Synthesis and structure of PrBa₂Cu₂Co₁O_7+y: a new nonsuperconducting orthorhombic 123 system

Abstract

PrBa₂Cu_3-xCo_xO_7+y (0 < x < 1) crystallizes in tetragonal structure for small values of x (0.1 < x < 0.3) and in orthorhombic structure for 0.4 < x < 1, as revealed by X-ray and electron diffraction studies. The end member PrBa₂Cu₂CoO_7.4 shows orthorhombic to tetragonal structural transition with decrease in oxygen content just as YBa₂Cu₃O_7-y(123) and PrBa₂Cu₃O_7-y (Pr123). From the structure and reactivity, the Co ion in PrBa₂Cu₂CoO_7+y is suggested to occupy the Cu(2) (plane Cu) position and the oxygen excess over 7 to occupy the (0, 0, 1/2) position between the CuO₂-CuO₂ (CoO₂) sheets. The structure supports two types of labile oxygen, one associated with the chain Cu(1) and the other in the interlayer associated with the Co ion, as revealed by anaerobic oxidation of ammonia.