The chemical composition of LK-99 approximates to Pb9Cu(PO4)6O. This implies that, in comparison with pure lead-apatite (Pb10(PO4)6O), around one quarter of Pb(II) ions situated at position 2 of the apatite structure are substituted by Cu(II) ions.
Lee et al. devised a method for the chemical synthesis of the LK-99 material by generating lanarkite from a 1:1 molar mixture of lead(II) oxide (PbO) and lead(II) sulfate (Pb(SO4)) powders, then heating at 725 °C (1,000 K; 1,340 °F) for 24 hours:
PbO + Pb(SO4) → Pb2(SO4)O
In addition, copper(I) phosphide (Cu3P) is produced by mixing copper (Cu) and phosphorus (P) powders in a 3:1 molar ratio in a sealed tube under vacuum and heated to 550 °C (820 K; 1,000 °F) for 48 hours:
Cu + P → Cu3P
The lanarkite and copper phosphide crystals are ground into a powder, placed in a sealed tube under vacuum, and heated to 925 °C (1,200 K; 1,700 °F) for between 5‒20 hours, leading to the formation of LK-99:
Pb2(SO4)O + Cu3P + O2 (g) → Pb10-xCux(PO4)6O + S (g), where (0.9 < x < 1.1)