We report here on X-ray absorption fine structure (XAFS) measurements used to determine the structure of the Yb3+ ion in aqueous solutions over a range of temperatures from 25 to 500 ??C and pressures up to 270 MPa. Fluorescence Yb L3-edge spectra were collected separately from nitrate (0.006m Yb/0.16m HNO3) and chloride (0.006 m YbCl3/0.017 m HCl) aqueous solutions within a hydrothermal diamond anvil cell. The Yb-O distance of the Yb3+ aquo ion in the nitrate solution exhibits a uniform reduction at a rate of 0.02 A??/100 ??C, whereas the number of oxygens decreases from 8.3 ?? 0.6 to 4.8 ?? 0.7, in going from 25 to 500 ??C. No evidence for nitrate complexes was found from measurements made on this solution. The Yb3+ is found to persist as an aquo ion up to 150 ??C in the chloride aqueous solution. In the 300-500 ??C range, chloro complexes are found to occur in the solution, most likely of the type Yb(H2O)??-nCln+3-n (?? ??? 7). The Yb-Cl distance of the chloro ytterbium(III) complexes is found to decrease uniformly at a rate of about 0.02 A??/100 ??C, whereas the number of chlorines increases from 0.5 ?? 0.3 to 1.8 ?? 0.2 in the 300-500 ??C temperature range. Conversely, the Yb-O distance undergoes a lower uniform reduction at a rate of 0.007 A??/100 ??C, whereas the number of oxygens decreases from 8.3 ?? 0.5 to 5.1 ?? 0.3 in going from 25 to 500 ??C in the same solution.
Additional Publication Details
The structure of Yb3+ aquo ion and chloro complexes in aqueous solutions at up to 500 ??C and 270 MPa