Synthesis and Crystal Structure of Three Ga-rich Lithium Gallides, LiGa, LiGa, and LiGa.

Three new binary phases have been synthesized in the Ga-rich part of the Li-Ga system: LiGa, LiGa, and LiGa. Their crystal structures and the respective phase formation conditions have been investigated with X-ray single crystal structure refinements, Rietveld refinements of X-ray powder diffraction data, and thermal analyses. They complete the Ga-rich part of the Li-Ga phase diagram together with the reported phases LiGa with 2 ≤ ≤ 3 and LiGa. The compositions of two of the new gallides, LiGa and LiGa, had been predicted in previous thermoanalytical studies, but their crystal structures remained unknown. All three new binary main group compounds adopt new structure types. LiGa crystallizes with the trigonal space group 3̅ (No. 167, = 6.1851(8) Å, = 23.467(4) Å), LiGa crystallizes with the hexagonal space group 6 (No. 186, = 13.7700(19) Å, = 23.250(5) Å), and LiGa crystallizes with the orthorhombic space group (No. 64, = 8.51953(4) Å, = 14.44163(7) Å, = 15.29226(7) Å). All phases form air- and moisture-sensitive crystals of bright metallic luster. They can be synthesized starting from the pure elements and taking into account their incongruent melting behavior by adequate tempering sequences derived from differential scanning calorimetry (DSC) studies of the system. Lithium gallides do not form electron-precise Zintl phases. The electronic structures of these polar intermetallic phases combine ionic, covalent, and metallic bonding contributions and have been analyzed by density functional theory (DFT) calculations in the cases of LiGa and LiGa. Measurements of the specific electronic resistivities have also been performed and prove the metallic behavior.