Visualization of the formation of the (Bi,Pb)(2)Sr2Ca2Cu3O10+delta phase

The morphological transformations occurring in the precursor powders during the formation of the (Bi, Pb)(2)Sr2Ca2Cu3O10+delta phase were investigated by scanning electron microscopy performed on the same location on the surface of a pellet, which underwent several heat treatments at 852 degrees C for various times. Following the evolution of a given group of grains we have found that the formation of the (Bi, Pb)(2)Sr2Ca2Cu3O10+delta crystals occurs simultaneously with a gradual decomposition of the intermediate (Bi, Pb)(2)Sr2CaCu2O8+delta phase. This result was confirmed by microprobe analysis as well as x-ray diffraction performed on the same samples. As a main result, we conclude that in the observed powder mixtures, the (Bi, Pb)(2)Sr2Ca2Cu3O10+delta phase does not form from the pre-existing (Bi, Pb)(2)Sr2CaCu2O8+delta crystallites but through a nucleation and growth process. Based on the present observations, a model for the phase formation mechanism of (Bi, Pb)(2)Sr2Ca2Cu3O10+delta is presented.