FE-57 AND CO-57 MOSSBAUER STUDY OF SUPPRESSION OF SUPERCONDUCTIVITY IN PRBA2CU3O7-D

Fe-57 and Co-57 Mossbauer spectroscopy and X-ray diffractometry were u sed to study Fe-57- and Co-57-substituted PrBa2Cu3O7-d samples. Our mo st striking result is that the isomer shifts belonging to both Co and Fe at four- and five-coordinated Cu(1) sites in the PrBa2Cu3O7-d cupra te are significantly higher than those observed for the superconductin g 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 mechanis m between the planes and the chains, and of its important role in cont rolling the superconductivity with a charge reservoir behavior of the Cu(1)-O chains.