57Fe Mossbauer investigation of the substitutional effect of praseodymium in 1-2-3 compounds

Fe-57 Mossbauer spectroscopy measurements were performed on the perovskite compounds Eu0.7Pr0.3Ba2((Cu0.99Fe0.01)-Fe-57)O-3(7-delta) EuBa1.5Pr0.5((Cu0.99Fe0.01)-Fe-57)(3)O7-delta and EuBa1.3Pr0.7((Cu0.99Fe0.01)-Fe-57)(3)O7-delta.The observed Fe-57 Mossbauer spectra provided an evidence for the correct site assignment of subspectra originating from Fe-57 in different microenvironments. Apart from a minor component which was assigned to the Fe-57 in the Cu(2) site of the copper oxide plane, all the subspectra could be attributed to the Fe-57 in the Cu(II) copper oxide chain site with a fourfold (doublet D1), fivefold (doublet D2) or sixfold (doublet D3) oxygen coordination. In contrast, in the compound EuBa2((Cu0.99Fe0.01)-Fe-57)(3)O7-delta the 6-coordinated (D3) species has not been observed. The substitution of Pr for Eu or for Ba resulted in an increased occupancy of the O(5) antichain oxygen sites, which was explained by the charge neutrality criterion. Especially, the replacement of Ba2+ with Pr3+ led to an unusually high degree of occupancy of O(5) sites. In the Fe-57 Mossbauer spectra the relative area of the 6-coordinated species (D3) increased, and that of the 4-coordinated one (D1) vanished completely in the case when Pr was substituted for Ba. Furthermore, the proportion of the 6-coordinated (D3) species increased at the expense of the 5-coordinated (D2) one with an increasing concentration of Pr at the Ba site. These experimental results are consistent with the variety of Mossbauer results reported so far.