TLBA2(EU, CE)2CU2O9+DELTA, A NEW MEMBER OF THE DOUBLE FLUORITE-TYPE CUPRATE FAMILY - STRUCTURE AND POSSIBLE INDUCED SUPERCONDUCTIVITY BY OXYGEN HIGH-PRESSURE ANNEALING

We report here the synthesis of a "1222"-type compound oxide TlBa2(Eu1.5Ce0.5)Cu2O9+delta whose structure has been characterized by the combination of X-ray powder diffraction (XRD) and electron diffraction. The material has a tetragonal crystal structure (14/mmm space group) and lattice constants a = 3.8784(5) angstrom and c = 30.415(5) angstrom. The structure of this compound consists of an intergrowth of three types of layers: pyramidal copper layers (oxygen-deficient perovskite), double fluorite-type layers, and double rock salt layers. An as-synthesized sample of this material has a superconducting transition temperature, T(c), of 25.5 K and a superconducting volume fraction at 5 K of 0.3%. Both T(c) and superconducting volume fraction were increased (up to 40 K and 5% (at 5K), respectively) when the sample was annealed at a pressure of 100 bar of oxygen at 500-degrees-C for 10 h. We believe that this new 1222-type material of TlBa2(Eu1.5Ce0.5)Cu2O9+delta is still in the underdoped region. If one can apply even higher oxygen pressures in the annealing process, a higher T(c) and superconducting volume fraction may be possible.