Effects of a liquid carbon dopant on the superconducting properties of MgB 2
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Effects of a liquid carbon dopant on the superconducting properties of MgB2 Hyo Jin. Kim1,2 , Bong Kun. Lee1, Chan Joong. Kim2 , Kyu Mann. Lee and Hai Woong. Park1 1
Dept,of Materials Engineering , Korea University of Technology and Education, 1800 Chungjeallo, Byeongcheon-Myeon, Cheonan-City, Chungnam Province, Korea 2 Nuclear Nanomaterials Development Laboratory, Korea Atomic Energy Research Institute, 150 Dukjin-dong, Yuseong-gu, Daejeon 305-353, Korea
ABSTRACT Various types of chemical doping have been reported as very effective methods to improve the superconducting properties of MgB2 superconductor. Specially, carbon doping via liquid type of carbon-containing compounds have been shown better superconducting properties. In this work, the liquid type of glycerin (C3H8O3) was used as a carbon dopant in MgB2 synthesis. The glycerin was mixed with a liquid media at a different ratio and then pretreated with refined boron powder. Then carbon doped MgB2 superconductor was synthesized through subsequent heat treatment of the pretreated boron powder with magnesium powder. Variation of the amount of carbon dopants and viscosity of the liquid media was correlated with critical current densities and other superconducting properties of MgB2 bulk. The effects of liquid carbon dopants on the superconducting properties also compared with those of solid dopants.
INTRODUCTION Since the discovery of Magnesium diboride( MgB2 ) at 39K [1] , the superconductivity of MgB2 bulk superconductor has been researched steadily. In these paper, the superconducting properties of MgB2 superconductor are enhanced by chemical doping. Specially, carbon-based compounds have been proved to be an effective materials for improving superconductivity such as critical current density(Jc) and upper critical field (Hc2) [7] . Glycerin is C3H8O3 and C source. It can be used as milling medium for doping. In this study, the effects of Glycerin as liquid carbon dopants on the superconducting properties of MgB2 bulk was researched.
EXPERIMENT DETAIL In this study, all samples were prepared by an in situ reaction method. The boron powder (95~97%, ~1µm) and various ratios of glycerin(C3H8O3) and alcohol(C2H5O) were attrition milled for 5h at 1000rpm , where glycerin(C3H8O3) was used as the medium. Mg powder and milled B powder were mixed with the nominal atomic ratio of MgB2. And then the mixed powder was pressed into pellets. All samples were sealed in titanium tubes. All MgB2 pellets were sintered at 900oC for 30 min under Ar gas atmosphere in a tube furnace.
MgB2 bulk samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The magnetization was measured at 5 and 20 K using a Magnetic Property Measurement System (MPMS). The magnetic Jc was derived from the width of the magnetization loop using Bean’s model.
DISCUSSION Figure 1. shows magnetic field dependence of critical current density(Jc) for the MgB2 samples at 5 K. The Jc value of glycerin milling MgB2 sample was higher than that of toluen milling
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