A NOVEL BISMUTH CUPRATE, BI14+XSR7BA7CU7-XO42+X/2, 7TH MEMBER OF A STRUCTURAL SERIES, (BI2A2CUO6)N-2 (BI4+XA4CU2-XO12+X/2), RELATED TO THE 2201 BISMUTH CUPRATES

A new bismuth based cuprate has been synthesized with composition Bi15Sr7Ba7Cu6O42.5. It crystallizes in a monoclinic cell with a = 20.121 (5) Å, b = 5.509 (1) Å, c = 25.736 (10) Å, β = 111°08 (2), and the possible space groups are A2, Am and A2/m. A high resolution electron microscopy study showed that its structure results in a periodic rupture of infinite layers similar to those observed in the “2201” modulated superconducting oxide; it involves a sharing mechanism along c forming 2201-type ribbons seven polyhedra wide. A new family of oxides, the “collapsed” 2201-type bismuth cuprates, is described, (Bi2A2CuO6)n-2 (Bi4+xA4Cu2-xO12+x/2), this oxide being the n = 7 member. The existence of defective member n′ = 6 has been shown, which sometimes results in regular local intergrowth [6/7]. The close structural relationships with the 2201 modulated phase is illustrated by the easy junction between the two structures. No superconducting behavior has been detected. © 1993 Academic Press, Inc.