A CR-SUBSTITUTED 1201-SUPERCONDUCTOR - TL-0.8(CRO4)(0.2)BA2CUO4.2-DELTA

A thallium and barium based superconductor, Tl-0.8(CrO4)(0.2)Ba2CuO4.2 -delta with a T-c of 42 K, has been stabilized by partially substituti ng chromium for thallium. The structure of this new oxychromate has be en characterized using electron diffraction, EDS, high-resolution elec tron microscopy, infrared spectroscopy and X-ray diffraction. It exhib its a ?1201-type structure with a P-type lattice and the parameters of the average tetragonal cell are a = 3.8873(1) Angstrom and c = 9.3435 (4) Angstrom. The presence of chromate groups has been shown from IR. They are located within the intermediate layer of the '1201' structure , Cr sitting in the Tl sites, The HREM investigation evidences the exi stence of short range ordering between thallium and chromate groups. T he ordering mode is compared with that adapted by the '1201' strontium based oxychromate Tl-3(CrO4)Sr8Cu4O16. (C) 1997 Elsevier Science B.V.