⁵⁷Fe and⁵⁷Co Mössbauer study of suppression of superconductivity in PrBa₂Cu₃O_7−d

Abstract

⁵⁷Fe and⁵⁷Co Mössbauer spectroscopy and X-ray diffractometry were used to study⁵⁷Fe- and⁵⁷Co-substituted PrBa₂Cu₃O_7−d samples. Our most striking result is that the isomer shifts belonging to both Co and Fe at four- and five-coordinated Cu(1) sites in the PrBa₂Cu₃O_7−d cuprate are significantly higher than those observed for the superconducting 1-2-3 compounds. This result is considered as being a consequence of suppression of superconductivity because the extra electrons from Pr fill in the holes in Cu-O planes due to the valence state of Pr higher than 3+ and due to hybridization of Pr-Cu-O orbitals, via the charge transfer mechanism between the Cu(2)-O planes and Cu(1)-O chains. Our results give evidence of the existence of the charge transfer mechanism between the planes and the chains, and of its important role in controlling the superconductivity with a charge reservoir behavior of the Cu(1)-O chains.