Superconductivity in the A-Cu-O System (A: alkaline-earth)

Abstract

Cupric oxide superconductors are made of 2D CuO₂ sheets and 2D counter sheets stacked alternatively along a crystallographic axis. These sheets match their 2D lattices through intersheet metal-oxygen bonding. Because the Cu-O and counter cation-O bonds should have different compressibilities and different thermal expansion coefficients, it is quite reasonable to assume that preparation in various pressure-temperature regions give us new materials having new structures and/or new compositions.
We found previously that the so-called infinite layer structure could be stabilized at high pressure (6GPa) for a much wider alkaline earth composition range including SrCuO₂ than at ambient pressure. Fortunately we recently found a superconductor with Tc-110 K having an alkaline earth deficient composition (Sr, Ca)_1-xCuO₂ (x-0.1).