A new phase in the system lithium–aluminum: Characterization of orthorhombic Li2Al

Investigation of the Li rich part of the binary Li–Al system revealed the existence of a new phase, orthorhombic Li2Al, which is isostructural to Li2Ga and Li2In. The crystal structure was determined from single crystal X-ray diffraction data (Cmcm, a=4.658(2) Å, b=9.767(4) Å, c=4.490(2) Å, Z=4). Refinement of atomic position site occupancies yielded a composition Li1.92Al1.08 (64 at% Li) indicating a small homogeneity range, Li2−xAl1+x. Li2Al is the peritectic decomposition product of the stoichiometric compound Li9Al4, which is stable below 270±2 °C. Li2Al itself decomposes peritectically to Li3Al2 and Li rich melt at 335±2 °C. The discovery of Li2Al (Li2−xAl1+x) settles a long standing inconsistency in the Li–Al phase diagram which was based on the assumption that Li9Al4 possesses a high temperature modification.