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The stability, electronic structure, and potential superconductivity in AB3Si3 (A = Na, K, Rb, and Cs) compounds that assume a clathrate-based sodalite structure whose framework consists of covalent B–Si bonds are investigated via first-principles calculations. This structure type has recently been predicted in a number of high-temperature superconducting hydrides, but these are only stable under megabar pressures. Herein, we predict a novel superconducting phase, RbB3Si3, that could be synthesized under pressures that are smaller by a factor of 10, ∼10 GPa, and quenched to atmospheric conditions. Electron–phonon coupling calculations predict that RbB3Si3 possesses a superconducting critical temperature, T c, of 14 K at 1 atm. The dynamic stability of RbB3Si3 and CsB3Si3 at ambient pressure can be explained by considering the chemical pressure exerted on the B–Si framework that is caused by the size effect of the alkali metal atom.

A recently newly synthesized monochalcogenide, γ-GeSe, is demonstrated for 2 potential application of Li exfoliation and lithium-ion battery with the Li species showing a small diffusion barrier of 0.21 eV and the voltage ranging from 0.071-0.015 V. The theoretical storage capacity of γ-GeSe is over 530.36 mAh g -1 . Such results suggest the γ-GeSe nanosheet can be a promising anode material for lithiumion battery.

Germanium selenide (GeSe) is a unique two-dimensional (2D) material showing various polymorphs stable at ambient conditions. Recently, a new phase with a layered hexagonal lattice (γ-GeSe) was synthesized with ambient stability and extraordinary electronic conductivity, even higher than that of graphite, while its monolayer is semiconducting. In this work, using first-principles derived force constants and the Boltzmann transport theory, we explore the lattice thermal conductivity (κl) of monolayer γ-GeSe, together with a comparison with monolayer α-GeSe and β-GeSe. The κl of the γ-phase is relatively low (5.50 W/mK), comparable with those of α- and β-phases. The acoustic branches in α-GeSe are well separated from the optical branches, limiting scattering channels in the phase space, while for β-GeSe and γ-GeSe, the acoustic branches are resonant with the low-frequency optical branches, facilitating more phonon–phonon scattering. For γ-GeSe, the cumulative κl is isotropic and the phononic representative mean free path (rMFP) is the shortest (17.07 nm) among the three polymorphs, indicating that the κl of the γ-phase is less likely to be affected by the size of the sample, while for α-GeSe, the cumulative κl grows slowly with the mean free path and the rMFP is longer (up to 20.56 and 35.94 nm along zigzag and armchair directions, respectively), showing a stronger size dependence of κl. Our work suggests that GeSe polymorphs with overall low thermal conductivity are promising contenders for thermoelectric and thermal management applications.

The study of two-dimensional (2D) materials has attracted considerable attention owing to their unique but fascinating properties. Here we systematically explored 2D carbon nitride monolayer sheets via the particle swarm optimization algorithm in combination with density functional theory. As a result of structural searches, four carbon nitride monolayers are predicted with stable stoichiometries of C5N2, C2N, C3N2 and CN. These predicted structures are semiconductors with an optimal band gap for solar cell application as indicated in our electronic simulations. Our current results also reveal the high tensile strengths of the predicted structures compared to known porous carbon nitride monolayer sheets. This work may provide a route for the design of 2D candidates in the application of photovoltaic materials.