Europium oxidation state and local structure in silicate glasses

摘要: Europium L III-edge XAS spectra were recorded for silicate glasses of different compositions, quenched from melts equilibrated at oxygen fugacity ( f O2). The Eu XANES vary systematically with glass composition and O2 (−log ~0 to ~11.9) indicating changes in the oxidation state. intensity main peaks on absorption edges quantified used determine Eu2+/(Eu2++Eu3+) ratio. All Eu-bearing synthesized air show prevalent presence Eu3+ but also, unexpectedly, a small amount Eu2+ basaltic up 20% haplogranitic sample. Moreover, analyses samples reducing conditions (from FMQ IW-2) that europium is always more reduced than glasses. No relationship has been found between valence alkali content studied structural environment was determined by EXAFS analyses, demonstrating behavior as function O2. In fact, air, both bonded six O atoms regular octahedron (CN = [6 ± 0.5]) similar distances about 2.30 0.02 A. On other hand, almost purely divalent have higher coordination [9 1]) longer (2.68 A). This work clearly demonstrates that, addition fugacity, melt also plays strong role affecting first time, experimentally derived data geological interest are presented.