SYNTHESIS OF HG-RE-BA-CA-CU-O SUPERCONDUCTORS BY A 2-STEP METHOD

A new two-step method has been developed to synthesize (Hg,Re)Ba2Ca2Cu 3Oy with lower annealing temperatures as compared to conventional meth ods using a precursor which contains the (Hg,Re)Ba2CaCu2Oy phase. In t he first step, high phase purity (Hg,Re)Ba2CaCu2Oy superconductors are prepared from commercially available Ba2CaCu2OX precursors, HgO, and Re2O7. In the second step, the finely ground (Hg,Re)Ba2CaCu2Oy is mixe d with Ca-Cu-O and HgO. This precursor mix is encapsulated in evacuate d quartz tubes and annealed for 8 to 48 h between 750 degrees C and 85 0 degrees C. The resulting samples have (Hg,Re)Ba2Ca2Cu3Oy as a majori ty phase and exhibit a critical temperature of 133 K as prepared. The superconducting grains are platelike and randomly oriented. The grain sizes depend on the annealing time and temperature and reaches up to 3 0 mu m diameter and 5 mu m thickness. Second phases are mainly unreact ed Ba2CaCu2Ox and Ca-Hg-O.