Structure-property relationships for RBa2Cu3O(x) phases

The relationship between the structure of 1-2-3 compounds of the type RBa2Cu3O(x) and their properties as high-temperature superconductors was investigated using the high-resolution Guinier X-ray powder diffraction technique to determine whether a given compound was tetragonal or orthorhombic; powder neutron diffraction data were used for the refinement of the phases by the Rietveld profile technique. Orthorhombic symmetry was found for the superconducting phases NdBa2Cu3O(6.85), YBa2Cu3O(6.91), and ErBa2Cu3O(6.99). The tetragonal phase of YBa2Cu3O(x) composition and the La(1.5)Ba(1.5)Cu3O7 compound with the tetragonal 1-2-3 structure were found to be not superconducting. The nonsuperconducting tetragonal structures also lacked linear -(Cu-O)- chains, indicating that the linear -(C-O)- chain structure is required for superconductivity.