Synthesis of Mesoporous Needle‐Shaped Ytterbium Oxide Crystals by Solvothermal Treatment of Ytterbium Chloride

The reaction of rare‐earth (RE; Y, Er, and Yb) chloride hydrates in 1,4‐butanediol at 300°C for 2 h gave mixtures of RE(OH) 2 Cl and RE 2 O 3 · x H 2 O, and the products were composed of irregularly shaped particles. A prolonged reaction (10 h) yielded a mixture of RE(OH) 2 Cl and RE 2 O 3 · x H 2 O for Er or Y, but phase‐pure RE 2 O 3 · x H 2 O was obtained for Yb. The product for Yb comprised needle‐shaped single crystals of Yb 2 O 3 · x H 2 O with a width of 0.2–0.6 μm and a length of 5–15 μm. The Yb 2 O 3 · x H 2 O phase decomposed to Yb 2 O 3 at 350°–500°C, preserving the needle‐shaped morphology; this was maintained even after calcination at 1100°C. Single crystals of Yb 2 O 3 obtained by the calcination of Yb 2 O 3 · x H 2 O at 500°C had very small voids and the voids were enlarged to 35 Å in diameter by calcination at 800°C.