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High-temperature superconductivity in compressed solid silane.

Zhang H, Jin X, Lv Y, Zhuang Q, Liu Y, Lv Q, Bao K, Li D, Liu B, Cui T - Sci Rep (2015)

Bottom Line: Crystal structures of silane have been extensively investigated using ab initio evolutionary simulation methods at high pressures.Two metallic structures with P2₁/c and C2/m symmetries are found stable above 383 GPa.Perturbative linear-response calculations for C2/m silane at 610 GPa reveal a high superconducting critical temperature that beyond the order of 10(2) K.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Superhard Materials, College of physics, Jilin University, Changchun, 130012, P. R. China.

ABSTRACT
Crystal structures of silane have been extensively investigated using ab initio evolutionary simulation methods at high pressures. Two metallic structures with P2₁/c and C2/m symmetries are found stable above 383 GPa. The superconductivities of metallic phases are fully explored under BCS theory, including the reported C2/c one. Perturbative linear-response calculations for C2/m silane at 610 GPa reveal a high superconducting critical temperature that beyond the order of 10(2) K.

No MeSH data available.


Enthalpy difference curves of Silane.Calculated enthalpies per SiH4 unit of various structures relative to our predicted Cmcm structure as a function of pressure range from 300–1000 GPa. Inset: Enthalpies in the pressure range from 310 GPa to 430 GPa.
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f1: Enthalpy difference curves of Silane.Calculated enthalpies per SiH4 unit of various structures relative to our predicted Cmcm structure as a function of pressure range from 300–1000 GPa. Inset: Enthalpies in the pressure range from 310 GPa to 430 GPa.

Mentions: The crystal structures of silane were predicted with one to six SiH4 formula units per cell. Several competitive candidates for energy with the space groups C2/c (2 molecules/cell), Cmcm (2 molecules/cell), I4/mmm (3 molecules/cell), P21/c (4 molecules/cell), P21/m (4 molecules/cell), P-1 (4 molecules/cell) and C2/m (6 molecules/cell) were obtained. The enthalpies of candidates are plotted as a function of pressures in Figure 1. Above the 300 GPa, there are two competitive enthalpy structures with the C2/c and P21/c symmetry. The maximum enthalpy difference between them is only 0.01 (eV/unit cell) over the pressure range from 300 GPa to 383 GPa, see Figure 1 inset. The C2/c phase predicted in this work is identical with the one proposed by C. J. Pickard and R. J. Needs8, which forms three-dimensional networks. Above 383 GPa, P21/c phase take over C2/c phase and becomes most competitive on enthalpy. As shown in Figure 2(a), Si atoms show a fold layered arrangement with H atoms site around them. There are four SiH4 units with five unequivalent atoms in the conventional cell. One Si atom and four H atoms occupy the crystallographic 4e position with 1 symmetry in this monoclinic crystal. The shortest distance between H atoms is 1.045 Å at 400 GPa, which is longer than the 0.762 Å of the H-H bond length in “H2” unit in the Cmca-12 structure13 of solid hydrogen at the same pressure. P21/c phase keep stable on enthalpy at least to 606 GPa until another competitive phase with C2/m symmetry appears, as shown in Figure 1. C2/m phase obtains monoclinic base-centered lattice, and contains six formula units in the conventional cell. There are three unequivalent Si atoms occupy the 4i position with m symmetry, whereas nine H atoms sit on the 8j (site symmetry is 1), 4i (site symmetry is m) and 4g (site symmetry is 2) positions respectively. The shortest distance between two H atoms is 1.009 Å, and slightly shorter than 1.045 Å in the P21/c phase. The coordination of Si atoms in C2/c, P21/c, and C2/m are all eleven, i.e. each Si atom bond with eleven H atoms, which is quite different with the molecule crystal under low pressure14 and implies some different physical characters. Detail parameters of the structures are listed in Table 1. The decomposition enthalpies reference to Cmca-1213 structure of H2 (below 500 GPa), I41/amd1315 structure of H2 (500–1000 GPa), Fm-3m16 structure of Si and C2/c17 structure of SiH3 can also be seen in Figure 1 (The comparison with SiH4(H2)2 are shown in supplementary information). It is noteworthy that the enthalpies of the three structures are lower. Moreover, P21/c and C2/m structures are found to be energetically much superior to previous structures7891112. Therefore, three monoclinic (C2/c, P21/c, and C2/m) phases can be taken as energetically stable structures of silane under high pressure range, see Figure 1.


