An investigation of the PrBa₂Cu₃O_7−δ system

Abstract

Members of the PrBa₂Cu₃O_7−δ system possessing the orthorhombic structure over a wide range of oxygen stoichiometry (δ=−0.5 to +0.5) have been prepared and characterized. Similar compositions with a tetragonal structure have also been prepared. None of the oxides is superconducting, independent of the structure or stoichiometry. Praseodymium seems to be present to a small extent in the 4+ state in oxygen-excess (negative δ) samples. Orthorhombic PrBa₂Cu₃O_7−δ samples show the presence of twins suggesting that twins arise from orthorhombicity and have no relation to the superconductivity. A neutron diffraction study of a near-stoichiometric sample has shown a disordered orthorhombic structure with 72% occupancy of the 01 (chain) sites and with no interchange between Pr and Ba sites.