Abstract
The fast Li‐conducting intermetallic compound, 
, crystallizes in the Zintl structure (B32 prototype: 
). A high concentration of constitutional vacancy defects is responsible for the Li conduction. The lattice constant, thermal parameters, and the order parameter have been determined by neutron diffraction as a function of temperature. The results show a high concentration of anti‐site defects (both Li on the Al sublattice and Al on the Li sublattice) at elevated temperatures. The high concentrations of vacancies and anti‐site defects suggest a very complex conduction mechanism at elevated temperatures.