A ONE-DIMENSIONAL CUPRATE CLOSELY-RELATED TO THE 0212-STRUCTURE - ND2BA4CU2O9

The structure of the cuprate Nd2Ba4Cu2O9 has been determined using both X-ray powder diffraction and high resolution electron microscopy. The compound crystallizes in the space group P4̄n 2 with a = 12.072, c = 3.874 Å. The structure consists of isolated chains of corner-sharing CuO5 pyramids whose cohesion is ensured by the presence of Nd3+ and Ba2+ cations, the coordination of which can be described as distorted monocapped trigonal prisms BaO7 and NdO7. A description of the structure in terms of pyramidal copper chains sharing their corners with NdO5 tetragonal pyramids is also given. The resulting three-dimensional framework [Nd2Cu2O8]∞ forms octogonal tunnels where the barium cations and the additional oxygen are located. The close relationships between this one-dimensional cuprate and the layered cuprates are discussed. © 1993 Academic Press, Inc.