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Researchers recently synthesized a new orthorhombic allotrope of silicon, namely Cmcm Si24. This work studied the effect of one vacancy for Cmcm Si24 on structural, electronic, and mechanical anisotropy properties by the first principle calculation. The lattice parameters of Cmcm Si24:V are the same as Cmcm Si24, but the density of Cmcm Si24:V is larger than that of Cmcm Si24. Moreover, the values of elastic moduli for Cmcm Si24:V are smaller than for Cmcm Si24. The Cmcm Si24:V has mechanical stability and anisotropy and has lower formation energy than diamond-Si. The analysis of the band structures shows that Cmcm Si24 is an indirect band gap material, and the value of the band gap is 1.08 eV. In particular, electronic band structures of Cmcm Si24:V exhibit metallic characteristics. Furthermore, the electron localization function indicated strong covalent silicon--silicon bonds in Cmcm Si24 and Cmcm Si24:V. In addition, the effective mass of electrons and holes of Cmcm Si24 is smaller than that of diamond-Si along the a direction, and larger than that along the b and c directions. Finally, the X-ray diffraction patterns for Cmcm Si24 and Cmcm Si24:V are very close after 13:84°. [ABSTRACT FROM AUTHOR]

Researchers recently synthesized a new orthorhombic allotrope of silicon, namely Cmcm Si24. This work studied the effect of one vacancy for Cmcm Si24 on structural, electronic, and mechanical anisotropy properties by the first principle calculation. The lattice parameters of Cmcm Si24:V are the same as Cmcm Si24, but the density of Cmcm Si24:V is larger than that of Cmcm Si24. Moreover, the values of elastic moduli for Cmcm Si24:V are smaller than for Cmcm Si24. The Cmcm Si24:V has mechanical stability and anisotropy and has lower formation energy than diamond-Si. The analysis of the band structures shows that Cmcm Si24 is an indirect band gap material, and the value of the band gap is 1.08 eV. In particular, electronic band structures of Cmcm Si24:V exhibit metallic characteristics. Furthermore, the electron localization function indicated strong covalent silicon--silicon bonds in Cmcm Si24 and Cmcm Si24:V. In addition, the effective mass of electrons and holes of Cmcm Si24 is smaller than that of diamond-Si along the a direction, and larger than that along the b and c directions. Finally, the X-ray diffraction patterns for Cmcm Si24 and Cmcm Si24:V are very close after 13:84°. [ABSTRACT FROM AUTHOR]

A total of 87 new monoclinic silicon allotropes are systematically scanned by a random strategy combined with group and graph theory and high-throughput calculations. The new allotropes include 13 with a direct or quasi-direct band gap and 12 with metallic characteristics, and the rest are indirect band gap semiconductors. More than 30 of these novel monoclinic Si allotropes show bulk moduli greater than or equal to 80 GPa, and three of them show even greater bulk moduli than diamond Si. Only two of the new Si allotropes show a greater shear modulus than diamond Si. The crystal structures, stability (elastic constants, phonon spectra), mechanical properties, electronic properties, effective carrier masses and optical properties of all 87 Si monoclinic allotropes are studied in detail. The electron effective masses ml of five of the new allotropes are smaller than that of diamond Si. All of these novel monoclinic Si allotropes show strong absorption in the visible spectral region. Taken together with their electronic band gap structures, this makes them promising materials for photovoltaic applications. These investigations greatly enrich the current knowledge of the structure and electronic properties of silicon allotropes.

