Structural phase diagram for superconducting cuprates. Solid state processing for enhanced flux pinning

The phase boundaries in the Y/Ba/Cu/O system for 1-2-3, 2-4-7 and 1-2-4 are determined and each of these defines a possible domain for solid-state heat-treatment to produce flux-pinning precipitates. Thirteen cuprate perovskites are examined and all with Tc > 60 K have a common low pressure boundary which coincides with the boundary between CuO and Cu2O. By phase transformation of La-substituted 1-2-4 over this boundary to La 1-2-3, flux pinning is enhanced 20-fold at 77 K and 50-fold at 85 K relative to unsubstituted 1-2-3. (orig.)