STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF OXYGEN-DEFICIENT NDBA2CU3O7-DELTA

Neutron diffraction was used to determine the structural properties of oxygen deficient NdBa2Cu3O7- for 0.09<<0.74. It was found that superconductivity disappears at the orthorhombic-to-tetragonal phase transition which occurs at OT=0.45. Structural parameters vary smoothly with but exhibit a change in slope at the orthorhombic-to-tetragonal transition. The structural properties exhibit the same features found in YBa2Cu3O7- where OT=0.65. It is shown that the repulsion energy of oxygen atoms in the O(1) and O(5) sites in NdBa2Cu3O7- is smaller than in YBa2Cu3O7-. This lower repulsion energy stabilizes the orthorhombic phase at lower values of. It is argued that the disappearance of superconductivity at the orthorhombic-to-tetragonal transition is an inherent property of the RBa2Cu3O7- (R denotes rare earth) system. © 1990 The American Physical Society.