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Comparison of in-situ $MgB_2$ Superconducting Properties Under Different Annealing Environment
정국채,장세훈,김정호,Chung, K.C.,Sinha, B. B.,Chang, S.H.,Kim, J.H.,Dou, S. X. The Korean Superconductivity Society 2012 Progress in superconductivity Vol.14 No.2
Effect of mixed gas and additional Mg powder in an annealing process of the $MgB_2$ is investigated. Four different type of samples were prepared, each in different annealing environment of Ar, $Ar+4%H_2$, Ar with Mg powder and $Ar+4%H_2$ with Mg powder. Different annealing environment did not affect the electron-phonon interaction which is reflected from the same superconducting transition of 36.6 K for all samples. The reducing effect of hydrogen is clearly depicted from the presence of excess Mg in sample synthesized in $Ar+4%H_2$ gas implying the reduced rate of reaction between Mg and B. This has manifested itself in terms of slightly increased high-field critical current density of the sample. In contrast, the sample synthesized in $Ar+4%H_2$ with Mg powder, has shown overall enhancement in the superconducting properties as presented by higher diamagnetic saturation and critical current density.
Improved critical current density in MgB₂ by graphene nano-platelets
B.B.Sinha,정국채,장세훈,김정호,S.X.Dou 한국초전도학회 2012 Progress in superconductivity Vol.14 No.1
The effect of graphene inclusion in the ex-situ MgB2 was analyzed with the help of resistivity behavior and critical current density studies. Amount of graphene was systematically varied from 0% for pristine sample to 3% by the weight of MgB2. Graphene that is considered as a good source of carbon was found to be intact without any significant carbon doping in MgB2structure as reveled by XRD measurements. There was no signature of graphene inclusion as far as the superconducting transition is concerned which remained same at 39 K for all the samples. The transition width being sensitive to defect doping remained more or less about 2 K for all the samples showing no variation due to doping. Although there was no change in the superconducting transition or transition width, the graphene doped sample showed noticeable decrease in the overall resistivity behavior with respect to decrease in temperature. The graphene inclusion acted as effective pinning centers which have enhanced the upper critical field of these samples.
Fabrication of Magnesium Diboride Thin Films by Aerosol Deposition
B.B.Sinha,정국채,장세훈,한병동,박동수,X. L. Wang,S. X. Dou 한국초전도학회 2011 Progress in superconductivity Vol.13 No.2
Superconducting MgB2 thin films were fabricated by using a novel aerosol deposition technique wherein the pre-reacted powder is directly transformed into respective thin film. The formed thin films were characterized by X-ray diffraction technique and FE-SEM to understand its structure and morphology and the superconducting behavior has been characterized with the four probe resistivity measurement. The as-deposited thin films were formed into the frustrated amorphous structure,which were relaxed on the further heat treatment at 900 °C for 3 hrs. The relaxed amorphous MgB2 thin films showed a comparatively high superconducting onset at about 38 K.
Collective effect of hydrogen in argon and Mg as ambiance for the heat treatment on MgB<sub>2</sub>
Sinha, B.B.,Jang, S.H.,Chung, K.C. The Korea Institute of Applied Superconductivity a 2014 한국초전도저온공학회논문지 Vol.16 No.2
Magnesium diboride superconductor is still of considerable interest because of its appealing characteristics towards application mainly at around 20 K. Unlike Nb-based superconductors, $MgB_2$ can be operated by cryogen-free cooler which provides a cost effective alternative at low field of around 2-5 T. To explore this operating field region considerable efforts are necessary to marginally improve the superconducting properties of $MgB_2$. Under this situation, even the heat treatment environment during the synthesis is considered as an important factor. The addition of $H_2$ gas in small amount with Ar as a mixed gas during annealing has an adverse effect on the superconducting properties of $MgB_2$. It is although interesting to find that the presence of Mg vapor along with hydrogen during heat treatment results in the appreciable improvement in the flux pinning and the overall response of the critical current density for the ex-situ $MgB_2$ samples.