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Ranot, Mahipal,Jang, S.H.,Oh, Y.S.,Shinde, K.P.,Kang, S.H.,Chung, K.C. The Korea Institute of Applied Superconductivity a 2016 한국초전도저온공학회논문지 Vol.18 No.1
We have investigated the addition effect of NiO magnetic nanoparticles on crystal structure, microstructure as well as superconducting properties of $MgB_2$. NiO-added $MgB_2$ samples were prepared by the solid-state reaction method. The superconducting transition temperature ($T_c$) of 37.91 K was obtained for pure $MgB_2$, and $T_c$ was found to decrease systematically on increasing the addition level of NiO. X-ray diffraction (XRD) analysis revealed that no substitution of Ni for Mg in the lattice of $MgB_2$ was occurred. The microstructural analysis shows that the pure $MgB_2$ sample consists of plate shape $MgB_2$ grains, and the grains get refined to smaller size with the addition of NiO nanoparticles. At 5 K, high values of critical current density ($J_c$) were obtained for small amount NiO-added $MgB_2$ samples as compared to pure sample. The enhancement in $J_c$ could be attributed to the refinement of $MgB_2$ grains which leads to high density of grain boundaries in NiO-added $MgB_2$ samples.
Ranot, Mahipal,Duong, P.V.,Bhardwaj, A.,Kang, W.N. The Korea Institute of Applied Superconductivity a 2015 한국초전도저온공학회논문지 Vol.17 No.2
$MgB_2$ thin films with superior superconducting properties are very promising for superconducting magnets, electronic devices and coated conductor electric power applications. A clear understanding of flux pinning mechanism in $MgB_2$ films could be a big aid in improving the performance of $MgB_2$ by the enhancement of $J_c$. The fabrication advancement and the understanding of flux pinning mechanism of $MgB_2$ thin and thick films fabricated by using hybrid physical-chemical vapor deposition (HPCVD) are reviewed. The distinct kind of $MgB_2$ films, such as single-crystal like $MgB_2$ thin films, $MgB_2$ epitaxial columnar thick films, and a-axis-oriented $MgB_2$ films are included for flux pinning mechanism investigation. Various attempts made by researchers to improve further the flux pinning property and $J_c$ performance by means of doping in $MgB_2$ thin films by using HPCVD are also summarized.
A safe and cost-effective PMMA carbon source for MgB<sub>2</sub>
Ranot, Mahipal,Jang, S.H.,Shinde, K.P.,Sinha, B.B.,Bhardwaj, A.,Oh, Y.S.,Kang, S.H.,Chung, K.C. The Korea Institute of Applied Superconductivity a 2017 한국초전도저온공학회논문지 Vol.19 No.1
Carbon is proven to be very effective in pinning the magnetic vortices and improving the superconducting performance of $MgB_2$ at high fields. In this work, we have used polymethyl methacrylate (PMMA) polymer as a safe and cost effective carbon source. The effects of molecular weight of PMMA on crystal structure, microstructure as well as on superconducting properties of $MgB_2$ were studied. X-ray diffraction analysis revealed that there is a noticeable shift in (100) and (110) Bragg reflections towards higher angles, while no shift was observed in (002) reflections for $MgB_2$ doped with different molecular weights of PMMA. This indicates that carbon could be substituted in the boron honeycomb layers without affecting the interlayer interactions. As compared to undoped $MgB_2$, substantial enhancement in $J_c(H)$ properties was obtained for PMMA-doped $MgB_2$ samples both at 5 K and 20 K. The enhancement could be attributed to the effective carbon substitution for boron and the refinement of crystallite size by PMMA doping.
