SEARCH FOR THE ORIGIN OF GIANT T-C SUPPRESSION IN YBA2CU3O7-D DOPED SIMULTANEOUSLY WITH FE AND ZN

In a recent paper [S.B. Ogale et al., Solid State Commun 89 (1994) 1] we reported that the superconducting transition temperature (T-c) is s uppressed drastically in YBa2Cu3O7-d (YBCO) doped simultaneously with Fe and Zn as compared to an equivalent total doping of Zn or Fe, on th e higher side of dopant concentration (approximately 3% or more substi tution at Cu sites). In this paper, we report the results of our studi es on this co-doped system, performed using the techniques of Mossbaue r spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, a nd iodometry, to explore the origin of the reported observation. The T -c suppression appears to be caused by a drop in the concentration of mobile holes in the CuO2 planes as well as to be due to a reduced dime nsionality of the system resulting from the suppression of the order p arameter between the CuO2 planes by the Fe atoms.