Pressure-induced unexpected -2 oxidation states of bromine and superconductivity in magnesium bromide

High-pressure stabilization of open-shell bromine fluorides

Halogen fluorides are textbook examples of how fundamental chemical concepts, such as molecular orbital theory or the valence-shell electron-repulsion (VSEPR) model, can be used to understand the geometry and properties of compounds. However, it is still an open question whether these notions are applicable to matter subject to high pressure (>1 GPa). In an attempt to gain insight into this phenomenon, we present a computational study on the phase transitions and reactivity of bromine fluorides at pressures of up to 100 GPa (≈106 atm). We predict that at a moderately high pressure of 15 GPa, the bonding preference in the Br/F system should change considerably with BrF3 becoming thermodynamically unstable and two novel compounds emerging as stable species: BrF2 and BrF6. Calculations indicate that both these compounds contain radical molecules while being non-metallic. We propose a synthetic route for obtaining BrF2 which does not require the use of highly reactive elemental fluorine. Finally, we show how molecular orbital diagrams and the VSEPR model can be used to explain the properties of compressed bromine fluorides.

Predicted stable Li5P2 and Li4P at ambient pressure: novel high-performance anodes for lithium-ion batteries

Lithium-rich phosphides have recently attracted considerable attention due to their potential application as high-capacity and high-rate anodes for lithium-ion batteries (LIBs). However, there is still short of the promising candidate thus far because of the poor electrical conductivity or huge volume change in the already known Li-P compounds. In this work, we report two novel Li-P states, Li₅P₂ and Li₄P, stabilized under high pressures that are predicted to be quenchable down to ambient conditions by first-principles swarm structure calculations. The predicted P3m1 Li₅P₂ shows interesting features as a p-type semiconductor with an indirect band gap of 0.787 eV, possessing significant anisotropy properties in electrical transport, while R3[combining macron]m Li₄P acts as a typical electride with metallic behavior at pressures of 0-82 GPa. More importantly, our calculations reveal that the theoretical capacities of Li₅P₂ and Li₄P are predicted to reach 2164 and 3462 mA h g^-1, respectively. Combined with the good electrical transport properties, the calculated volume expansion of Li₅P₂ (130%) is found to be much smaller than those of the previously reported Li-P compounds, indicating its potential as a high performance anode material for LIBs.

Prediction of a novel robust superconducting state in TaS2 under high pressure

A novel superconducting I4/mmm phase has been predicted in TaS₂ under high pressure, illustrating an unusual superconductor–metal–superconductor transition.