The Exotically Stoichiometric Compounds and Superconductivity of Lithium-Copper Systems under High Pressure.

Pressure, as a useful tool, can push elements to new oxidation states by altering the stoichiometry of compounds, leading to materials with exotic physical and chemical properties. Herein, structure searches for Li-Cu systems were carried out under pressure. Three Li-rich Li-Cu compounds with exotic stoichiometries (i.e., Li4Cu, Li5Cu, and Li6Cu) are predicted at high pressure. Remarkably, the Li6Cu consists of a Cu-centered face-sharing icosahedron. Further simulations reveal that the captured electrons from Li atoms prompt Cu atoms to achieve high negative oxidation states beyond -1 and to act as a 4p group element. Moreover, our results unravel the superconductivity of the Li-rich Li-Cu system and the R3̅ phase of Li6Cu with Tc of ∼15 K at 50 GPa. The present results can greatly improve the understanding of the exotic electronic behavior of Li-Cu systems under high pressure.