High Critical Temperature Superconducting Oxides of the YBCO System

Most materials used in superconductivity studies belong to the family of copper oxides \( \text {RBa}_2\text {Cu}_3\text {O}_{7-\delta } \) where R is a rare earth element. The majority of these compounds are perovskite-type ABO \(_3\) oxygen-deficient superconductors with high critical temperatures. They possess a layered structure along the c-axis, composed of \( \text {CuO}_2 \) planes determining the superconducting character of these materials and \( \text {Cu-O} \) chains acting as charge reservoirs for the \( \text {CuO}_2 \) planes. The oxygenation state of the \( \text {Cu-O} \) chains determines the structure of these compounds as well as their anisotropy in the (a,b) plane.