Superconductivity and Wilson transition behaviors of lithium-rich oxides LimO(m=1–8) under pressure based on ab initio calculations

Abstract

The study of abnormal Wilson transitions from metal to nonmetal states in simple electronic systems under high pressure plays an important role in understanding the profound physical mechanisms associated with the electronic structures of materials. Moreover, such studies serve as important references for understanding complex electronic systems. Of particular interest is that Li-O systems have been demonstrated to exhibit both normal and abnormal Wilson transition behaviors at high pressure depending on the Li to O ratio, and that Li-O compounds also exhibit superconductivity. However, the pressure-induced phase transformations and superconducting properties of these materials have not been comprehensively studied, particularly for Li-rich oxides. The present work addresses this issue by conducting ab initio structural relaxations of LimOn compounds (m≤8,n≤2) at selected pressures ranging from 1 atm to 200 GPa using density-functional theory. Accordingly, we obtain detailed structural information for all stable compounds based on their formation enthalpies with respect to decomposition into other Li-O compounds or elemental Li and O solids. The results demonstrate that the parity of m in Li-rich LimO compounds determines their metallization or antimetallization features under applied pressures rather than the magnitude of m. The C2/c phase of Li8O, which exhibits an antimetallization feature with increasing pressure, is found to be superconducting at a temperature of 5.54 K under an applied pressure of 100 GPa. In stark contrast to other Li-rich compounds and most hydrides whose superconductivity is primarily affected by the electron density of states at the Fermi level, the superconductivity of C2/c-phase Li8O is mainly affected by an increasing average electron-phonon matrix element over the Fermi surface and a decreasing average phonon frequency with increasing pressure.

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