and a longer H···S hydrogen bond in a structure with R3m symmetry. X-ray diffraction experiments confirm the H3S stoichiometry and the sulfur lattice sites, but were unable to discriminate between the two phases. Ab initio density-functional-theory calculations show that quantum nuclear motion lowers the symmetrization pressure by 72 gigapascals for H3S and by 60 gigapascals for D3S. Consequently, we predict that the phase dominates the pressure range within which the high Tc was measured. The observed pressure dependence of Tc is accurately reproduced in our calculations for the phase, but not for the R3m phase. Therefore, the quantum nature of the proton fundamentally changes the superconducting phase diagram of H3S.
Alessandro Bragagni - One of the best experts on this subject based on the ideXlab platform.
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platinum group elements fractionation by selective complexing the os ir ru rh arsenide Sulfide Systems above 1020 c
Geochimica et Cosmochimica Acta, 2017Co-Authors: Hassan M Helmy, Alessandro BragagniAbstract:Abstract The platinum-group element (PGE) contents in magmatic ores and rocks are normally in the low μg/g (even in the ng/g) level, yet they form discrete platinum-group mineral (PGM) phases. IPGE (Os, Ir, Ru) + Rh form alloys, Sulfides, and sulfarsenides while Pt and Pd form arsenides, tellurides, bismuthoids and antimonides. We experimentally investigate the behavior of Os, Ru, Ir and Rh in As-bearing Sulfide System between 1300 and 1020 °C and show that the prominent mineralogical difference between IPGE (+Rh) and Pt and Pd reflects different chemical preference in the Sulfide melt. At temperatures above 1200 °C, Os shows a tendency to form alloys. Ruthenium forms a Sulfide (laurite RuS2) while Ir and Rh form sulfarsenides (irarsite IrAsS and hollingworthite RhAsS, respectively). The chemical preference of PGE is selective: IPGE + Rh form metal–metal, metal-S and metal-AsS complexes while Pt and Pd form semimetal complexes. Selective complexing followed by mechanical separation of IPGE (and Rh)-ligand from Pt- and Pd-ligand associations lead to PGE fractionation.
Yunwei Zhang - One of the best experts on this subject based on the ideXlab platform.
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quantum hydrogen bond symmetrization in the superconducting hydrogen Sulfide System
Nature, 2016Co-Authors: Ion Errea, Hanyu Liu, Matteo Calandra, Richard J. Needs, Francesco Mauri, Yunwei Zhang, Chris J. Pickard, Joseph R NelsoAbstract:Ab initio calculations are used to determine the contribution of quantum fluctuations to the crystal structure of the high-pressure superconducting phase of H3S and D3S; the quantum nature of the proton is found to fundamentally change the superconducting phase diagram of H3S. The discovery of high-temperature superconductivity in the pressurized hydrogen Sulfide System has triggered a flurry of activity from researchers in the field eager to characterize the superconducting phase. Ion Errea et al. bring ab initio calculations to bear on the problem, and are able to pinpoint the contribution of quantum proton fluctuations in determining the crystal structure of the high-pressure superconducting phase of H3S and D3S. The quantum nature of the proton is found to fundamentally change the superconducting phase diagram of H3S. This process is analogous to the hydrogen-bond symmetrization known to occur in water under pressure. The quantum nature of the proton can crucially affect the structural and physical properties of hydrogen compounds. For example, in the high-pressure phases1,2 of H2O, quantum proton fluctuations lead to symmetrization of the hydrogen bond and reduce the boundary between asymmetric and symmetric structures in the phase diagram by 30 gigapascals (ref. 3). Here we show that an analogous quantum symmetrization occurs in the recently discovered4 sulfur hydride superconductor with a superconducting transition temperature Tc of 203 kelvin at 155 gigapascals—the highest Tc reported for any superconductor so far. Superconductivity occurs via the formation of a compound with chemical formula H3S (sulfur trihydride) with sulfur atoms arranged on a body-centred cubic lattice5,6,7,8,9. If the hydrogen atoms are treated as classical particles, then for pressures greater than about 175 gigapascals they are predicted to sit exactly halfway between two sulfur atoms in a structure with symmetry. At lower pressures, the hydrogen atoms move to an off-centre position, forming a short H–S covalent bond and a longer H···S hydrogen bond in a structure with R3m symmetry5,6,7,8,9. X-ray diffraction experiments confirm the H3S stoichiometry and the sulfur lattice sites, but were unable to discriminate between the two phases10. Ab initio density-functional-theory calculations show that quantum nuclear motion lowers the symmetrization pressure by 72 gigapascals for H3S and by 60 gigapascals for D3S. Consequently, we predict that the phase dominates the pressure range within which the high Tc was measured. The observed pressure dependence of Tc is accurately reproduced in our calculations for the phase, but not for the R3m phase. Therefore, the quantum nature of the proton fundamentally changes the superconducting phase diagram of H3S.
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Quantum hydrogen-bond symmetrization in the superconducting hydrogen Sulfide System
Nature, 2016Co-Authors: Ion Errea, Hanyu Liu, Matteo Calandra, Richard J. Needs, Yanming Ma, Joseph R Nelson, Yinwei Li, Yunwei Zhang, Chris J. Pickard, Francesco MauriAbstract:The quantum nature of the proton can crucially affect the structural and physical properties of hydrogen compounds. For example, in the high-pressure phases of H2O, quantum proton fluctuations lead to symmetrization of the hydrogen bond and reduce the boundary between asymmetric and symmetric structures in the phase diagram by 30 gigapascals (ref. 3). Here we show that an analogous quantum symmetrization occurs in the recently discovered sulfur hydride superconductor with a superconducting transition temperature Tc of 203 kelvin at 155 gigapascals-the highest Tc reported for any superconductor so far. Superconductivity occurs via the formation of a compound with chemical formula H3S (sulfur trihydride) with sulfur atoms arranged on a body-centred cubic lattice. If the hydrogen atoms are treated as classical particles, then for pressures greater than about 175 gigapascals they are predicted to sit exactly halfway between two sulfur atoms in a structure with symmetry. At lower pressures, the hydrogen atoms move to an off-centre position, forming a short H-S covalent bond and a longer H···S hydrogen bond in a structure with R3m symmetry. X-ray diffraction experiments confirm the H3S stoichiometry and the sulfur lattice sites, but were unable to discriminate between the two phases. Ab initio density-functional-theory calculations show that quantum nuclear motion lowers the symmetrization pressure by 72 gigapascals for H3S and by 60 gigapascals for D3S. Consequently, we predict that the phase dominates the pressure range within which the high Tc was measured. The observed pressure dependence of Tc is accurately reproduced in our calculations for the phase, but not for the R3m phase. Therefore, the quantum nature of the proton fundamentally changes the superconducting phase diagram of H3S.
