Iron doping effect on composition and microstructure of Bi2.05Sr1.9Ca1.05 (Cu1-xFex)(2)O8+delta(0 <= x <= 0.15) superconductors

Samples with Bi2.05Sr1.9Ca1.05(Cu1-xFex)(2)O8+delta (0 less than or equal t o x less than or equal to 0.15) compositions were synthesized by a liquid-m ix process able to give single phase compounds. The superconducting phase w as carefully investigated by SEM and EDX. Substitution of x Fe atoms in the Bi2Sr2CaCu2O8+delta grains corresponds to the removal of 1.7x Cu atoms and to the addition of 0.75x Bi atoms whereas the sum Sr + Ca remains quite co nstant. In a first step, this evolution may be explained by the following b asic model. Fe2O3-->2Fe(cu)(.) + V-cu" + 3 CuO which assumes the creation o f vacancies in the copper sites of the Bi2Sr2CaCu2O8+delta lattice. However , the apparent increase of Bi content suggests the formation of microdomain s of Bi2Sr2CuO6 phase intergrown in the Bi2.05Sr1.9Ca1.05(Cu1-xFex)(2)O8+de lta grains, as inferred from X-ray diffraction and SEM which reveals the co ncomitant (SrCa)(14)Cu24O41 secondary phase. The EDX results are more consi stent with a Bi2Sr2CuO6-Bi2Sr2CaCu2O8+delta intergrowth model in which Fe i s accommodated in the Bi2Sr2CuO6 microdomains than with the model of substi tution in a Bi2Sr2CaCu2O8+delta single phase. (C) 1999 Elsevier Science Lim ited All rights reserved.