Suppression of T-c in the (Y0.9Ca0.1)Ba2Cu4-xFexO8 system

Abstract

In this paper, the effects produced by iron substitutions in the (Y0.9Ca0.1)Ba2Cu4-xFexO8 system on the Superconducting and structural properties are studied. The Rietveld-fit of the crystal structure and Mossbauer spectroscopy results of (Y0.9Ca0.1)Ba2Cu4-xFexO8 samples indicate that the iron atoms occupy the Cu(1) sites of the (Cu-O)(2) double chains in fivefold coordination at low iron concentrations. Besides at high iron concentrations the iron atoms occupy the Cu(I) sites of single Cu-O chains and Cu(2) sites in the CuO2 planes of the (Y0.9Ca0.1)Ba2Cu4O8 phase with structural defects. Simultaneously, as iron concentration increases, a faster decrease of T-c is observed in this material compared with the YBa2Cu3-xFexO7-delta system. According to the charge-transfer model proposed for YBa2Cu4O8 under pressure, the decrease in the Cu(1)-O(4) bond length in parallel to the increase in the Cu(2)-O(4) bond length may affect the charge-transfer mechanism leading to the suppression of T-c.