Relationships of structure to properties of various type RBa2Cu3Ox compounds

Verification of the structure of certain RBa2Cu3Ox type compounds is carried out using the neutron diffraction analysis of a powder at 298 K. The superconducting NdBa2Cu3O6.85, YBa2Cu3O6.91 and ErBa2Cu3O6.99 phases are shown to have the rhombic symmetry. In some rare-earth elements Cu-O short distance (∼ 0.185 nm) decreases with the growth of the rare-earth metal cation size, but the average Cu-O distance in extended chains remains practically constant. Verification of the structure of the YBa2Cu3O7-x phase has shown that transition to tetragonal modification of the YBa2Cu3O6 composition occurs without structure destruction. The latter phase possesses semiconducting properties and it is not a superconductor. On the basis is supposed that superconductivity in perovskites deficient by oxygen is caused by the presence of (-Cu-O-)n-chains. 5 refs.; 1 fig.; 4 tabs