Synthesis and processing of Bi-doped Hg₁Ba₂Ca₂Cu₃O_y superconductors

The sequence of reactions that occur during the synthesis of (Hg, Bi)Ba₂Ca₂Cu₃O_y, (HgBi1223) was studied using a series of quenching experiments. The formation and decomposition of the intermediate phases during the high temperature reaction were followed as a function of temperature. Heat treatment conditions were optimized for the synthesis of pure HgBi1223 phase using commercial BaCaCuO precursor powders. An additional lower temperature annealing stage after high temperature reaction is shown to improve the micro structural characteristics of HgBi1223 samples. Control of Hg-pressure is shown to be crucial for achieving grain growth and texture in the final products. A novel approach for the control of Hg-pressure during the synthesis of HgBi1223, which consists of using CaHgO₂ as an 'external Hg-source', is demonstrated. Samples synthesized using the new synthesis protocol exhibit improved micro structural and magnetization properties.