Commensurate variant of the A14Cu24O41-type structure of a new (Nd,Y,Sr,Ca)14(Cu,Ca,Sr)24O41 compound

A new A14Cu24O41-type phase of the composition (Nd3.66Y1.34Ca6.5Sr2.5) (Cu23.15Ca0.425Sr0.425)O41 has been obtained by spontaneous crystallization from flux. The structure consisting of two sublattices incommensurate in one direction is determined and refined by single-crystal x-ray analysis (692 crystallographically nonequivalent reflections) in the commensurate approximation up to R=0.0512. The parameters of the averaged unit cell are a=12.515(2) A, b=11.294(6) A, and c=27.544(8) A =7c'=10c'', where c'=3.936(1) A and c''=2.7537(4) A are the parameters of two incommensurate sublattices, sp. gr. Abmm. The incommensurability factor q=0.6996(6) provided the consideration of the structure as a commensurate one within the accuracy of determining the translation parameters. The structure determined differs from the known A14Cu24O41-type structures by the mutual arrangement of the structural units ([CuO2]-ribbons) in one of the sublattices, which is explained by the presence of Nd-atoms in the other sublattice. The partial substitution of Cu by Ca and Sr atoms never observed for such structures earlier is established. The almost complete incommensurability observed is interpreted in terms of the interaction between the two sublattices forming cation-oxygen bonds