Effects of radiation disorder in chromium spinels

Polycrystalline MgCr2O4 and CuCr2O4 samples are investigated by X-ray and neutron diffraction methods before and after irradiation by fast neutrons (En ≧ 1 MeV) of fluence 2 × 1024 m−2. It is found that under irradiation in cubic magnesium and tetragonal copper chromites with the corresponding space groups O – Fd3m and D – I4/amd different types of cations are redistributed both, over “allowed” and “forbidden” sites of the initial spinel lattice. As a result, the lattice periods and crystal symmetries are changed. The structures of the irradiated chromites may be described in terms of the space group O – Fm3m. Under annealing the irradiated samples restore their initial crystal structures. Structural changes occurring on different stages of annealing are analysed by X-ray.