Synthesis of Needle-shaped Rare Earth Oxide by Solvothermal Treatment of Rare Earth Chloride

The reaction of rare earth (RE) chloride hydrates (Y, Er and Yb) in 1,4-butanediol (1,4-BG) at 300 oC for 2 h gave mixtures of RE(OH)2Cl and RE2O3•xH2O, and the products were composed of irregularly-shaped particles. The prolonged reaction (10 h) also yielded a mixture of RE(OH)2Cl and RE2O3•xH2O for Er or Y, but phase-pure RE2O3•xH2O was obtained for Yb. The latter product was comprised of needle-shaped single crystals with 0.2– 0.6 μm width and 5–15 μm length. The reaction in toluene at 300 oC for 2 h yielded phasepure Yb2O3•xH2O and SEM image of the product showed the formation of irregularly-shaped particles. By the prolonged reaction time (6 h), the morphology of Yb2O3•xH2O changed, and needle-shaped single crystals with 80–190 nm width and 0.5–1.0 μm length were obtained, which were much smaller than those obtained in 1,4-BG. The Yb2O3•xH2O phase decomposed to Yb2O3 at 350–500 oC, preserving the needle-shaped morphology, which was maintained even after calcination at 800 oC. Single crystals of Yb2O3 obtained by calcination of Yb2O3•xH2O at 500 oC had very small voids and the voids were enlarged to 35 Å in diameter by calcination at 800 oC.