Abstract
The ternary oxide EuBa 2Cu 3O χ has been studied as a function of oxygen content using thermopiezic analysis, X-ray diffraction and scanning electron microscopy. The same measurements, in addition to 57Fe Mössbauer spectroscopy and EXAFS, have been carried out on samples where 1 or 2% of the copper is replaced by iron. The orthorhombic-tetragonal transition occurs on heating to 500°C in vacuum when χ=6.6. There is little change in the ceramic microstructure prior to the onset of vitrification at about 900°C. Mössbauer spectra are consistently fitted using four quadrupole doublets in the orthorhombic phase and two doublets in the tetragonal phase. The assignments of these doublets to iron in different oxidation states on Cu1 and Cu2 sites is based on EXAFS data and on the Mössbauer hyperfine splitting. Iron has a strong preference of Cu1 sites and the data suggest an Fe 4+ charge state. Iron on Cu2 sites is Fe 3+.
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