ChemInform Abstract: Crystal Chemistry and Stability of “Li₇La₃Zr₂O₁₂” Garnet: A Fast Lithium‐Ion Conductor.

Abstract

Garnet: A Fast Lithium-IonConductor. -Single crystals of the title compound are prepared by sintering mixtures of ZrO2, La2O3, and Li2CO3 using ceramic crucibles in initial steps and later sealed Pt capsules. The samples contain small amounts of Al, probably originating from the crucibles. Li7La3Zr2O12 crystallizes in the cubic space group Ia3d with Z = 8 (single crystal XRD) between 100 and 500 K. Li atoms are located on at least two structural sites that are partially occupied, while other Li atoms in the structure appear to be delocalized. Li NMR spectroscopy indicates fast Li ion diffusion at room temperature. Using solely Pt crucibles during sintering a tetragonal Li7La3Zr2O12 room temp. phase (powder XRD) is obtained which undergoes a phase transition to a cubic phase between 100 and 150°C. Cubic "Li 7 La 3 Zr 2 O 12 " may be stabilized at ambient conditions relative to its slightly less conducting tetragonal modification via small amounts of Al 3+ . A simple crystal chemical model is proposed to explain why cubic Al-containing Li 7 La 3 Zr 2 O 12 is (meta)stable at ambient conditions, and why it is such a good ion conductor. -(GEIGER*, C. A.; ALEKSEEV, E.; LAZIC, B.; FISCH, M.; ARMBRUSTER, T.; LANGNER, R.; FECHTELKORD, M.; KIM, N.; PETTKE, T.; WEPPNER, W.; Inorg. Chem. 50 (2011) 3, 1089-1097, http://dx.

Gallium-Doped Li7La3Zr2O12 Garnet-Type Electrolytes with High Lithium-Ion Conductivity

“…showed that LLZO is crystallized with both cubic and tetragonal symmetry, with the cubic phase exhibiting a lithium-ion conductivity two orders of magnitude higher than that for the tetragonal phase 12 Li sites are partially occupied in the LLZO structure. Ta 5+ 14 , Nb 5+ 15 , Te 6+ 16 , and W 6+ 17 that substitute on the Zr 4+ site, as well as Al 3+ 11 and Ga 3+ 18-26 that substitute in the Li sublattice, have been employed to stabilize the cubic phase.…”

Bulk Li mobility enhancement in Spark Plasma Sintered Li(7−3x)AlxLa3Zr2O12 garnet

“…7. In the literature [1,14,15], the two peaks at ~70 ppm and ~82 ppm are attributed to Al 3+ located in the 24d sites and 48g/96h sites in the garnet phase respectively, 48g and 96h being unresolved as they are neighbor sites (see Fig. 1) [10].…”

“…1) [1,6]. Due to partial occupancy of identified Li sites, the diffusion of Li + occurs by a concerted migration mechanism [4,7,8], and the Li content and its distribution among 24d and 48g/96h sites affects the activation energy of the diffusion process [9].…”

“…Site occupancies in the prepared LLAZO were identified using 27 Al and 6 Li MAS NMR [1,[14][15][16]. NMR relaxation time measurements allowed getting Li dynamics parameters, namely the Li mean jump rate and activation energy [11,12].…”

Optimization of Al2O3 and Li3BO3 Content as Sintering Additives of Li7−x La2.95Ca0.05ZrTaO12 at Low Temperature

“…Geiger et al [8] are one of the first groups to note the contamination by Al from the crucible during sintering process and its influence on the stabilizing of the cubic garnet phase. Alternatively, other researches have revealed that the Al acts as a sintering additive by residing in the grain boundaries and also inside of the grain creating more Li-ion vacancies improving the Li-ion conductivity [9][10][11].…”