Microscopic structural evolution in terms of porosity in high-Tc superconductors

The low critical current densities of high-Tc superconductors materials can be related to the microstructural imperfections such as pores and microcracks, which reduce the effective current carrying cross section. The present work examines the characterisation of the state of microstructure and its evolution during thermal treatment of Bi2Sr2Ca1Cu2O8. The dilatometric analysis was used to study the shrinkage mechanism during sintering. The microstructure of the sintered samples was characterised in terms of pores distribution and apparent density. Open porosity was measured by mercury porosimeter. In order to compare the results, ultrasonic characterisation such as the longitudinal and transverse wave velocities in the ceramic was carried out. From an ultrasonic point of view, these microstructural features act as inhomogeneities and the ultrasonic parameters will depend on the geometrical arrangement of microstructure (pores have an effect both on Young’s modulus and attenuation).