In-situ and ex-situ PIT fabrication of FeSe superconducting tapes

Abstract

FeSe Superconducting tapes were fabricated with powder in tube (PIT) process. Both in-situ and ex-situ PIT processes were performed with Se and sintered Fe–Se powders as precursor powders, respectively. The influences of different fabrication techniques on the phase evolution mechanism, morphology and superconducting properties of these tapes were systematically investigated. It was noticed that during the in-situ PIT process, large content of tetragonal β-FeSe phase could be formed under low temperature. However, the obtained β-FeSe phase was not stable with increasing temperature and decomposed into δ-FeSe and Fe. Although with increasing temperatures, β-FeSe phase content increased again, the final β-FeSe phase content could not reach 100%, with relatively large content of δ-FeSe particles distributed uniformly in β-FeSe matrix. On the other hand, during the ex-situ PIT process, higher temperature was necessary for the formation of higher ratio of β-FeSe phase from δ-FeSe phase. With the increasing temperature, β-FeSe phase content increased monotonously, and the β-FeSe content of nearly 100% was obtained under the sintering temperature of 1000 °C. Due to the different Fe/Se ratio in the obtained β-FeSe phase, a superconducting transition at 8.3 K was obtained on the ex-situ FeSe tape. Further optimization of this PIT process for larger superconducting phase content is on the way.