We measured XAFS spectra of trace amount of ytterbium (Yb) incorporated in calcite, a stable phase of calcium carbonate. Calcium carbonate was precipitated from a mixed solution of CaCl2 aq and NaHCO3 aq with a given amount of YbCl3. Concentrations of Yb were 5 μmol kg -1 in the starting solutions and Yb/Ca molar ratio in the precipitated calcium carbonate was 1.2 × 10-3. Ytterbium L III-edge XAFS spectra were collected in the fluorescence mode at the beamline BL-12C of the KEK-PF. Analysis of the XAFS results indicated, (1) Approximately 15% Yb ion existed as divalent ions in the calcite. (2) Yb 3+, major Yb species in the calcite, is located at the Ca 2+ site in the calcite. The local structure around Yb3+ is significantly different from that of Ca2+. The coordination number of Ca2+ in the crystal structure of calcite is 6 and Ca-O distance is 2.36?Å. In contrast, the nearest Yb-O coordination for Yb-doped calcite is split into two shells, the nearest 4 oxygen atoms and the second nearest 2 oxygen atoms, and their Yb-O distances are 2.24?Å and 2.77?Å, respectively. It was shown that localized structural relaxation occurred around Yb3+ which has smaller ionic radius than Ca2+.
|ジャーナル||Physica Scripta T|
|出版ステータス||出版済み - 2005|
|イベント||12th X-ray Absorption Fine Structure International Conference, XAFS12 - Malmo, スウェーデン|
継続期間: 6 23 2003 → 6 27 2003
All Science Journal Classification (ASJC) codes