Synthesis and stability of HgRe1212 and HgRe1223 superconductors

Synthesis, phase stability, and superconducting properties of Re-doped Hg1212 and 1223 superconductors are reported. HgRe1212 and HgRe1223 were synthesized using a common synthesis protocol, using commercial BaCaCuO precursor powders with CaHgO/sub 2/ as the external Hg-source. Both starting composition and reaction temperature affect the phase stability and microstructure of the final product. The resulting superconducting phase in both Hg/sub 0.8/Re/sub 0.2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub y/ and Hg/sub 0.8/Re/sub 0.2/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub y/ compositions was either HgRe1212 or HgRe1223, depending on the reaction temperature. The microstructure and superconducting properties of HgRe1212 and HgRe1223 samples, however, depended to a large extent on the starting composition. Both the HgRe1212 and HgRe1223 samples synthesized from a nominal composition of Hg/sub 0.8/Re/sub 0.2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub y/ had larger and aligned colonies of grains whereas the samples synthesized a nominal composition Hg/sub 0.8/Re/sub 0.2/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub y/ had smaller and randomly oriented grains. Measured T/sub c/ values for HgRe1212 and Hg1223 phases were 124 K and 134 K, respectively. Both microstructure and magnetization hysteresis measurements suggest that HgRe1212 is a better candidate for applications.