Processing of Superconducting and Thermoelectric Bulk Materials Via Laser Technologies

Abstract

As it is well-known bulk high temperature superconductors are used in technological high power applications, as for instance, superconducting fault current limiters or current leads. Due to their intrinsic granularity and anisotropy issues, the superconducting properties of these materials are strongly determined by current percolation problems. This depends on several factors as the characteristics and properties of individual grains and the quality of the grain boundaries. Thermoelectric (TE) harvesting of wasted heat should play an important role in a sustainable future, due to its simplicity, scalability, and self-sustainability in all kind of applications: remote/attended or mobile/static ones. The development of oxide-based TE materials is important when considering that they are cheaper, and possess lower toxicity than the traditional ones. Moreover, oxides can be used at high temperatures without protecting atmospheres, opening new opportunities for energy recovering TE devices. On the other hand, it is desirable to tune up their TE performances before integration in practical applications. In consequence, in order to obtain bulk materials for the technological applications, it is necessary to develop fabrication techniques controlling the microstructure and shape materials. Recently, in order to fabricate the bulk high temperature superconductors and thermoelectrics with high physical properties, the laser technologies have been widely used. In these techniques, the anisotropy arising from the solidification process permits to aligning the grains within the textured bulk material. For this purpose, superconducting Bi2Sr2-xNaxCaCu2Ox and thermoelectric Bi2Sr2-xNaxCo2Ox samples were prepared and textured using the laser floating zone (LFZ) technique. Microstructural analysis of as-grown samples showed well oriented grains and a relatively high amount of secondary phases due to their incongruent melting. Annealing procedure has drastically decreased the number and amount of secondary phases. Moreover, Na-doping has further decreased the secondary phase content and improved grain alignment.