NEUTRON-DIFFRACTION STUDY OF PR VALENCE AND OXYGEN ORDERING IN THE Y1-XPRXBA2CU3O7-DELTA SYSTEM

The crystallographic changes that occur with increasing Pr concentration in the Y-xPrxBa2Cu3O7-δ system have been studied by neutron diffraction. As x is increased from 0 to 1, the orthorhombic a, b and c lattice parameters expand monotonically, while the orthorhombic distortion, espressed as b a, decreases, reflecting increased occupation of O(5) sites at the expense of O(4) chain site occupancy. The separation of the CuO2 planes in PrBa2Cu3O7-δ indicates that the Pr ions have an intermediate valence of ∼3.3 in this compound. Evidence is presented for increased interaction between the Pr ions and oxygen ions in adjacent CuO2 planes. © 1990.