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