We investigated the effects of adding indium, lead or tin to SmFeAsO1-xFx. It is found that these metal additions to polycrystalline SmFeAsO1-xFx remove an amorphous FeAs phase, which is formed between superconducting grains, and induces clustering of the superconducting grains. Interestingly, addition of each metal showed different effects on the superconductivity. Indium addition increases the magnetic critical current density. Lead addition effectively introduces a large amount of fluorine to SmFeAsO1-xFx. Tin addition enhances coupling between the superconducting grains.
High-temperature superconducting (HTS) power devices such as power cables, transformers, current limiters, and superconducting magnetic energy storage (SMES) are approaching the stage where they can be adopted for practical use. A cooling system requires cooling capacity of 2 to 10 kW at 65 K and high COP, and is also required to be maintenance-free and compact. However there are no adequate cooling systems among commercial systems. Therefore, we are developing a turbo-Brayton cycle refrigerator using neon gas as the working fluid with cooling capacity of 2 kW at 65 K. Details of the turbo-Brayton cycle refrigerator are described in this paper.