STRUCTURE AND MOSSBAUER-STUDY OF THE DOUBLE PEROVSKITE BA2INCU1-XFEXO4+Y (X=0.5)

The substitution of Fe for Cu stabilizes the structure of Ba2InCuO4+y and an order-to-disorder structural transformation is observed upon va rying the preparation conditions. This variation occurs either by heat ing the ordered phase at higher temperature in air or by heating it in Ar atmosphere during thermogravimetry experiments. Mossbauer spectros copy revealed that, for the ordered sample, Fe is probably in a ''dist orted'' tetrahedral coordination and shares with Cu the middle plane. In the disordered sample, due to cation disorder, there are two more s ites: one corresponding to Fe3+ and one to Fe4+. The picture that emer ges from the Mossbauer data mimics the observed behavior of iron-subst ituted Cu(1) sites of the 123 compound. (C) 1997 Elsevier Science Ltd.