Hydrothermal synthesis of LnMnO₃ (Ln = Ho-Lu and Y): Exploiting amphoterism in late rare-earth oxides

The reactivity of Mn₂O₃ and late rare-earth sesquioxides in alkaline aqueous solution affords a high-yield formation of rare-earth manganites, LnMnO₃ (Ln = Ho-Lu and Y). The yield of the products depends significantly on the pH, which determines the solubility of the manganese cation, and reaction temperature, which regulates the decomposition of the insoluble rare-earth trihydroxide, Ln(OH)₃, to the more reactive oxide hydroxide, LnO(OH). Plate- and needle-like LnMnO₃ crystallites of a few micrometers in size have been prepared at reaction temperatures where the rare-earth oxide hydroxide is thermodynamically stable, whereas at lower temperatures the insoluble rare-earth trihydroxide persists and no reaction is observed.