ORDERED SUBSTITUTION OF CO3 GROUPS FOR CUO4 SQUARE GROUPS IN THE 123 STRUCTURE - THE OXYCARBONATE Y4SR8CU11CO3O25, N=4 MEMBER OF THE SERIES YNSR2NCU3N-1CO3O7N-3

The structure of a new Sr-based related 123 oxide is characterized by ED and HREM. The Y4Sr8Cu11CO3O25 microphase corresponds to the ordered replacement of CO3 groups for CuO4 square groups of the 123 structure, leading to the ''4a x b x 2c'' B-centered supercell. It can also be described in terms of nth=4th member of the YnSr2nCu3n-1CO3O7n-3 series. In spite of the absence of superconductivity for this phase, the compounds of this series may be considered as potential superconductors, taking into consideration the possible substitution of calcium for yttrium.