As with the other aluminate systems, the binary Li2O-Al2O3 is characterized by the two refractory oxide end-members, Li2O (which melts at 1,000°C) and Al2O3. There are three stable compounds in the Li2O-Al2O3 system: Li5AlO4, LiAlO2, and LiAl5O8. The phases of most interest for materials application are the LiAlO2 compounds that have a, P, and Y form (Fig. 3). The a-LiAlO2 is orthorhombic and has the space group r3m, while the Y form has even lower (tetragonal) symmetry. Both Li and Al are in tetrahedral coordination in the y phase. The y phase can be produced irreversibly by sintering the a
AI2O3 % m
Fig. 3 The Li2O-Al2O3 phase diagram 
phase at 1,350°C. The lattice parameters of LiAlO2 match closely those of gallium nitrides, and lithium aluminates are used as a substrate for GaN epitaxial films.