THE 1ST SUPERCONDUCTING THIN-FILM OXYCARBONATES - COHERENT INTERGROWTH OF SEVERAL MEMBERS OF A NEW STRUCTURAL SERIES (CACUO2)M(BA2CUO2CO3)N

Superconducting thin films of copper oxycarbonates have been synthesized for the first time using laser ablation. The resistance measurements show a broad transition with T(c onset) ranging from 80 to 100 K and zero resistance below 60 K. Magnetic measurements indicate diamagnetism below 58 K in the best film. The ED and HREM studies show that these new oxycarbonates are tetragonal with a almost-equal-to a(p) and c almost-equal-to (m + 2) x a(p), and that the films consist of an intergrowth of several members of a family with the general composition (CaCuO2)m(Ba2CuO2CO3)n. The main member that forms the matrix, Ba2Ca3Cu4CO3O8 (m = 3; n = 1), consists of double layers of CuO4 groups sandwiched by pyramidal copper layers and interconnected with layers of CO3 groups. In a general way, the different members of the series can be described as the intercalation of layers of carbonate groups in the infinite-layer structure CaCuO2. The origin of superconductivity and the relationships with bulk ''BaCaCu'' oxycarbonates that are prepared at high pressure are discussed.