Pingyuan Li

Phase formation and superconducting properties of mechanically alloyed Nb3(Al1−x Ge x ) system

Mechanically alloyed Nb3(Al1−x Ge x ) compounds with nominal composition x = 0%, 10%, 15%, 20%, 25% and 30% were synthesized using high-energy ball milling. The effects of Ge content and sintering temperature on the formation of the Nb3Al superconducting phase at a relatively low temperature without the extremely high-temperature rapid heating, quenching and transformation process were studied. The results revealed that Ge doping in Nb3Al improved the formation of the A15 phase at low temperatures, enhanced the superconducting transition temperature (T c), and refined the grain structure, thus improving the overall superconducting properties. The pinning behavior was also studied for the optimized sample.

Preparation of Nb3Al by high-energy ball milling and superconductivity

The A15 phase superconductor Nb3Al has been considered as an alternative to Nb3Sn for high field and large scale applications. However, to prepare a stoichiometric Nb3Al with fine grain structures is very difficult. High-energy ball milling is a solid state powder processing technique and is a very useful for preparing Nb-Al alloys (Nb3Al). The effects of ball milling time and annealing temperature on the formation of Nb3Al superconducting phase have been studied. Pure Nb and Al powders with stoichiometric ratio of Nb3Al were mixed and milled, and the charging and milling were performed in an inert atmosphere. Phase formation and structural evolution during high-energy ball milling have been examined by X-ray diffraction. Al disappeared and Nb peaks broadened after about one hour of milling. With increasing milling time, the peaks of Nb became considerably broader and intensities decreased, the Nb-Al solid solution phase was extensive when milled about 3 hours. In order to obtain Nb3Al superconducting phase, a subsequent anneal was required. We have annealed the as-milled powders at 800-900°C for different times to prepared Nb3Al superconducting alloy. The results indicated that Nb3Al with small amount of impurity phase can be obtained on annealing the Nb-Al solid solution phase and the superconducting transition temperature was about 15K, but it is difficult to obtain a homogeneous Nb3Al phase by annealing the amorphous powder.