Defect structure of β-LiAl

Abstract

Lattice parameter and density measurements have been made on a series of Li-Al alloys extending over the LiAl β-phase. The lattice parameter of the slowly cooled β-phase alloys varied almost linearly with composition within the phase field. Theoretical density calculations for several single-defect models from lattice parameter data did not yield a good fit with the experimental density data. Rather, a model based on the coexistence of two types of defects, namely, vacancies in the lithium sublattice and lithium antistructure atoms in the aluminum sublattice, characterized the defect structure. Calculated concentrations of these defects varied with departure from stoichiometry and showed good agreement with the concentration of lithium vacancies estimated from NMR measurements. Compositional dependence of the vacancy concentration and the lithium diffusion coefficient produced a good correlation and strongly suggested that the lithium atoms diffuse via a vacancy mechanism. It is hypothesized that the defect structure of this compound may be related to the electronic structure of this so-called NaTl phase.