title: Doping effect of CNT and nano-carbon in magnesium diboride bulk.
abstract: We fabricated carbon nanotube (CNT)- and nano-carbon (NC)-doped MgB2 using an in-situ process in order to improve the critical current density (J(c)) at high magnetic field. We then evaluated the effects of the doped carbon content on phase formation, microstructure, and critical properties. CNT had a diameter and length of 5-10 nm and 0.5-1 microm, respectively, and NC was a sphere with a diameter of 5-30 nm. The bulk MgB(2-x)C(x) samples with x = 0, 0.05, and 0.1 for NC and CNT were fabricated by pressing into pellets and then sintered at 900 degrees C for 30 min. NC was more effective than CNT for carbon doping at the B site in MgB2 and, therefore, the NC-doped MgB2 samples had a lower critical temperature (T(c)) of 35.0-34.7 K than that of the CNT-doped samples (36.4-36.1 K). In addition, the J(c)(B) behavior was improved when NC and CNT were doped due to doping effect. Microstructural observation suggested that the nano-sized and unreacted NC particles and the nanodomain MgB2 acted as effective flux pinning centers for the NC- and CNT-doped MgB2, respectively.
authors.affiliation: School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746, Korea.
authors.forename: Jun Hyung
authors.initials: JH
authors.lastname: Lim
authors.forename: Chang Min
authors.initials: CM
authors.lastname: Lee
authors.forename: Jin Hyun
authors.initials: JH
authors.lastname: Park
authors.forename: Jun Hyuk
authors.initials: JH
authors.lastname: Choi
authors.forename: Jong Hyun
authors.initials: JH
authors.lastname: Shim
authors.forename: Jinho
authors.initials: J
authors.lastname: Joo
authors.forename: Young Hee
authors.initials: YH
authors.lastname: Lee
authors.forename: Won Nam
authors.initials: WN
authors.lastname: Kang
authors.forename: Chan-Joong
authors.initials: CJ
authors.lastname: Kim