[Display omitted] • We used RG2 associated with high-throughput screening method to find out more stable silicon allotropes. • The discovered structures have good stabilities, mechanical properties and electronic properties. • Some of Structures have suitable band gaps and strong absorption, which will be useful in future experiments and photovoltaic applications. Silicon is the fundamental material for the semiconductor and microelectronics industries, but controlling the electronic band gap structure of diamond-type silicon remains a huge challenge to adapt to growing applications. Here, we have predicated 23 new silicon allotropes in space group P 2/ m from 279 possible structures by high-throughput screening accompanied by graph and group theory based on random strategy (RG2) code. The mechanical, electronic and optical properties of these structures were studied in detail. These novel silicon allotropes demonstrate various electronic structures, including metal, direct/quasi direct bandgap structure, and indirect bandgap structures. These new silicon allotropes demonstrate various electronic structures, including metal, direct/quasi direct bandgap structure, and indirect bandgap structures. Besides different electronic bandgap structures, all 23 structures exhibit strong absorption in the visible light region and P2/m-15 demonstrates the excellent mechanical properties (Bulk modulus beyond 80 GPa). Based on their nice stability, good mechanical, electronic and optical properties validated by the ab inito molecular dynamics simulation, phonon spectra and density functional theoretical calculations, these predicted silicon allotropes provide not only ideas for the synthesis of new silicon allotropes but also dawn for expanding the application of semiconductor materials. [ABSTRACT FROM AUTHOR]

A total of 87 new monoclinic silicon allotropes are systematically scanned by a random strategy combined with group and graph theory and high-throughput calculations. The new allotropes include 13 with a direct or quasi-direct band gap and 12 with metallic characteristics, and the rest are indirect band gap semiconductors. More than 30 of these novel monoclinic Si allotropes show bulk moduli greater than or equal to 80 GPa, and three of them show even greater bulk moduli than diamond Si. Only two of the new Si allotropes show a greater shear modulus than diamond Si. The crystal structures, stability (elastic constants, phonon spectra), mechanical properties, electronic properties, effective carrier masses and optical properties of all 87 Si monoclinic allotropes are studied in detail. The electron effective masses m l of five of the new allotropes are smaller than that of diamond Si. All of these novel monoclinic Si allotropes show strong absorption in the visible spectral region. Taken together with their electronic band gap structures, this makes them promising materials for photovoltaic applications. These investigations greatly enrich the current knowledge of the structure and electronic properties of silicon allotropes., (open access.)

Element silicon can form many allotropes due to its sp3-hybridization and its ground state phase in 3C stacking order (Si-I) is the material pioneer of solar cells and the material basis for micro-electronics. In this work, we proposed five new silicon allotropes (5H, 6H-2, 7H-1, 7H-2 and 7H-3) with similar stacking manners to Si-I but in different orders by random sampling strategy combined with group and graph theory (RG2). The calculated total energies of these five new silicon allotropes are just a few meV/atom higher than that of the Si-I and all of them are confirmed to be both dynamically and mechanically stable based on their vibrational and mechanical properties. The crystalline structures and fundamental physical properties discussed in present work are useful for future experiments to explain potential hexagonal silicon allotropes beyond 3C. [Display omitted] [ABSTRACT FROM AUTHOR]

Silicon is essential for today's electronics because of its ability to show various electronic behaviors that are relevant to numerous fields of cutting-edge applications. It is not a pollutant and, therefore, an ideal candidate to replace the actual materials in photovoltaics, such as compounds based on the arsenic and heavy metals. However, conventional diamond-like Si is an indirect gap semiconductor and cannot absorb solar photons directly. This justifies intensive theoretical and experimental research for the direct-bandgap forms of silicon. Our recent high-pressure studies of the chemical interaction and phase transformations in the Na-Si system, revealed a number of interesting routes to new and known silicon compounds and allotropes. The pressure-temperature range of their formation is suitable for large-volume synthesis and future industrial scaling. The variety of properties observed (e.g. quasi-direct bandgap of open-framework allotrope Si 24 ) allows us to suggest future applications. [ABSTRACT FROM AUTHOR]

