Exceptional metal–semiconductor–metal transition of lead apatites via oxygen defect tuning

Abstract

Lead apatites, distinguished and compelling bulk materials with the stoichiometric arrangement as Pb₁₀(PO_x)₆O_y, are renowned for their structural complexity. Recently, the discovery of possible room-temperature superconductivity under ambient pressure in copper-substituted lead apatites has engendered considerable interest within both the physics community and beyond. Nevertheless, exploration of pristine Pb₁₀(PO_x)₆O_y parent structures has hitherto remained elusive. In this study, we employ density functional theory (DFT) calculations to investigate the effects of oxygen defects on the electronic structures of Pb₁₀(PO_x)₆O_y and Pb₉Cu(PO_x)₆O_y. We scrutinize two distinct categories of defects: oxygen atoms enmeshed within PO_x groups (O_x) and solitary oxygen atoms (O_y). Our investigation uncovers a profound influence of these defects on the band structure. Specifically, the introduction of O_y defects prompts a remarkable transition in Pb₁₀(PO₄)₆O_y from a metal to semiconductor to metal state, accompanied by pivotal shifts in the principal electronic contributors from p orbitals of O_y to those of Pb atoms. Furthermore, the introduction of O_x defects in Pb₁₀(PO_x)₆O₁ engenders metamorphosis in the band structure, transmuting it from a semiconductor to a metallic state. Significantly, our findings pinpoint the suitable range of x in the Pb₁₀(PO_x)₆O₁ configuration as lying between 2 and 4. Additionally, our study also demonstrates that the oxygen defects (O_x/O_y) do not affect the metallic properties of copper-substituted lead apatites. This study elucidates the significant role of oxygen defects in modulating the electronic properties of apatite materials, offering insights into potential interdisciplinary applications. This establishes a crucial link between material composition and electronic behavior, revealing key mechanisms for engineering functionality in lead apatites and other advanced materials.