FeSe superconducting bulks were prepared with high energy ball milling (HEBM) aided sintering process, within which process, tetragonal β-FeSe superconducting phase could be formed directly with one step sintering process, and the formation of hexagonal δ-FeSe non-superconducting phase was effectively avoided. The influences of HEBM time on the sintering process of FeSe bulks were systematically investigated. With different HEBM time, the phase composition and morphology of precursor powders changed correspondingly, which thus influenced the final phase composition and superconducting properties of FeSe superconducting bulks. Due to the formation of FeSe bulks with larger tetragonal phase content and higher superconducting transition temperature, HEBM time of 6.0 h was recognized as the optimal parameter. Shorter HEBM time could lead to the insufficient decrease of particle size and low density. While longer HEBM time caused the formation of amorphous hexagonal δ-FeSe, which crystallized during sintering process. Thus no more tetragonal FeSe could be obtained. The FeSe superconducting bulk with the critical temperature Tc(onset) of 8.0 K was obtained with the HEBM time of 6 h, and sintering temperature of 700 oC for 12 h.

The effects of BaF2 on thermal behavior and microstructure of melt-processed YBCO superconductors have been investigated. The differential thermal analysis (DTA) results indicated that the peritectic decomposition temperature of YBCO precursor powder was lowered when BaF2 was added (from 1020 to 976). The peritectic decomposition temperature was lowest at the content of 5 wt.% BaF2, and the variation of melting temperature was not significant above 5 wt.% BaF2. The microstructures of the doped samples have been observed by scanning electron microscopy (SEM). The results showed that the of BaF2 microstructure .