RADIATION EFFECTS ON LI-VACANCY ORDERING IN BETA-LIAL

Radiation effects on the Li-vacancy ordering in beta-LiAl [NaTl structure (space group Fd3m)] have been studied by Li-ion irradiation. The Li-vacancy ordering in beta-Li0.50Al0.50 was destroyed by the irradiation, indicating a relatively weak interaction between the Li vacancies that originate from the long-range ordering. On the other hand, the Li-vacancy ordering in beta-Li0.48Al0.52 was not collapsed by the irradiation, suggesting a relatively strong interaction between Li vacancies. This is responsible for the body-centered-tetragonal arrangement of Li vacancies observed in neutron-diffraction studies. The increase in the residual resistivity after the irradiation suggests the existence of two Frenkel-type defects: a lithium interstitial and Li vacancy pair, and an aluminum interstitial and Al vacancy pair. The latter defect is important for an annealing stage above the Li-vacancy ordering temperature. These defects disappeared completely by annealing at room temperature.