A new layered cuprate structure-type.

Phases crystalizing in a new structure-type with general formula (A sub (1-x) A' sub x) 14 Cu sub (24) O sub (41) (A = alkaline earth metal, A' = trivalent metal) with an extended stoichiometry range have been found in studies of the Sr-Y-Cu-O, Ba-Sr-Cu- O, Ca-Sr-Bi-Cu-O and Ca-La-Cu-O systems. Single crystal X- ray studies on several crystals grown from different alkaline earth/metal oxide-cuprate melts reveal a common orthorhombic F-centered subcell of a=11.3A, b=13.0A and c=3.9A. Superstructure is observed in some crystals, leading to a 7-fold increase of the c-axis. As in Ba sub 2 YCu sub 3 O sub 7, the Cu atoms are found as Cu-O planes and linear Cu-O chains. Due to shear in the planes, half of the Cu-O squares share edges, producing Cu-Cu zigzag chains, similar to the planes observed in CaCu sub 2 O sub 3. In the linear Cu-O chains, the Cu-O squares share edges as well, leading to a short Cu-Cu contact of 2. 75A. Experiments on ceramic samples indicate that the oxygen content is fixed and that the samples are semiconducting.