151Eu Moessbauer spectroscopy studies of substituted EuBa2Cu3O7 systems

Moessbauer spectroscopy studies of 151Eu in EuBa2Cu3O7, EuBa2Cu3O6, EuBa2Cu3O6S, EuBaKCu3O7, EuBa2Cu2.5Fe0.5O7, Eu0.5Pr0.5Ba2Cu3O7, Eu1.25Ba1.75Cu3O7 and EuCaBaCu3O7 at several temperatures have been performed. The major conclusions are: All substitutions affect the Eu quadrupole interation (10-20%). Substitution of 0 by S increases the Eu quadrupole interaction by 15% and increases η from 0.3 to 0.8 which proves that S substitutes oxygen in the immediate neighbourhood of the rare earth ions. In EuCaBaCu3O7 the quadrupole interaction is larger by 80% than in EuBa2Cu3O7, proving that in this structure Eu occupies predominantly the Ba sites. (orig.)