Synthesis and thermal reactions of rhabdophane-(Yb or Lu)

Poorly crystalline rhabdophane-(Yb or Lu) was synthesized by precipitation from mixed aqueous solutions of Ln(NO3)3 (Ln = Yb or Lu), (NH4)2HPO4, and citric acid with the mixing mole ratios of (NH4)2HPO4/Ln(NO3)3 = 4 and citric acid/Ln(NO3)3 = 5 to 30, at pH 7 and 90°C for 7 to 30 days. However, unknown XRD peaks and C–O bond FTIR absorption peaks were observed for the precipitates. These peaks disappeared with increasing heating temperature up to 400°C in air, and single phase rhabdophane-(Yb or Lu) was obtained when heated at 400 to 800°C in air. Chemical formulas of the single phase rhabdophane were YbPO4·0.4H2O and LuPO4·0.5H2O, respectively. The water corresponding to 0.4H2O (or 0.5H2O) was zeolitic water. The lattice constants are a = 0.676 and c = 0.626 nm for Yb, and a = 0.674 and c = 0.630 nm for Lu. Rhabdophane-(Yb or Lu) changed into the xenotime structure above 860°C, which was stable even at 1800°C in air.