High-Tc superconductivity in regions of possible compound formation: Y2−xBaxCuO4−x/2+δ and Y2−xBa1+xCu2O6−x/2+δ

Abstract

High-$T_c$ superconductivity is investigated in the Y-Ba-Cu-O system. Regions of possible compound formation are ${\mathrm{Y}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Ba}}_{\mathrm{x}}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{x}/2+\mathrm{\delta }}$ and ${\mathrm{Y}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Ba}}_{1+\mathrm{x}}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_{6\mathrm{-}\mathrm{x}/2+\mathrm{\delta }}$. $T_c$ values >90 K are found for the former with x=0.8 (the Chu material) and for the latter with x=0.2 and may imply a common superconductivity phase in both samples. Critical fields determined by resistance and low-field $d_c$ susceptibility measurements are reported.