We have synthesized compounds which may be viewed as stacking of pairs of CuO2 layers alternating with RuO2 layers. There are two structural variants, RuSr2GdCu2O8-delta and RuSr2Gd1+xC epsilon(1-x)Cu(2)O(10-delta), which are denoted shortly 1212 and 1222 structures. In their stacking sequence, they differ solely by the sheets separating the CuO2 bilayers. The synthesis of these phases is accompanied by the formation of small amounts of SrRuO3 impurities, which appear to have a much more devastating effect on the superconducting properties of the 1212 phase as compared to the 1222 phase. We present and investigation of the influence of various synthesis procedures on the appearance of impurity phases and on superconductivity in the 1212 system.
