A new oxycarbonate superconductor (Cu 0.5C 0.5) 2Ba 3Ca 2Cu 3O 11 ( Tc=91 K) prepared at high pressure

Abstract

We prepared a new oxycarbonate superconductor, (Cu 0.5C 0.5) 2Ba 3Ca 2Cu 3O 11 at 1250°C under 5 GPa. This phase is the m=2 and n=3 member of a homologous series, (Cu 0.5C 0.5) m Ba m+1 Ca n-1 Cu n O 2 m+2 n+1 reported previously. Its X-ray pattern could be indexed assuming a tetragonal subcell with a=3.852(1), c=18.61(2) A ̊ . Electron microscopic observations indicated ordering between Cu and C in the (Cu, C) plane, resulting in a superlattice, a s =2 a, b s = b and c s =2 c with respect to the tetragonal subcell. This new member showed a superconducting transition at 91 K.