Oxygen stoichiometry in BaRE(Cu0.5Fe0.5)(2)O5+delta compounds with perovskite or double perovskite structure

The oxygen stoichiometry variation in the BaRE(Cu0.5Fe0.5)(2)O5+delta serie s is established with rare earth elements having ionic radii (CN = 8) in th e range of 0.977-1.160 Angstrom (Lu-La). The double-perovskite structure is stable with RE = Lu-Pr, while La prefers the simple-perovskite structure. In the double-perovskite structures with RE = Lu-Sm the oxygen content was found to be constant (delta approximate to 0) against normal-pressure oxida tive and reductive heat treatments, whereas a larger rare earth ion, i.e. N d or Pr, allows continuous oxygen content tuning within about 0.23 and 0.32 oxygen atoms, respectively. In the La perovskite the oxygen content could be varied from delta approximate to 0 to 0.45. The Fe-57 Mossbauer spectros copy measurements revealed that the transition temperature of magnetic orde ring decreased with an increase in the oxygen content for both the double- and simple-perovskite structures.