High-temperature superconductivity in compressed solid silane.

Zhang H, Jin X, Lv Y, Zhuang Q, Liu Y, Lv Q, Bao K, Li D, Liu B, Cui T - Sci Rep (2015)

Enthalpy difference curves of Silane.Calculated enthalpies per SiH4 unit of various structures relative to our predicted Cmcm structure as a function of pressure range from 300–1000 GPa. Inset: Enthalpies in the pressure range from 310 GPa to 430 GPa.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4352889&req=5

f1: Enthalpy difference curves of Silane.Calculated enthalpies per SiH4 unit of various structures relative to our predicted Cmcm structure as a function of pressure range from 300–1000 GPa. Inset: Enthalpies in the pressure range from 310 GPa to 430 GPa.
Mentions: The crystal structures of silane were predicted with one to six SiH4 formula units per cell. Several competitive candidates for energy with the space groups C2/c (2 molecules/cell), Cmcm (2 molecules/cell), I4/mmm (3 molecules/cell), P21/c (4 molecules/cell), P21/m (4 molecules/cell), P-1 (4 molecules/cell) and C2/m (6 molecules/cell) were obtained. The enthalpies of candidates are plotted as a function of pressures in Figure 1. Above the 300 GPa, there are two competitive enthalpy structures with the C2/c and P21/c symmetry. The maximum enthalpy difference between them is only 0.01 (eV/unit cell) over the pressure range from 300 GPa to 383 GPa, see Figure 1 inset. The C2/c phase predicted in this work is identical with the one proposed by C. J. Pickard and R. J. Needs8, which forms three-dimensional networks. Above 383 GPa, P21/c phase take over C2/c phase and becomes most competitive on enthalpy. As shown in Figure 2(a), Si atoms show a fold layered arrangement with H atoms site around them. There are four SiH4 units with five unequivalent atoms in the conventional cell. One Si atom and four H atoms occupy the crystallographic 4e position with 1 symmetry in this monoclinic crystal. The shortest distance between H atoms is 1.045 Å at 400 GPa, which is longer than the 0.762 Å of the H-H bond length in “H2” unit in the Cmca-12 structure13 of solid hydrogen at the same pressure. P21/c phase keep stable on enthalpy at least to 606 GPa until another competitive phase with C2/m symmetry appears, as shown in Figure 1. C2/m phase obtains monoclinic base-centered lattice, and contains six formula units in the conventional cell. There are three unequivalent Si atoms occupy the 4i position with m symmetry, whereas nine H atoms sit on the 8j (site symmetry is 1), 4i (site symmetry is m) and 4g (site symmetry is 2) positions respectively. The shortest distance between two H atoms is 1.009 Å, and slightly shorter than 1.045 Å in the P21/c phase. The coordination of Si atoms in C2/c, P21/c, and C2/m are all eleven, i.e. each Si atom bond with eleven H atoms, which is quite different with the molecule crystal under low pressure14 and implies some different physical characters. Detail parameters of the structures are listed in Table 1. The decomposition enthalpies reference to Cmca-1213 structure of H2 (below 500 GPa), I41/amd1315 structure of H2 (500–1000 GPa), Fm-3m16 structure of Si and C2/c17 structure of SiH3 can also be seen in Figure 1 (The comparison with SiH4(H2)2 are shown in supplementary information). It is noteworthy that the enthalpies of the three structures are lower. Moreover, P21/c and C2/m structures are found to be energetically much superior to previous structures7891112. Therefore, three monoclinic (C2/c, P21/c, and C2/m) phases can be taken as energetically stable structures of silane under high pressure range, see Figure 1.

Bottom Line: Crystal structures of silane have been extensively investigated using ab initio evolutionary simulation methods at high pressures.Two metallic structures with P2₁/c and C2/m symmetries are found stable above 383 GPa.Perturbative linear-response calculations for C2/m silane at 610 GPa reveal a high superconducting critical temperature that beyond the order of 10(2) K.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Superhard Materials, College of physics, Jilin University, Changchun, 130012, P. R. China.

ABSTRACT
Crystal structures of silane have been extensively investigated using ab initio evolutionary simulation methods at high pressures. Two metallic structures with P2₁/c and C2/m symmetries are found stable above 383 GPa. The superconductivities of metallic phases are fully explored under BCS theory, including the reported C2/c one. Perturbative linear-response calculations for C2/m silane at 610 GPa reveal a high superconducting critical temperature that beyond the order of 10(2) K.

No MeSH data available.