Synthesis of(Hg,Re)Ba2Can-1CunOy superconductors

High phase purity (Hg,Re)Ba2Ca1Cu2Oy and (Hg,Re)Ba2Ca2Cu3Oy superconductors were prepared from commercially available Ba2Can-1CunOx precursors, HgO, and Re2O7. The addition of Re was found to have beneficial effects on the phase formation and chemical stability of the superconducting materials. Optimal annealing temperatures were found to be above 880 degrees C for the (Hg,Re)Ba2Ca2Cu3Oy phase and below 850 degrees C for the (Hg,Re)Ba2Ca1Cu2Oy phase. The microstructure of the samples is dominated by high density island-like superconducting areas interconnected by low density superconducting material and second phases. The randomly oriented platelike superconducting grains are typically around 5 mu m thick and up to 100 mu m long. Investigations of (Hg,Re)Ba2Ca2Cu3Oy samples quenched from various annealing stages indicate that the (Hg,Re)Ba2Ca2Cu3Oy phase forms via the (Hg,Re)Ba2Ca1Cu2Oy phase and is assisted by a liquid phase on a microscopic length scale.