RBA2CU2FEO7 PHASES (R = Y, EU) - SYNTHESIS, STRUCTURE, AND MOSSBAUER-SPECTRA

The reaction of Y/Eu, Cu, Fe oxides and Ba carbonate in a ratio of 1:2 :1:2 at 980 degrees C in an oxygen current forms double-phase systems; in each system, the major phase is a 123 type orthorhombic three-laye red structure, and the secondary phase, amounting to about one-third o f the major phase, is a tetragonal, nearly pseudocubic 123 structure. Both phases in the yttrium and europium systems are characterized by f ormation of weak superstructures with doubled parameters of the ordina ry three-layered cell. In each system, the two phases seem to differ i n the content and distribution of iron. Based on the gamma resonance d ata, it is concluded that similar to 2/3 of iron atoms occupy Cu(2) po sitions in the form of Fe3+ and are magnetically ordered at room tempe rature. The other Fe atoms occupy Cu(1) positions with different coord inations; some of the octahedrally coordinated Fe3+ ions in Cu(1) posi tions (major part in the case of the Eu system) are magnetically order ed, probably, under the influence of magnetic ordering in Cu(2) sublat tices containing Fe3+ ions.