Superconducting Open-Framework Allotrope of Silicon at Ambient Pressure

Preparation of a Silicon/MXene Composite Electrode by a High-Pressure Forming Method and Its Application in Li+-Ion Storage

The main component of high-capacity silicon-based electrodes is silicon powder, which necessitates intricate processing to minimize volume growth and powder separation while guaranteeing the ideal Si content. This work uses the an situ high-pressure forming approach to create an MXene/m-Si/MXene composite electrode, where MXene refers to Ti3C2TX, and m-Si denotes two-phase mixed nano-Si particles. The sandwich shape promotes silicon's volume growth and stops active particles from spreading. The conductive structure of Ti3C2TX MXene increases the efficiency of charge transfer while reducing internal resistance. After 100 cycles, the composite electrode's original capacity of 1310.9 mAh g-1 at a current density of 0.5 A g-1 is maintained at 781.0 mAh g-1. These findings lay the foundation for further investigations into Si matrix composite electrodes.

Route to a direct-gap silicon allotrope Si32

Using swarm-intelligence-based structure prediction methods, we predict a novel direct bandgap silicon allotrope with open channels at ambient conditions. This silicon phase, termed Si₃₂, can be produced by removing Sr atoms from a newCmcm-SrSi₈clathrate-like compound, which is calculated to be thermodynamically stable under epitaxial strain at high pressures. Si₃₂is predicted to have a direct bandgap of ∼1.15 eV and exceptional optical properties. The prediction of novel silicon clathrate-like structure paves the way for the exploration of novel silicon phases with extensive application possibilities.

Stable Structures and Superconductivity in a Y-Si System under High Pressure

Recently, the discovery of superconductivity in compressed electrides offers a promising route toward searching for high superconductivity in a high-pressure community. However, only a few superconducting electrides have been successfully found thus far, thereby limiting the variety of superconducting electride examples. In this work, we performed extensive structure searches on a high-pressure Y-Si system by using CALYPSO structure prediction methodology. Our simulations identified several stable stoichiometries of YSi, YSi₂, YSi₃, Y₅Si₃, Y₂Si, and Y₃Si under high pressure. These structures contain a diversity of structure configurations, including silicon chains, Si₃ trilaterals, Si₄ quadrilaterals, Si₆ hexagons, Si₈ rings, a Si₄-Si₆-Si₈ frame, as well as a silicon layer. Remarkably, Y₃Si is predicted to be an electride with a superconducting critical temperature (T_c) of ∼11.2 and 14.5 K at 30 and 50 GPa, respectively. These results highlight the role of the electrons at the Fermi surface in determining the superconductivity of predicted structures.

Predicted CsSi compound: a promising material for photovoltaic applications

Exploration of photovoltaic materials has received enormous interest for a wide range of both fundamental and applied research. Therefore, in this work, we identify a CsSi compound with a Zintl phase as a promising candidate for photovoltaic material by using a global structure prediction method. Electronic structure calculations indicate that this phase possesses a quasi-direct band gap of 1.45 eV, suggesting that its optical properties could be superior to those of diamond-Si for capturing sunlight from the visible to the ultraviolet range. In addition, a novel silicon allotrope is obtained by removing Cs atoms from this CsSi compound. The superconducting critical temperature (T_c) of this phase was estimated to be of 9 K in terms of a substantial density of states at the Fermi level. Our findings represent a new promising CsSi material for photovoltaic applications, as well as a potential precursor of a superconducting silicon allotrope.

All-Silicon Topological Semimetals with Closed Nodal Line

Because of the natural compatibility with current semiconductor industry, silicon allotropes with diverse structural and electronic properties provide promising platforms for next-generation Si-based devices. After screening 230 all-silicon crystals in the zeolite frameworks by first-principles calculations, we disclose two structurally stable Si allotropes (AHT-Si₂₄ and VFI-Si₃₆) containing open channels as topological node-line semimetals with Dirac nodal points forming a nodal loop in the k _z = 0 plane of the Brillouin zone. Interestingly, their nodal loops protected by inversion and time-reversal symmetries are robust against SU(2) symmetry breaking because of the very weak spin-orbit coupling of Si. When the nodal lines are projected onto the (001) surface, flat surface bands can be observed because of the nontrivial topology of the bulk band structures. Our discoveries extend the topological physics to the three-dimensional Si materials, highlighting the possibility of realizing low-cost, nontoxic, and semiconductor-compatible Si-based electronics with topological quantum states.

Structural diversity and electronic properties in potassium silicides

Stable potassium silicides in the complete compositional landscape were systematically explored up to 30 GPa using the variable-composition evolutionary structure prediction method. The results show that K₄Si, K₃Si, K₅Si₂, K₂Si, K₃Si₂, KSi, KSi₂, KSi₃, and K₈Si₄₆ have their stability fields in the phase diagram. The spatial dimensional diversity of polymerized silicon atoms (0D "isolated" anion, dimer, Si₄ group, 1D zigzag chain, 2D layer, and 3D network) under the potassium sublattice was uncovered as silicon content increases. Especially, the 2D layered silicon presents interestingly a variety of shapes, such as the "4 + 6" ring, "4 + 8"ring, and 8-membered ring. K-Si bonding exhibits a mixed covalency and ionicity, while Si-Si bonding is always of covalent character. Semiconductivity or metallicity mainly depends on the form of sublattices and K:Si ratio, which allows us to find more semiconductors in the Si-rich side when closed-shell K cations are encompassed by polymerized Si. The semiconducting silicides present strong absorption in the infrared and visible light range. These findings open up the avenue for experimental synthesis of alkali metal-IVA compounds and potential applications as battery electrode materials or photoelectric materials.