Flux-Mediated Topochemical Growth of Platelet-Shaped Perovskite LiNbO₃ Single Crystals from Layered Potassium Niobate Crystals

Well-defined, platelet-shaped LiNbO₃ single crystals were prepared by a flux-mediated topochemical reaction from platelet K₄Nb₆O₁₇ crystals with a mixture of LiNO₃ solute and alkali metal nitrate (LiNO₃, NaNO₃, and KNO₃) fluxes at 600 °C. Crystallographic structural characterizations revealed that the LiNbO₃ crystals inherited the K₄Nb₆O₁₇ crystal shape with well-developed {012} faces. The topochemical reaction in molten KNO₃ promoted smooth surface formation, in contrast to LiNO₃ and NaNO₃, which formed rough surfaces. We further found that the dissolution and deposition reaction occurs repeatedly in the vicinity of the LiNbO₃ crystal and KNO₃ flux interface. It is considered that the KNO₃ flux hybridized with the LiNO₃ solute provides a moderate solubility and dissolution rate suitable for crystal growth. We also achieved reed-shaped LiNbO₃ crystal growth by applying the same technique to the KNb₃O₈ crystal template.