Superconductivity at 110 K in the infinite-layer compound (Sr 1-xCax)1-yCuO2

Abstract

THE 'infinite-layer' parent structure1 of the copper oxide superconductors (Fig. 1) is the simplest structure containing the CuO 2 sheets that are apparently essential to high-transition-temperature (high-Tc superconductivity. At ambient pressure only Ca 1-x SrxCuO2 with x≈O.l can be stabilized in this structure1,2but at high pressures and temperatures compounds ranging from Ba1/3Sr2/3CuO 2 to Ca2/3Sr1/3CuO 2 through SrCuO2 can be synthesized3. We have previously reported superconductivity with Tc = 40-100 K in the Ba-Sr-Cu-O system4,5 but have not until now been able to isolate a superconducting phase. Here we report the isolation of an alkaline-earth- deficient infinite-layer phase, (Ca1-xSrx) 1-yCuO2 (y~O.l), with Tc up to 110 K. In contrast to Sr1-xRxCuO2 (with R a rare-earth element and Tc≤43 K), which from the composition dependence of the lattice constants is thought to be an n-type superconductor6,7 our data suggest that the present superconductor is of p-type, with the carriers arising from calcium and strontium vacancies. High-resolution electron micrographs reveal defect layers, which we suggest are where the calcium and strontium vacancies are concentrated. © 1992 Nature Publishing Group.