Abstract
Superconducting phases of 2212-type, with the general formula Tl 2− x Hg x Sr 2Ca 1Cu 2O z , were synthesized from metal oxides in closed silica tubes at 880°C. The most phase-pure sample was obtained for x=0.7. A mixture with the nominal composition Tl 1.3Hg 0.7Sr 2Ca 1Cu 2O z , used in a single-crystal growth in a high-temperature high-pressure gas trap furnace (HTHP), gave plate-like crystals with a maximum diameter of 500 μm, having unit cell parameters which could be refined to a=3.796 Å and c=28.433 Å (space group I4/ mmm). The structural details were investigated by X-ray single-crystal analysis ( R w=0.025). Both alkaline-earth metal sites in the structure are probably mixed, but with different Ca/Sr ratios. As previously reported, some copper entered the (Tl,Hg) site in the high-pressure synthesis, giving a resulting composition of (Tl 0.8Hg 0.7Cu 0.5)(Sr 1.7Ca 0.3)(Ca 0.7Sr 0.3)Cu 2O 7.5 according to energy dispersive spectrometry (EDS) analysis and structural refinement. T c (onset) for both powder and single-crystal samples, as prepared, was about 45 K, as determined by AC susceptibility.
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