From SrCuO2 to Sr8Cu8O20−y: Why Are Superconducting Properties of Infinite-Layer Compounds so Poor?

A series of infinite-layer compounds NdxSr1−xCuO2 were synthesized by high-pressure technique under different pressure, temperature, and time conditions. Crystal structure, microstructure, and superconducting properties of the samples obtained were systematically investigated as a function of the synthesis conditions. The stability of the IL phase was studied using annealing procedures in Ar- and O2-flow, as well as under oxygen pressure up to 90 bar followed by thermogravimetric, energy-dispersive X-ray analysis, and X-ray diffraction measurements. On the basis of the results obtained we suggest a decomposition mechanism for the infinite-layer phase, which is responsible for the degradation of Tc, as well as a routine to produce electron-doped infinite-layer compounds with a sharp diamagnetic signal of bulk superconductivity.