TEM and SEM studies on the formation of superconducting phases in the Bi-based system

We present the formation mechanism and structure of the superconducting phases in the Bi–Sr–Ca–Cu–O system by TEM and SEM observations. Oxalate coprecipitation was used as preparation method. The average particle size, distribution and the presence of different phases and shapes of the particles were evaluated. All samples were well crystallized, showing grains in submicronic range. After thermal treatments, the complex samples showed mica-like crystals uniform dispersed and also an orientation tendency. The superlattice was composed of building blocks and successive planes. The TEM observations were in agreement with the diffraction patterns that revealed a mixture of 2212 and 2223 superconducting phases. With the building blocks in the system, it is possible to form many incommensurate phases that destroy the symmetry. Careful control of the preparation conditions is essential to produce a well-ordered commensurate phase, suitable for the precise determination of the complete superstructure by X-ray diffraction.