Exploring the Superconductors with Scanning Electron Microscopy (SEM)

The characterization of materials supports their development and in particular of superconductors, for their technological applications. Scanning electron microscopy (SEM) is one of these characterization techniques, whose data is used to estimate the properties, determine the shortcomings and hence improve the material. The phenomenon of superconductivity initially develops within the grain and eventually crosses over the grain boundaries, leading to the bulk. Hence SEM can be a useful tool to probe the microstructure of the superconductors and the properties related to it. Along with this the Energydispersive Spectroscopy (EDS) can tell about the chemical composition of compounds. Grain size and its connectivity can be seen through SEM and can be correlated with the corresponding properties. The superconducting materials developed for practical applications are some of the complex materials used today. These materials have large number of potential variables such as their processing conditions, composition, structure etc., whose dependence on the superconducting properties have to be analyzed critically. The characterization techniques are the tools that help to reveal and explore both the macro and microstructure of materials. It is known that the larger grains (reduction in grain boundaries) lead to increased pinning type behavior with enhanced Jc [1]. In contrast Rosko et al. [2] reported that Jc is determined by weak links and grain size has little role on it. Also, Smith et al. [3] interpreted reduction of Jc and activation of weak link type behavior with increasing grain size for YBa2Cu3O7-δ (YBCO) polycrystalline samples in terms of microcracks in large grains. The superconducting parameters are broadly divided into two categories; first, the intrinsic parameters such as penetration depth (┣), which are intrinsic to the material and are not affected by, grain size. On the other hand, values such as shielding/Meissner fraction, the interand intra-grain critical current density and diamagnetic fraction depend upon particle size of bulk superconductors. Thus SEM can be very important to probe and in understanding the superconducting phenomena.