Spatial variations in composition in high-critical-current-density Bi-2223tapes

A detailed compositional analysis of high-critical-current-density (J(c)) ( 55 and 65 kA/cm(2) at 77 K) (Bi,Pb)(2)Sr2Ca2Cu3Oy (Bi-2223) tapes was under taken by energy dispersive spectroscopy in the transmission electron micros cope. Structural features were coupled with characteristic compositions of the Bi-2223 phase. The average of all compositional measurements of the Bi- 2223 phase was determined to be Bi1.88Pb0.23Sr1.96Ca1.95Cu2.98Oy. However, spatial variations in the Bi-2223 composition and differing phase equilibri a were found throughout the filament structure. In particular, a considerab le range of Bi-2223 compositions can be found within a single tape, and the lead content of the Bi-2223 phase is significantly depressed in the vicini ty of lead-rich phases. The depletion of lead in the Bi-2223 phase around t he 3221 phases may be a current-limiting microstructure in these tapes.