The Yin and Yang of Crystal Growth of Ternary Lanthanide Fluorides Na 3 x Ln (2-x) F 6 ( Ln = Er–Yb)

The mild hydrothermal method using sodium carbonate in the presence of HF(aq) resulted in a series of high-quality single crystals of Na3xLn(2-x)F6 (Ln = Er–Lu). Sodium carbonate was found to strongly promote the formation and crystallization of the Na3xLn(2-x)F6 phase under hydrothermal conditions. Structure determination was carried out by single-crystal X-ray diffraction. All four phases are isostructural and crystallize in the hexagonal space group P-6. Pure polycrystalline powders of Na3xLn(2-x)F6 (Ln = Er–Lu) were obtained via flux synthesis using NaNO3/NaF as the flux.