Formation of anisotropic Tl-1212, Tl-2212, Tl-1223 and Tl-2223 particles using aerosol flow reacted powders

摘要

Highly anisotropic particles of Tl-1212, Tl-2212, Tl-1223 and T1-2223 superconductors were grown. The Tl-free precursor powders with the compositions Ba/sub 1/Ca/sub 2/Cu/sub 3/Ag/sub 0.37/O/sub 6/ and Ba/sub 2/Ca/sub 2/Cu/sub 3/Ag/sub 0.37/O/sub 7/ were prepared using an aerosol flow reactor. These precursor powders were then post-annealed in 0.1 atm oxygen at 700/spl deg/C for 4 h to reduce the carbon present and mixed with Tl/sub 2/O/sub 3/ (typical composition of Tl/sub x/; x=0.6-1.0). The Tl-containing powders were heated, in sealed gold tubes between 650-890/spl deg/C for various times. X-ray diffraction showed that the Tl-2212 and Tl-2223 phases were stable over a wide range of temperatures. Scanning electron microscopy showed evidence for the presence of high aspect-ratio particles. These highly anisotropic particles may of interest for the preparation of powder-in-tube and other powder deposited conductors, for current leads, and for grain alignment studies.