Growth of idiomorphic LiMnPO4 crystals in molten NaCl–KCl and LiF–NaCl–KCl fluxes

Abstract

Olivine-type idiomorphic polyhedral LiMnPO₄ crystals grown from a molten LiF–NaCl–KCl ternary flux at 700 °C are found to be surrounded with well-defined facets of major {100}, {101}, and {210} faces with minor {011} faces. The average size of these crystals of ∼20.7 μm was around ten times larger than those grown from a molten NaCl–KCl binary flux. In situ XRD and TG-DTA measurements revealed that LiMnPO₄ crystals grew from the melt during heating and holding at 700 °C with little assistance from the supersaturation produced by flux evaporation. Time-dependent scanning electron microscopy observation found that Ostwald ripening caused by repeated partial dissolution and reprecipitation of the LiMnPO₄ crystals is the dominant factor in both the development of crystal facets and the mean diameter of individual crystals. The addition of LiF is therefore considered to promote the development of well-defined polyhedral crystals by increasing the solubility of LiMnPO₄ in the molten flux.