Atomic ordering and lattice distortion in the zirconium–oxygen alloys with 28.2 and 29.2 at.% oxygen

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 a₀ and c₀ of the host hexagonal metal lattice by a = √3a₀ and c = c₀. 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 [epsilon]-Fe₂N. 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.