The synthesis of (Bi,Pb)2Sr2Ca2Cu3Ox(2223) by the diffusion-couple technique

The formation of (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x (2223) by various reaction paths was studied by diffusion experiments on selected composition couples in the Bi(Pb)-Sr-Ca-Cu-O system at 810-850 degrees C and analysed by electron microscopy and EDX. An important grain growth of 2223 at the interface between solid pellets was observed in the following diffusion-couple configurations: (i) (Ca 0.5 Sr 0.5 )CuO 2 +(Bi,Pb) 2 CuO 4 at 845 degrees C and (ii) (Ca 0.85 Sr 0.15 )CuO 2 ("n= infinity " phase)+Pb-doped 2212 at 835-852 degrees C. The presence of a liquid phase is noted in both cases. 2223 crystals up to 100 mu m long growing perpendicular to the diffusion front were obtained in 4 d for both composition assemblages. The critical temperature of the diffusion zone product was 108 K. In case (ii), it is shown that the (Ca 0.85 Sr 0.15 )CuO 2 phase is unstable with respect to (Ca,Sr) 2 CuO 3 and CuO in the temperature range 827-852 degrees C.