A Synthesis and Crystal Chemical Study of the Fast Ion Conductor Li _{7–3 x} Ga _x La ₃ Zr ₂O ₁₂ with x = 0.08 to 0.84

Abstract

Fast-conducting phase-pure cubic Ga-bearing Li ₇La ₃Zr ₂O ₁₂ was obtained using solid-state synthesis methods with 0.08 to 0.52 Ga ³⁺ pfu in the garnet. An upper limit of 0.72 Ga ³⁺ pfu in garnet was obtained, but the synthesis was accompanied by small amounts of La ₂Zr ₂O ₁₂ and LiGaO ₃. 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, a ₀, 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 _2.02O ₁₂, Li _6.50Ga _0.15La _2.96Zr _2.05O ₁₂, Li _6.48Ga _0.23La _2.93Zr _2.04O ₁₂, Li _5.93Ga _0.36La _2.94Zr _2.01O ₁₂, Li _5.38Ga _0.53La _2.96Zr _1.99O ₁₂, Li _4.82Ga _0.60La _2.96Zr _2.00O ₁₂, and Li _4.53Ga _0.72La _2.94Zr _1.98O ₁₂. The NMR spectra are interpreted as indicating that Ga ³⁺ mainly occurs in a distorted 4-fold coordinated environment that probably corresponds to the general 96 h crystallographic site of garnet.

Abstract

Fast-conducting cubic Ga-bearing Li ₇La ₃Zr ₂O ₁₂ (LLZO) has been synthesized using solid-state methods with 0.08 to 0.52 Ga ³⁺ pfu in the garnet. An upper limit of 0.72 Ga ³⁺ pfu in the garnet was obtained, but the synthesis product contained small amounts of La ₂Zr ₂O ₁₂ and LiGaO ₃. The NMR spectra are interpreted as indicating that Ga ³⁺ mainly occurs in a distorted 4-fold coordinated environment that corresponds to the “non-standard” general 96 h crystallographic site.