A synthesis and crystal chemical study of the fast ion conductor Li _{7-3 x}Ga_xLa₃ Zr₂O₁₂ with x = 0.08 to 0.84

Fast-conducting phase-pure cubic Ga-bearing Li₇La ₃Zr₂O₁₂ was obtained using solid-state synthesis methods with 0.08 to 0.52 Ga³⁺ pfu in the garnet. An upper limit of 0.72 Ga³⁺ pfu in garnet was obtained, but the synthesis was accompanied by small amounts of La₂Zr₂O₁₂ and LiGaO₃. The synthetic products were characterized by X-ray powder diffraction, electron microprobe and SEM analyses, ICP-OES measurements, and ⁷¹Ga MAS NMR spectroscopy. The unit-cell parameter, a₀, of the various garnets does not vary significantly as a function of Ga ³⁺ content, with a value of about 12.984(4) Å. Full chemical analyses for the solid solutions were obtained giving: Li_7.08Ga _0.06La_2.93Zr_2.02O₁₂, Li _6.50Ga_0.15La_2.96Zr_2.05O ₁₂, Li_6.48Ga_0.23La_2.93Zr _2.04O₁₂, Li_5.93Ga_0.36La _2.94Zr_2.01O₁₂, Li_5.38Ga _0.53La_2.96Zr_1.99O₁₂, Li _4.82Ga_0.60La_2.96Zr_2.00O ₁₂, and Li_4.53Ga_0.72La_2.94Zr _1.98O₁₂. The NMR spectra are interpreted as indicating that Ga³⁺ mainly occurs in a distorted 4-fold coordinated environment that probably corresponds to the general 96h crystallographic site of garnet.