RADIATION EFFECTS ON LI-VACANCY ORDERING IN BETA-LIAL

Radiation effects on the Li-vacancy ordering in beta-LiAl [NaTl struct ure (space group Fd3m)] have been studied by Li-ion irradiation. The L i-vacancy ordering in beta-Li0.50Al0.50 was destroyed by the irradiati on, 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 irradi ation, 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 pai r, and an aluminum interstitial and Al vacancy pair. The latter defect is important for an annealing stage above the Li-vacancy ordering tem perature. These defects disappeared completely by annealing at room te mperature.