13 results on '"Feng, Qing-rong"'
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2. MgB2 thick film with TC = 40.2 K deposited on sapphire substrate
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Zhang, Kaicheng, Ding, Li-li, Zhuang, Cheng-gang, Chen, Li-ping, Chen*, Chinping., and Feng, Qing-rong
- Subjects
Condensed Matter - Superconductivity - Abstract
We have successfully deposited thick MgB2 film on the (0001) crystalline surface of sapphire by the method of hybrid physical-chemical vapor deposition (HPCVD). The film thickness is about 1.3 micron. It has a dense and interlaced structure. The film surface, shown by SEM, is stacked with MgB2 microcrystals. Transport measurements by the 4-probe technique have demonstrated that its critical temperature is about 40.2 K, with a sharp transition width of 0.15 K. The residual resistivity ratio (RRR) is about 11. By extrapolation, HC2(0) is determined as 13.7 T from the magneto-transport measurement. Also by hysteresis measurement and applying the Bean model, the critical current density is estimated as 5*1010 A/m2 in zero magnetic field. The present work has demonstrated that HPCVD is an effective technique to fabricate the MgB2 thick film with decent superconducting properties. Hence, it is important for the future superconducting application, in particular, as a crucial preliminary stage to fabricate superconducting tape., Comment: 7 pages with 4 figures included, Phys. Stat. Sol. (a) In press
- Published
- 2006
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3. Effect of nanometer-sized B powder on phase formation of polycrystalline MgB2
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An, Ling, Chen, Chinping, Wang, Bo, Zhuang, Cheng-gang, Li, Xing-guo, Zhou, Zeng-jun, and Feng, Qing-rong
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Materials Science - Abstract
The size effect of the raw B powder on the MgB2 phase formation has been studied by the technique of in-situ high temperature resistivity (HT-rT) measurement. The onset temperature, Tonset, and the completion temperature, TPF, of the phase formation are determined directly during the ongoing thermal process. These two temperatures, Tonset and TPF of the sample synthesized using nanometer B and Mg powders (NanoB-MgB2) are 440 C and 490 C, respectively, the same as those of the sample using micrometer B and nanometer Mg powders (MicroB-MgB2). This indicates that the phase formation temperature of MgB2 do not depend on the B powder size. On the other hand, the upper limit of the sintering temperature, TN, above which the sample loses superconductivity, is below 750 C for NanoB-MgB2, much lower than 980 C for the MgB2 prepared using micron-sized B powder and millimeter sized Mg powder (DM-MgB2). In comparison with the sample directly sintered at 650 C < TN, an interesting, irreversible transformation in the crystal structure of the MgB2 phase was observed with the sample going through the stages of initial sintering at 750 C, then re-sintering at 650 C in an Mg-rich environment after the processes of regrinding and pressing. Possible explanation of the observed properties is discussed., Comment: 7 pages with 4 figures included
- Published
- 2004
4. MgB2 thick film grown on Stainless steel substrate with ductility
- Author
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Feng, Qing-rong, Chen, Chinping, Lu, Ying, Zia, Zhang, Guo, Jing-pu, Wang, Xiao-nan, Zhu, Meng, Xu, Jun, and Wang, Yong-zhong
- Subjects
Condensed Matter - Superconductivity - Abstract
MgB2 thick film was synthesized on the stainless steel substrate by the technique of hybrid physical-chemical vapor deposition (HPCVD), using Mg ingot and B2H6 as the raw materials. The film thickness is about 10 microns. The scanning electron microscope (SEM) images reveal that it is consisting of highly dense MgB2 crystals with the size ranging from 0.2 to 3 microns. The superconducting transition occurs at 38 K (Tc, onset) and ends at 27 K (Tc, zero), giving the transition width of 11 K. The fabricated film exhibits high ductility and remains attached to the substrate after it was bent to a curvature of about 200 microns., Comment: 4 pages, Proceedings of SPIE, the 5th International Conference on Thin Film Physics and Applications 2004
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- 2004
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5. Phase formation of polycrystalline MgB2 at low temperature using nanometer Mg powder
- Author
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Chen, Chinping, Zhou, Zeng-jun, Li, Xing-guo, Xu, Jun, Wang, Yu-hao, Wang, Yong-zhong, and Feng, Qing-rong
- Subjects
Condensed Matter - Superconductivity - Abstract
