Formation of the High-T_c Phase in Rapidly Quenched Bi-Pb-Sr-Ca-Cu-O Ceramics

Abstract

Amorphous ceramics with the composition of Bi2Pb0.4Sr2Ca2Cu3O y were prepared by rapid quenching. The change in crystalline structure during annealing and the effect of the “seeding” with the high-T c phase were investigated. The volume fraction of the high-T c phase increases with annealing time; however, the low-T c phase reaches a maximum value of 38% for 1 h annealing and decreases on prolonged annealing. The formation rate of the high-T c phase changes when the volume of the high-T c phase reaches about 30%. TEM observation shows that the high-T c phase is often located between the low-T c phase and the nonsuperconducting phase. The addition of the seed crystals with the high-T c phase is effective in forming the high-T c phase in shorter annealing times, but a smaller volume fraction of the high-T c phase was obtained after annealing for 50 h.

Bi-2223 grain growth in Ag/Ni composite-sheathed tapes sintered at different oxygen partial pressures

“…The Avrami equation was used to analyze the growth kinetics of Bi‐2223 grains sintered at different atmospheres . This equation has been found to be well suited to describe the growth kinetics of Bi‐2223 phase , which is expressed as follows: where V is the volume fraction of Bi‐2223 phase after sintering, t is the sintering time, n is the reaction order dependent on the nature and the characteristics of the Bi‐2223 phase transformation, and k is the rate constant that obeys the Arrhenius equation. According to Rao and Rao , in the case of diffusion‐controlled transformation, the exponent n can take values of: (i) n = 2.5 – initial growth of particles nucleated at constant rate; (ii) n = 1.5 – initial growth of particles nucleated at the start of the transformation; (iii) n = 1 – growth of isolated plates or needles of finite size; (iv) n = 0.5 – thickening of plates after their edges have impinged.…”

“…The Avrami equation was used to analyze the growth kinetics of Bi-2223 grains sintered at different P O 2 atmospheres [19]. This equation has been found to be well suited to describe the growth kinetics of Bi-2223 phase [18,[20][21][22][23][24][25], which is expressed as follows:…”

Effect of precursor phase assemblage on densification and critical current density of (Bi,Pb)-2223 superconductor

“…Since the fractions of 2212 and Ca 2 PbO 4 in the precursors P1 and P2 are higher (Table 1), the amount of liquid phase in the initial stages of the reaction will be larger. This makes the reaction faster and leads to the formation of very large single crystal-like 2223 platelets oriented in random directions leaving large voids [18,20] between them (Fig. 6).…”

A new model for the formation of high-T c phase in superconductive (Bi, Pb)2Sr2Ca2Cu3O x glass-ceramics

“…The difficulty in preparing the high-T~ phase revealed that an understanding of the formation of high-T~ phase is prerequisite for the fabrication of superconductors containing pure high-To phase with high quality. The formation mechanism of the high-To phase was extensively discussed by many authors [6][7][8][9][10][11]. Even 0957 4522 ~; 1996 Chapman & Hall though different approaches were made so far, many points concerning the formation mechanism of the high-To phase are still obscure.…”