Synthesis and Crystal Structure of Three Ga-rich Lithium Gallides, LiGa₆, Li₁₁Ga₂₄, and LiGa₂

Three new binary phases have been synthesized in the Ga-rich part of the Li-Ga system: LiGa₆, Li₁₁Ga₂₄, and LiGa₂. 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 Li_6-Ga₁₄ with 2 ≤ x ≤ 3 and LiGa_3.42. The compositions of two of the new gallides, LiGa₆ and LiGa₂, had been predicted in previous thermoanalytical studies, but their crystal structures remained unknown. All three new binary main group compounds adopt new structure types. LiGa₆ crystallizes with the trigonal space group R3̅c (No. 167, a = 6.1851(8) Å, c = 23.467(4) Å), Li₁₁Ga₂₄ crystallizes with the hexagonal space group P6₃mc (No. 186, a = 13.7700(19) Å, c = 23.250(5) Å), and LiGa₂ crystallizes with the orthorhombic space group Cmce (No. 64, a = 8.51953(4) Å, b = 14.44163(7) Å, c = 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 LiGa₆ and LiGa₂. Measurements of the specific electronic resistivities have also been performed and prove the metallic behavior.