Ranot, M.,Kang, W.N. Elsevier 2012 CURRENT APPLIED PHYSICS Vol.12 No.2
The MgB<SUB>2</SUB> coated superconducting tapes have been fabricated on textured Cu (0 0 1) and polycrystalline Hastelloy tapes using coated conductor technique, which has been developed for the second generation high temperature superconducting wires. The MgB<SUB>2</SUB>/Cu tapes were fabricated over a wide temperature range of 460-520 <SUP>o</SUP>C by using hybrid physical-chemical vapor deposition (HPCVD) technique. The tapes exhibited the critical temperatures (T<SUB>c</SUB>) ranging between 36 and 38 K with superconducting transition width (ΔT<SUB>c</SUB>) of about 0.3-0.6 K. The highest critical current density (J<SUB>c</SUB>) of 1.34 x 10<SUP>5</SUP> A/cm<SUP>2</SUP> at 5 K under 3 T is obtained for the MgB<SUB>2</SUB>/Cu tape grown at 460 <SUP>o</SUP>C. To further improve the flux pinning property of MgB<SUB>2</SUB> tapes, SiC is coated as an impurity layer on the Cu tape. In contrast to pure MgB<SUB>2</SUB>/Cu tapes, the MgB<SUB>2</SUB> on SiC-coated Cu tapes exhibited opposite trend in the dependence of J<SUB>c</SUB> with growth temperature. The improved flux pinning by the additional defects created by SiC-impurity layer along with the MgB<SUB>2</SUB> grain boundaries lead to strong improvement in J<SUB>c</SUB> for the MgB<SUB>2</SUB>/SiC/Cu tapes. The MgB<SUB>2</SUB>/Hastelloy superconducting tapes fabricated at a temperature of 520 <SUP>o</SUP>C showed the critical temperatures ranging between 38.5 and 39.6 K. We obtained much higher J<SUB>c</SUB> values over the wide field range for MgB<SUB>2</SUB>/Hastelloy tapes than the previously reported data on other metallic substrates, such as Cu, SS, and Nb. The J<SUB>c</SUB> values of J<SUB>c</SUB>(20 K, 0 T) ∼5.8 x 10<SUP>6</SUP> A/cm<SUP>2</SUP> and J<SUB>c</SUB>(20 K, 1.5 T) ∼2.4 x 10<SUP>5</SUP> A/cm<SUP>2</SUP> is obtained for the 2-μm-thick MgB<SUB>2</SUB>/Hastelloy tape. This paper will review the merits of coated conductor approach along with the HPCVD technique to fabricate MgB<SUB>2</SUB> conductors with high T<SUB>c</SUB> and J<SUB>c</SUB> values which are useful for large scale applications.
Ranot, M.,Seong, W.K.,Jung, S.G.,Lee, N.H.,Kang, W.N.,Joo, J.H.,Zhao, Y.,Dou, S.X. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15
We report on Ag and Cu doping in MgB<SUB>2</SUB> thick films using amorphous Ag- and Cu-impurity layers with various thicknesses, 4, 8, 16, and 32nm. Firstly, Ag- and Cu-impurity layers were deposited on Al<SUB>2</SUB>O<SUB>3</SUB>(0001) substrates at room temperature by using pulsed laser deposition system. Subsequently MgB<SUB>2</SUB> films were grown on the top of Ag or Cu/Al<SUB>2</SUB>O<SUB>3</SUB> substrates at 560 and 600<SUP>o</SUP>C by using hybrid physical-chemical vapor deposition. The effect of Ag and Cu doping as well as growth temperature on the microstructure and critical current density (J<SUB>c</SUB>) of MgB<SUB>2</SUB> films were investigated. It was found that both of Ag/Cu doping and low growth temperature can significantly enhance J<SUB>c</SUB> without suppression of T<SUB>c</SUB>. The increase in J<SUB>c</SUB> results from improved grain connectivity and strong flux pinning by high density of grain boundaries and other types of defects introduced by Ag- or Cu-impurity layers.
