Synthesis, characterisation and crystal chemistry of Pb₃Sr₃Cu₃O₈Br: a new layered Copper Oxide-Bromide

A new layered copper oxide-bromide, with the formula Pb3Sr3Cu3O8Br, has been synthesised. The crystal structure of this compound is isostructural with that of Pb3Sr3Cu3O8Cl and is closely related to that of the high temperature superconductor Pb2Sr2Y1-xCaxCu3O8. Although Pb3Sr3Cu3O8Br possesses infinite CuO2 sheets, considered a prerequisite for high temperature superconductivity, it has not proved possible to induce superconductivity in this compound by oxygen annealing or methods of chemical substitution. Annealing Pb3Sr3Cu3O8Br under flowing oxygen gas leads to the absorption of 1.5 additional oxygen atoms per formula unit, accompanied by a change in the unit-cell symmetry from C-centred to primitive orthorhombic. We have found that a solid solution exists in the Pb3Sr3Cu3O8Br1-xClx system, bounded by the end members Pb3Sr3Cu3O8Br and Pb3Sr3Cu3O8Cl. High temperature X-ray diffraction studies of Pb3Sr3Cu3O8Br, under flowing nitrogen gas, indicate that this material remains orthorhombic below a temperature of 800degreesC; prolonged dwelling at this temperature induces partial sample decomposition. (C) 2002 Elsevier Science B.V. All rights reserved.