Formation mechanism of the Pb free Bi2Sr2Ca2Cu3O10 phase

The reaction leading to the formation of the Pb free Bi2Sr2Ca2Cu3O10+δ phase from calcined precursor powders has been studied by means of scanning electron microscopy, x-ray diffraction and differential thermal analysis. The observation of the transformations occurring at a fixed location on the surface of a pellet has shown that the formation of the Bi2Sr2Ca2Cu3O10+δ phase crystallites occurs simultaneously with a gradual decomposition of the Bi2Sr2CaCu2O8+δ platelets initially present in the mixture. The present investigations are discussed in relation with the formation of the Pb substituted (Bi, Pb)2Sr2Ca2Cu3O10+δ phase. It is shown that there is a close relationship between the formation mechanisms of the Pb free and the Pb substituted phases, which both can be described as a nucleation and growth process. (author)