The structural mechanical properties and electronic properties of a new silicon allotrope Si96 are investigated at ambient pressure by using a first-principles calculation method with the ultrasoft pseudopotential scheme in the framework of generalized gradient approximation. The elastic constants and phonon calculations reveal that Si96 is mechanically and dynamically stable at ambient pressure. The conduction band minimum and valence band maximum of Si96 are at the R and G point, which indicates that Si96 is an indirect band gap semiconductor. The anisotropic calculations show that Si96 exhibits a smaller anisotropy than diamond Si in terms of Young's modulus, the percentage of elastic anisotropy for bulk modulus and shear modulus, and the universal anisotropic index AU. Interestingly, most silicon allotropes exhibit brittle behavior, in contrast to the previously proposed ductile behavior. The void framework, low density, and nanotube structure make Si96 quite attractive for applications such as hydrogen storage and electronic devices that work at extreme conditions, and there are potential applications in Li-battery anode materials. [ABSTRACT FROM AUTHOR]

The figure represent convex hull of Rb-Si system at 10 GPa, crystal structure of the lowest energy compound, novel silicon allotrope after removing Rb atoms and corresponding electronic and optical properties. [Display omitted] Using a global structure prediction method, we explored the structures, stability, and electronic properties of binary Rb-Si compounds under high pressure. We identified eight rubidium silicides, which are dynamically stable in their stable pressure region. We also identified five novel silicon allortopes via removing the Rb atoms from the predicted Rb-Si compounds. Two new silicon allotropes, Cmcm -Si and C 2/ m- Si, were first proposed, which are both dynamically and mechanically stable. Electronic structure calculations reveal that Cmcm- Si is a semiconductor with direct bandgap and C 2/ m- Si exhibits metallicity. Besides, the Cmcm -Si phase demonstrates that its optical properties are superior to that of dia -Si, indicating it could be a promising photovoltaic material. The present results expand the high pressure phases of Rb-Si compounds and provide insights for exploring other alkali silicides with open channels. [ABSTRACT FROM AUTHOR]

Silicon is the most basic and commonly used semiconductor material in the modern microelectronics industry. Because diamond silicon is an indirect band gap semiconductor, its application in the optoelectronic industry is limited. Searching for new silicon allotropes with direct band gaps has been a hot topic in the fields of condensed matter and materials science. In this work, the elastic anisotropy and thermal conductivity of seven silicon allotropes with direct band gaps (D76, D63, D135, D243, D12, D239, and D979), a silicon allotrope with quasi-direct band gap (Q135) and a silicon allotrope with indirect band gap (I926) are investigated. The elastic anisotropy of shear modulus, Young's modulus and Poisson's ratio for Q135, D76, D63, D135, D243, D12, I926, D239, and D979 silicon allotropes are investigated by surface constructions of the 2D representation. The I926 phase has the greatest thermal conductivity among the nine silicon allotropes, and it is greater than that of the oC12 phase. In addition, the anisotropy of elastic moduli and the anisotropy of thermal conductivity in each main plane for Q135, D76, D63, D135, D243, D12, I926, D239, and D979 are studied for the first time. [ABSTRACT FROM AUTHOR]

The structural mechanical properties and electronic properties of a new silicon allotrope Si 96 are investigated at ambient pressure by using a first-principles calculation method with the ultrasoft pseudopotential scheme in the framework of generalized gradient approximation. The elastic constants and phonon calculations reveal that Si 96 is mechanically and dynamically stable at ambient pressure. The conduction band minimum and valence band maximum of Si 96 are at the R and G point, which indicates that Si 96 is an indirect band gap semiconductor. The anisotropic calculations show that Si 96 exhibits a smaller anisotropy than diamond Si in terms of Young's modulus, the percentage of elastic anisotropy for bulk modulus and shear modulus, and the universal anisotropic index A . Interestingly, most silicon allotropes exhibit brittle behavior, in contrast to the previously proposed ductile behavior. The void framework, low density, and nanotube structure make Si U . Interestingly, most silicon allotropes exhibit brittle behavior, in contrast to the previously proposed ductile behavior. The void framework, low density, and nanotube structure make Si 96 quite attractive for applications such as hydrogen storage and electronic devices that work at extreme conditions, and there are potential applications in Li-battery anode materials.