Fe-57, Sn-119 and Eu-151 Mossbauer studies of (Tl,Pb)(Ba0.2Sr0.8)(2)Ca2Cu3O gamma superconductors

The introduction of the Mossbauer nuclei Fe-57, Sn-119 and Eu-151 into T1-b ased 12(n - l)n superconductors was investigated. The doped T1-based superc onductors were characterized with respect to critical temperatures, critica l currents, microstructure and composition of the superconducting and secon dary phases. The samples were then analyzed by Mossbauer spectroscopy. Ener gy dispersive X-ray (EDX) analysis showed that both Fe-57 and Eu-151 were i ncorporated in the superconducting crystallites. Sn was found in secondary phases. Incorporation of Eu into the superconducting phase favored the form ation of the T1-1212 phase. The isomer shift and the electric field gradien t derived from the Eu-151 spectra were consistent with Eu3+ at the Ca site. The Fe-57 Mossbauer spectra refer to two different micro-environments for the Fe3+ They were assigned to Fe3+ substituting Cu between the two Ca laye rs and between the Ca and Ba-Sr-O layers. (C) 1999 Published by Elsevier Sc ience B.V. All rights reserved.