IRON MIGRATION IN THE (Y,CA)BA2(CU,FE)O6+DELTA SYSTEM

Mossbauer spectroscopy of Fe-57 in Y1-xCaxBa2Cu3-xFexO6+y for x = 0.09 was used to study the site distribution of Fe in oxygen-rich and oxyg en-reduced samples. In the superconducting sample (y = 1), (T(c) = 85 K) more than 90% of the Fe resides in the Cu(1) site. For y = 0 the Cu (2) site orders magnetically at T(N) = 425 K. Based on the typical beh avior of Fe in the magnetic Cu(2) site, we find that about 80% of the Fe occupies this site, thus we prove migration of Fe from Cu(1) to Cu( 2) sites during depletion of oxygen at elevated temperatures. The spec trum above T(N) is smeared because of a distribution in the quadrupole interactions.