文摘
Garnet-type Li5+xLn3MIV2鈥?i>yMVyO12+z (x, y = 0鈥?, z = 0鈥?; Ln = La, Pr, Nd; M = Ta, Zr, Nb) compounds are promising Li-ion conducting solid electrolytes, but their growth manner is still unclear. Herein, the analysis of the low-temperature growth of idiomorphic Li5La3Ta2O12 single crystals as a function of holding temperature and time, cooling rate, flux type, and solute concentration revealed a unique growth manner. Li5La3Ta2O12 crystals were grown at 500 掳C from LiOH flux and transformed into Li7La3Ta2O13 at 700 掳C. The pseudo-perovskite-type LiLa2TaO6 phase, initially formed during the holding at 500 掳C, was efficiently transformed into the Li5La3Ta2O12 phase with increasing holding time. The growth of Li5La3Ta2O12 single crystals was independent of the cooling rate but was affected by the kind of flux and solute concentration. A low solute concentration (1 or 5 mol %) was the key to obtain well-dispersed and idiomorphic single crystals. The optimum growth conditions involved a holding temperature of 500 掳C, a solute concentration of 1 or 5 mol %, and a holding time of 10 h. These findings indicate that formation and growth of Li5La3Ta2O12 single crystals are not only controlled by a general flux growth process but also involve chemical reactions between solutes and LiOH flux. Finally, high-resolution transmission electron microscopy image and selected area diffraction pattern highlighted products with high crystallinity and well-developed {110} and {211} facets.