The structure of the interstitially ordered lattice formed in zirconium-oxygen alloys has been studied with use of single-crystal data obtained by X-ray and neutron diffraction methods. The structure belongs to space group P312 and the lattice parameters a and c are related to a_0 and c_0 of the host hexagonal metal lattice by a=v3a_0 and c=c_0. The ordered arrangement of interstitial oxygen atoms is described as a regular stacking of layers parallel to the (00.1) plane with the sequence (AC)B(AC)B…, which is of the same type as that of nitrogen atoms in ε-Fe_2N. The occupancy probability of oxygen atoms is high for interstitial sites of the A and B types while it is low for sites of the C type. The host metal lattice is distorted in such a way that spacings of successive (00.2) planes are not the same and a hexagonal network of atoms in these planes is periodically deformed
