Environmentally Friendly Flux Growth of High-Quality, Idiomorphic Li₅La₃Nb₂O₁₂ Crystals

Abstract

High-quality, idiomorphic, single-phase Li5La3Nb2O12 crystals were successfully grown using a LiOH flux cooling method at the relatively low temperature of 500 °C at a solute concentration of 5 mol %. The grown Li5La3Nb2O12 crystals had polyhedral shapes with well-developed, flat {211} and {110} faces. Their shapes were relatively uniform, and the average crystal size was approximately 59.2 μm. No aggregation was observed in scanning electron microscopy images. The high crystallinity of the Li5La3Nb2O12 crystals was confirmed by transmission electron microscopy images. Their lattice parameter was determined from the X-ray diffraction pattern to be a = 1.281 nm, which is consistent with the literature value (a = 1.282 nm). Furthermore, the crystal phase, form, size, and crystallinity of the flux-grown Li5La3Nb2O12 crystals were obviously dependent on the growth conditions including the solute concentration and holding temperature.

Thin and Dense Solid-solid Heterojunction Formation Promoted by Crystal Growth in Flux on a Substrate

“…It indicates that the tilted grain boundary represented by the Σ3 (2–1–1) = (1–21) models is one of the most stable grain boundaries in the Li 5 La 3 Nb 2 O 12 system. This computationally predicted trend is consistent with the thermodynamically stable faces of the Li 5 La 3 Nb 2 O 12 crystals grown from a molten LiOH flux 25 .

Figure 6Trajectories of the Li, La, Nb, and O framework atoms obtained for Σ3 (2–1–1) = (1–21) at a temperature of 1300 K.

Figure 7RDFs for the Li, La, Nb, and O interactions in the bulk (black) and at the tilted grain boundary Σ3 (2–1–1) = (1–21) model (red): ( a ) Li-Li, ( b ) La-La, ( c ) Nb-Nb, ( d ) O-O, ( e ) La-Li, ( f ) Nb-Li, ( g ) O-Li, (h) Li-O, ( i ) La-O, and ( j ) Nb-O.

Figure 8( a ) Arrhenius plots of the Li +  conductivity calculated for isotropic 3D Li diffusion path in the bulk garnet Li 5 La 3 Nb 2 O 12 along the a , b , and c axes. ( b ) Fitted Li +  conductivity at 300 K derived from the MSD analysis.

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“…The face angle analysis suggests that the crystal surface was dominantly surrounded by larger {211} and smaller {110} faces. Such crystallographic features dovetail with those of Li 5 La 3 Nb 2 O 12 single crystals that were homogeneously grown from LiOH flux (with LiOH·H 2 O, La 2 O 3 , and Nb 2 O 5 powders reacting in a crucible) 25 .

Figure 3Time-dependent SEM images of the Nb substrate during reaction in a molten LiOH flux with La 2 O 3 at 500 °C in air: ( a ) as-purchased Nb substrate, after ( b ) 10 min, ( c ) 60 min, and ( d ) 600 min.

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“…We have reported the Li + conductivity of the sinter bodies prepared from the Li 5 La 3 Nb 2 O 12 crystals of which it was grown from LiOH flux under same recipe described in this paper 25 . The Li + conductivity was of 5 × 10 −6  S·cm −1 at room temperature, as evaluated by conventional electrochemical impedance spectroscopy.…”

“…We applied similar recipe of the flux growth of polyhedral shaped Li 5 La 3 Nb 2 O 12 single crystals the crystal layer formation 25 . La 2 O 3 (0.305 g) and LiOH·H 2 O (0.295 g) were mixed in an alumina crucible 30 mL in volume for 30 min.…”

Low-temperature growth of idiomorphic cubic-phase Li7La3Zr2O12crystals using LiOH flux

“…Here, we propose a one-step synthetic route to prepare cubic-phase LLZ using LiOH-based flux growth. The flux method, which is conventionally used for crystal growth from the liquid phase, can possibly provide a growth temperature that is lower than the melting points of the solutes [25][26][27][28][29][30] (ref. 28) has been demonstrated in our previous studies.…”