Abstract
A cupric oxide carbonate superconductor with a Tc of 92K has been synthesized under high pressure of 6GPa. A single phase sample with a large Meissner volume fraction of 20% is obtained when a mixture with a nominal composition (Ca0.3Sr0.7)3Cu2 C0.75 Oy encapsulated with an oxidizer of KClO4 is treated at 1473K and 6GPa for 30 minutes. The phase crystallizes basically in tetragonal structure with α=3.851Å and c=10.941Å, while an orthorhombic supercell of α×4α×2c forms, most probably as a result of ordering of carbon vacancies along the b-axis. An irreversibility line was measured under magnetic fields up to 5T.
