Abstract:Si3C is predicted to take on a diamond type structure (space
group: I4̅2d), at P = 1 atm, consistent with the experimental results on a
cubic Si0.75C0.25 alloy. This structure is computed
to be a semiconductor with a direct band gap of about 1.3 eV, within
the desired values. Under pressure, Si3C may transform
to metastable metallic R3̅m-2 and R3̅m-3
structures at about 25 and 250 GPa, respectively. Both are layered
structures with six-coordinate Si and unusual six-coordinate carbon
atoms. The R3̅m-1 and R3̅m-… Show more
“…Pressure-induced increase of cation coordination number is repeatedly observed tendency 38–40 that was outlined as a general rule of high-pressure crystal chemistry in reviews of Prewitt and Downs 41 and Grochala et al (2007) 27 . In inorganic oxocompounds this tendency is typically realized along with evolution of the oxygen sublattice toward the close packing arrangements 41 .…”
Section: Discussionmentioning
confidence: 89%
“…Both experimental observations of the BeO 5 /BeO 6 configurations and ab initio calculations are in line with previous quantum chemical calculations 33–36 and demonstrate that the involvement of d orbitals is not mandatory for the formation of species with trigonal–bipyramidal and octahedral geometries. Instead, an electron-deficient multicenter bonding can be proposed as a mechanism of formation of such exotic configurations and, generally, as a densification mechanism for the CaP 2 Be 2 O 8 crystal structure adopting to high-pressure conditions 37,38 .Fig. 5Calculated total electronic density of states (DOS) of different phases of hurlbutite, CaP 2 Be 2 O 8 .…”
Beryllium oxides have been extensively studied due to their unique chemical properties and important technological applications. Typically, in inorganic compounds beryllium is tetrahedrally coordinated by oxygen atoms. Herein based on results of in situ single crystal X-ray diffraction studies and ab initio calculations we report on the high-pressure behavior of CaBe
2
P
2
O
8
, to the best of our knowledge the first compound showing a step-wise transition of Be coordination from tetrahedral (4) to octahedral (6) through trigonal bipyramidal (5). It is remarkable that the same transformation route is observed for phosphorus. Our theoretical analysis suggests that the sequence of structural transitions of CaBe
2
P
2
O
8
is associated with the electronic transformation from predominantly molecular orbitals at low pressure to the state with overlapping electronic clouds of anions orbitals.
“…Pressure-induced increase of cation coordination number is repeatedly observed tendency 38–40 that was outlined as a general rule of high-pressure crystal chemistry in reviews of Prewitt and Downs 41 and Grochala et al (2007) 27 . In inorganic oxocompounds this tendency is typically realized along with evolution of the oxygen sublattice toward the close packing arrangements 41 .…”
Section: Discussionmentioning
confidence: 89%
“…Both experimental observations of the BeO 5 /BeO 6 configurations and ab initio calculations are in line with previous quantum chemical calculations 33–36 and demonstrate that the involvement of d orbitals is not mandatory for the formation of species with trigonal–bipyramidal and octahedral geometries. Instead, an electron-deficient multicenter bonding can be proposed as a mechanism of formation of such exotic configurations and, generally, as a densification mechanism for the CaP 2 Be 2 O 8 crystal structure adopting to high-pressure conditions 37,38 .Fig. 5Calculated total electronic density of states (DOS) of different phases of hurlbutite, CaP 2 Be 2 O 8 .…”
Beryllium oxides have been extensively studied due to their unique chemical properties and important technological applications. Typically, in inorganic compounds beryllium is tetrahedrally coordinated by oxygen atoms. Herein based on results of in situ single crystal X-ray diffraction studies and ab initio calculations we report on the high-pressure behavior of CaBe
2
P
2
O
8
, to the best of our knowledge the first compound showing a step-wise transition of Be coordination from tetrahedral (4) to octahedral (6) through trigonal bipyramidal (5). It is remarkable that the same transformation route is observed for phosphorus. Our theoretical analysis suggests that the sequence of structural transitions of CaBe
2
P
2
O
8
is associated with the electronic transformation from predominantly molecular orbitals at low pressure to the state with overlapping electronic clouds of anions orbitals.
“…In addition to 2D SiC, other compositions of silicon carbide, i.e., 2D SixCy, are also energetically favorable. Thermodynamic and kinetic stability of 2D SixCy compositions have also been investigated [ 3 , 23 , 32 , 33 , 34 , 35 , 36 , 37 ]. All theoretical studies confirm that 1:1 stoichiometry, i.e., SiC, is the most stable composition.…”
This paper reports the successful synthesis of true two-dimensional silicon carbide using a top-down synthesis approach. Theoretical studies have predicted that 2D SiC has a stable planar structure and is a direct band gap semiconducting material. Experimentally, however, the growth of 2D SiC has challenged scientists for decades because bulk silicon carbide is not a van der Waals layered material. Adjacent atoms of SiC bond together via covalent sp3 hybridization, which is much stronger than van der Waals bonding in layered materials. Additionally, bulk SiC exists in more than 250 polytypes, further complicating the synthesis process, and making the selection of the SiC precursor polytype extremely important. This work demonstrates, for the first time, the successful isolation of 2D SiC from hexagonal SiC via a wet exfoliation method. Unlike many other 2D materials such as silicene that suffer from environmental instability, the created 2D SiC nanosheets are environmentally stable, and show no sign of degradation. 2D SiC also shows interesting Raman behavior, different from that of the bulk SiC. Our results suggest a strong correlation between the thickness of the nanosheets and the intensity of the longitudinal optical (LO) Raman mode. Furthermore, the created 2D SiC shows visible-light emission, indicating its potential applications for light-emitting devices and integrated microelectronics circuits. We anticipate that this work will cause disruptive impact across various technological fields, ranging from optoelectronics and spintronics to electronics and energy applications.
“…Examples include elemental carbon, which has been predicted to become six-fold coordination at terapascal pressures, 50,51 and high pressure Si-C compounds such as rocksalt SiC, 52,53 and two predicted Si 3 C phases. 54 More relevant to the C-S-H system are carbon atoms bonded to more than four hydrogen atoms such as the nonclassical carbocation, C s -CH + 5 , which contains three short and two long C-H bonds. It can be viewed as a proton inserted into one of the σ C-H bonds within methane, forming a three-center two-electron (3c-2e) bond between one carbon and two hydrogen atoms.…”
First-principles calculations were carried out to provide a chemical basis for proposed structures associated with the recently reported room-temperature superconductivity in a carbonaceous sulfur hydride material under pressure. Calculations were performed on supercells of H 3 S doped with 1.85-25% carbon, corresponding to SH 3 → CH 3 or SH 3 → CH 4 substitutions, primarily at pressures of 270 GPa where the maximum critical temperature, T c , has been reported. In the first type of substitution, the carbon atoms can be six-fold coordinated, stabilizing a CH 6 configuration within the cubic H 3 S framework structure that forms under pressure. In the second, the carbon can be four-fold coordinated as methane intercalated into the H-S lattice, with or without an additional hydrogen in the framework. The results indicate that unusual local bonding configurations with respect to carbon can be stabilized under pressure. The doping breaks degenerate bands, lowering the density of states at the Fermi level (N F ), and localizing electrons in C-H bonds. Low levels of CH 4 doping do not increase N F 1
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