Morphology and structure of rare earth borate (REBO₃) synthesized by glycothermal reaction

The glycothermal reaction of the rare earth (RE) acetates with trimethoxyborane (RE/B = 1) at 315 °C for 2 h yielded REBO₃ for Tm, Yb and Y. For Gd–Er, REBO₃ was contaminated with amorphous products. Mixtures of RE(OAc)O, REBO₃ and amorphous products were obtained for Sm and Eu, while only RE(OAc)₂(OH) was obtained for La. The space group of the REBO₃ crystal obtained from Sm–Er and Y was P6₃/m, and mixture of REBO₃ crystals with P6₃/m and R \( \ifmmode\expandafter\bar\else\expandafter\=\fi{3} \) c were obtained for Tm and Yb. Prolonged reaction time (6 h) yielded REBO₃ without contamination of the amorphous product or RE(OAc)O for Eu–Yb and Y. For the reaction of yttrium acetate and trimethoxyborane with Y/B ratio of 1/3–3/1 for 2 h, YBO₃ was only the binary oxide detected. The YBO₃ particles were spheroidal with a diameter of 1 μm. The selected area electron diffraction of a whole particle indicated that the each particle is a “single crystal” of YBO₃ grown from one nucleus.