Models of Oxygen Occupancy in Lead Phosphate Apatite Pb10(PO4)6O

Lead phosphate apatite, the parent compound of the proposed room-temperature superconductor LK-99, features a [Pb10(PO4)6]II scaffold with a charge-compensating oxide ion. This O–II occupies a 4e site in the P63/m unit cell, with 25% probability on average. We model the occupancy of this site from substoichiometric (x = 0) to superstoichiometric (x = 4) regimes in Pb10(PO4)6Ox. Doping is predicted by adjusting the oxygen composition within the ⟨0001⟩ channel, with evidence for strong O–O correlation. This behavior introduces a sensitivity to the crystal growth and annealing conditions, with an opportunity for novel functionality to emerge.