The high temperature superconducting Hg-Ba-Ca-Cu-O (HBCCO) compound system reported by Schilling et al. has been reproduced with an onset transition-temperature (Tc0) up to ≁140 K and a main transition at ≁135 K, after proper heat-treatment. We found a positive pressure-effect on Tc with a rate of 0.17 to 0.18 K/kbar and an irreversibility line at temperatures higher than that in the double Bi and Tl layered high temperature superconductors (HTS's). The observation suggests that the compounds synthesized by us are underdoped and further Tc enhancement (although not drastic) is possible by proper doping, and the HBCCO system appears to be a better candidate than the double Bi and Tl layered HTS's for applications based on the higher irreversibility line.
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