title: Influence of nanocrystalline boron precursor powder on superconductivity in MgB2 bulk.
abstract: In this report, high-purity nanocrystalline boron powders processed by ball-milling were used as the precursor powders to fabricate MgB2 superconductor. The transport properties and the critical current density in the samples made from ball-milled boron powders and as-supplied boron powders were investigated. It was found that the ball-milled boron powders led to a significant enhancement of the critical current density in MgB2 sintered at 650 degrees C. The reason can be attributed to the small MgB2 grain size caused by the ball-milled boron precursor powders. The resistivity of the samples made from the ball-milled boron powder was lower than that of the sample from as-supplied boron powder. As the sintering temperature increased, both resistivity and upper critical field decreased in the samples using the ball-milled boron powders as a precursor. Poor connectivity and large strain are responsible for the high resistivity.
authors.affiliation: Institute for Superconducting and Electronic Materials, University of Wollongong, Northfields Ave., Wollongong, NSW 2522, Australia.
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhang
authors.forename: Cheng
authors.initials: C
authors.lastname: Lu
authors.forename: Sihai
authors.initials: S
authors.lastname: Zhou
authors.forename: Jinho
authors.initials: J
authors.lastname: Joo