Effect of Fe substitution in the structure and superconducting properties of the (Y0.8Pr0.2)Ba2Cu4−xFexO8 system

Abstract The effects of iron substitutions on the superconducting and structural properties of (Y 0.8 Pr 0.2 )Ba 2 Cu 4− x Fe x O 8 were studied. As iron concentration increases, the rate at which T c diminishes with x is the same as for the YBa 2 Cu 4− x Fe x O 8 system, but faster than in the YBa 2 Cu 3− x Fe x O 7− δ system. The Mossbauer spectra of the different samples, together with Rietveld refinements of their corresponding X-ray spectra, indicate that the iron atoms occupy preferably the Cu(1) sites of the double (CuO) 2 chains in fivefold coordination; that is, due to their tri-valency, the iron atoms attract extra oxygen atoms, named O(5), that place themselves along the a -axis in between two adjacent planes of the double (CuO) 2 chains. As x is increased, the Cu(1)–O(4) bond length decreases, whereas the Cu(2)–O(4) one increases. Also, a reduction of the occupation factors of the oxygen atoms in the CuO 2 planes is observed. Some of these changes may be due to the presence of O(5) atoms, which in turn affect the charge-transfer mechanism between the (CuO) 2 double chains and the CuO 2 planes where superconductivity takes place, and could be responsible of the rate at which T c decreases.