Formation pathways in the synthesis and properties of (Ti0.5Pb0.5)(Sr0.9Ba0.1)(2)Ca2Cu3Oz and (Ti0.5Pb0.5)(Sr0.8Ba0.2)(2)Ca2Cu3Oz-1223 superconductors

Abstract

International audienceThe formation pathway of ( Tl0.5Pb0.5)( Sr0.9Ba0.1)(2)Ca2Cu3Oz and (Tl0.5Pb0.5)(Sr0.8Ba0.2)(2)Ca2Cu3Oz was studied by neutron and x- ray diffraction. The following reaction pathway was proposed: thallium oxide and lead oxide react with Sr- rich ( Sr(1-x)Cax) CuO2 and Ca-rich ( CaxSr1-x)O to form Sr4Tl2O7 and ( Cax Sr1-x) PbO3, respectively. The thallate and the plumbate compounds then form the ( Tl0.5Pb0.5)-1212 phase starting at a temperature of 600 degrees C. Finally, between 850 and 900 degrees C, the 1223 phase is formed from (Tl0.5Pb0.5)-1212, ( CaxSr1-x)(2)CuO3 and CuO. Parallel experiments to fabricate the ( Tl, Pb)- 1223 superconductor resulted in specimens with critical temperatures of 117.5 K and 116 K, respectively, and transition widths of 2 K. Differences between the pathways for the formation of Pb- doped, Sr- rich and Pb- free, Ba- rich Tl- 1223 superconductors are discussed