Superconductivity up to 100 K in lead cuprates: A new superconductor Pb 0.5Sr 2.5Y 0.5Ca 0.5Cu 2O 7−δ

Abstract

A new superconductor Pb 0.5Sr 2.5Y 0.5Ca 0.5Cu 2O 7−δ has been isolated whose superconducting properties depend upon the thermal treatments, i.e. are closely related to the oxygen stoichiometry. This material exhibits a T on c=100 K whereas the T off c ( R=0) ranges from 45 K to 53 K. The magnetic measurements using a SQUID magnetometer show superconducting volume fractions ranging from 14% to 72%. Anomalies appear in the magnetization curves at low field for some samples. This effect and the broad transition are interpreted in terms of an inhomogeneous distribution of oxygen in the matrix. The structure of this tetragonal phase ( a=3.81 Å, c=11.908 Å) belongs to the “1212” type observed for thallium cuprates, i.e. consists of an intergrowth of double rock salt-type layers involving lead and strontium and of double copper pyramidal layers interleaved with yttrium and calcium. This oxide differs also from the classical intergrowth structures by the existence of numerous oxygen vacancies in the rock salt type layers (δ≅0.7−0.5); moreoer satellites are observed on E.D. diffraction patterns. These two effects are explained by the presence of the 6s 2 lone pair of Pb(II).