Ranot, M.,Cho, K.,Seong, W.K.,Oh, S.,Chung, K.C.,Kang, W.N. North-Holland 2011 Physica. C, Superconductivity Vol.471 No.19
We have investigated the influence of B<SUB>2</SUB>H<SUB>6</SUB> gas mixture flow rate and deposition time on superconducting properties of MgB<SUB>2</SUB> tapes. The MgB<SUB>2</SUB> tapes are fabricated by growing the MgB<SUB>2</SUB> films on Hastelloy tapes at a temperature of 520<SUP>o</SUP>C by using hybrid physical-chemical vapor deposition (HPCVD) technique. The MgB<SUB>2</SUB> tapes exhibit transition temperature (T<SUB>c</SUB>) of around 39K and is found to be unaffected by the gas flow rate but shows a slight dependence on the deposition time. X-ray diffraction analysis revealed that the MgB<SUB>2</SUB> tapes are polycrystalline in nature. MgB<SUB>2</SUB> grains of various orientations are observed in the microstructures of the tapes taken by scanning electron microscopy. We obtained much higher J<SUB>c</SUB> values over the wide field range for MgB<SUB>2</SUB> tapes grown on Hastelloy than the previously reported data on other metallic substrates, such as Cu, SS, and Nb. The critical current density (J<SUB>c</SUB>) of about 10<SUP>5</SUP>A/cm<SUP>2</SUP> at 5K under 3T is obtained for the MgB<SUB>2</SUB> tape of thickness 2μm. These results suggest that the thick MgB<SUB>2</SUB>/Hastelloy tapes with high J<SUB>c</SUB> values deposited under controlled growth conditions of HPCVD could be useful in high-field applications.
Fabrication of SiC-doped MgB<sub>2</sub> coated conductors by a simple process
Ranot, M.,Jung, S.G.,Seong, W.K.,Lee, N.H.,Kang, W.N.,Joo, J.,Kim, C.J.,Jun, B.H.,Oh, S. North-Holland 2010 Physica. C, Superconductivity Vol.470 No.suppl1
We have fabricated pure and SiC-doped MgB<SUB>2</SUB> thick films on textured Cu (100) tapes with a simple architecture and by an easy process. Firstly, SiC-impurity layers were deposited on Cu tapes at room temperature by using pulsed laser deposition (PLD). Then, MgB<SUB>2</SUB> thick films were grown on the top of SiC/Cu in the temperature range of 460-540<SUP>o</SUP>C by using hybrid physical-chemical vapor deposition (HPCVD). The SiC-doped MgB<SUB>2</SUB>/Cu conductors exhibit critical temperatures ranging between 36 and 38K with superconducting transition width (ΔT<SUB>c</SUB>) of about 0.4-1K. The effects of SiC-doping on the microstructure and critical current density (J<SUB>c</SUB>) of MgB<SUB>2</SUB>/Cu conductors are discussed.
Ranot, Mahipal,Shinde, K.P.,Oh, Y.S.,Kang, S.H.,Jang, S.H.,Hwang, D.Y.,Chung, K.C. The Korea Institute of Applied Superconductivity a 2017 한국초전도저온공학회논문지 Vol.19 No.3
Carbon coating approach is used to prepare carbon-doped $MgB_2$ bulk samples using low-cost naphthalene ($C_{10}H_8$) as a carbon source. The coating of carbon (C) on boron (B) powders was achieved by direct pyrolysis of naphthalene at $120^{\circ}C$ and then the C-coated B powders were mixed well with appropriate amount of Mg by solid state reaction method. X-ray diffraction analysis revealed that there is a noticeable shift in (100) and (110) Bragg reflections towards higher angles, while no shift was observed in (002) reflections for $MgB_2$ doped with carbon. As compared to un-doped $MgB_2$, a systematic enhancement in $J_c(H)$ properties with increasing carbon doping level was observed for naphthalene-derived C-doped $MgB_2$ samples. The substantial enhancement in $J_c$ is most likely due to the incorporation of C into $MgB_2$ lattice and the reduction in crystallite size, as evidenced by the increase in the FWHM values for doped samples.