The structural and superconducting properties of orthorhombic and tetragonal $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ have been determined for a wide range of stoichiometries ($0.3<x<\mathrm{}0.7\mathrm{}$). In the orthorhombic phase, $T_c$ decreases smoothly as $x$ increases and reaches zero at the orthorhombic-to-tetragonal transition. Tetragonal $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ is not superconducting at any stoichiometry. This systematic depression of $T_c$ is correlated with the decrease in the oxygen content which alters the electronic structure of the Cu-O networks.

• Received 9 July 1987

DOI:https://doi.org/10.1103/PhysRevB.36.5731