The MgB2 superconductor synthesized in a flowing argon atmosphere using nanometer magnesium powder as the raw materials, denoted as Nano-MgB2, has been studied by the technique of in-situ high temperature resistance measurement (HT-RT measurement). The MgB2 phase is identified to form within the temperature range of 430 to 490 C, which is much lower than that with the MgB2 sample fabricated in the same gas environment using the micron-sized magnesium powder, denoted as Micro-MgB2, reported previously. The sample density of the Nano-MgB2 reaches 1.7 g/cm3 with a crystal porosity structure less than a micrometer, as determined by the scanning electron microscope (SEM) images, while the Micro-MgB2 has a much more porous structure with corresponding density of 1.0 g/cm3. This indicates that the Mg raw particle size, besides the sintering temperature, is a crucial factor for the formation of high density MgB2 sample, even at the temperature much lower than that of the Mg melting, 650 C. The X-ray diffraction (XRD) pattern shows a good MgB2 phase with small amount of MgO and Mg and the transition temperature, TC, of the Nano-MgB2 was determined as 39 K by the temperature dependent magnetization measurement (M-T), indicating the existence of a good superconducting property., Comment: 10 pages, 4 figure, Solid State Communication
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- 2004
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6. Thick MgB2 film with (101) oriented micro-crystals
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Chen, Chinping, Wang, Xinfeng, Lu, Ying, Jia, Zhang, Guo, Jing-pu, Wang, Xiao-nan, Zhu, Meng, Xu, Xiangyu, Xu, Jun, and Feng, Qing-rong
- Subjects
Condensed Matter - Superconductivity - Abstract
Very thick, ~ 40 $\mu$m, clean, and highly textured MgB2 film was effectively grown on an Al2O3 substrate. The fabrication technique is by the hybrid physical-chemical vapor deposition (HPCVD) using B2H6 gas and Mg ingot as the sources. The X-ray diffraction (XRD) analysis shows a highly (101)-oriented MgB2 crystal structure without any impurity detected. There is no signal from the substrate in the XRD spectrum, indicating that the film thickness exceeds the X-ray penetration length. Scanning electron microscopy (SEM) reveals that the film is composed of highly-packed MgB2 micro-crystals with a uniform size distribution of about 2 $\mu$m in diameter and 0.2 $\mu$m in thickness. According to the compositional analysis of energy-dispersive X-ray spectroscopy (EDX), no oxygen, hence no MgO, exists in the textured film, consistent with the XRD result. Also, the transport properties are similar to those of a single crystal, indicating a clean film of good crystallite. The zero field transition temperatures are determined as TC(onset) = 39.2 K and TC(zero) = 38.4 K, giving a sharp transition typical of a clean sample. The residual resistivity ratio (RRR) is determined as 6.4 and the magnetoreisitance (MR) is about 28 % at 40 K under the applied field of 9 T, which are similar to those of a single crystal. The zero temperature upper critical field, HC2(0), is extrapolated as 19 T from the TC(onset) at applied field up to 9 T., Comment: 10 pages, 4 figures
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- 2004
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7. Study on the formation of MgB2 phase
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Feng, Qing-rong, Chen, Chinping, Xu, Jun, Kong, Ling-wen, Chen, Xiu, Wang, Yong-zhong, and Gao, Zheng-xiang
- Subjects
Condensed Matter - Abstract
We report the study of the polycrystalline MgB2 phase formation during the fabrication processes. Three major phases are identified in different sintering temperature ranges according to the corresponding superconducting properties and the crystalization conditions. The optimum fabrication parameters are obtained for the MgB2 superconducting phase formation., Comment: 10 pages, figures included
- Published
- 2003
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8. In situ resistance analysis of MgB2 formation process from Mg(BH4)2
- Author
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Luo Wen-Hao, Huang Zi-Geng, Cai Xin-Wei, Feng Qing-rong, Gan Zi-Zhao, and Guo Chen
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In situ ,Materials science ,Chemical engineering ,Scientific method ,General Physics and Astronomy - Abstract
Mg(BH4)2 was previously studied as a promising hydrogen storage material, because of its high gravimetric storage capacities for hydrogen and suitable thermodynamic properties. Mg(BH4)2 began to decompose at about 300 ℃, and formed MgB2 at the end of hydrogen desorption process with the weight content of 14.9% of hydrogen lost. Aside from the prominent hydrogen storage property, the decomposition process from Mg(BH4)2 to MgB2 can be a potential method for fabricating superconducting MgB2 at a low sintering temperature. In this paper, MgB2 bulk was prepared by an in-situ reaction, using the Mg(BH4)2 pressed block as a precursor. The resistance change of the sample was monitored during the Mg(BH4)2 decomposition process and the resistance-temperature (R-T) curve of this process was recorded. Phase of MgH2, Mg and B were formed as the block slowly release its hydrogen before MgB2 occurred. According to the R-T curve, the phase formation of MgB2 started in a relatively low temperature of 410 ℃. Because MgB2 was critically formed by Mg and B derived from Mg(BH4)2, we can compare our formation temperature with previous study on MgB2 prepared by Mg and B in different particle size. The fitting result indicated that the particle size of Mg and B harvest from Mg(BH4)2 decomposition was only 3.4 nm on average. The nearly atomic level mixture of Mg and B resulted in a high chemical reactivity, which was the main reason for low sintering temperature. X-ray diffraction results showed that the purity of MgB2 was 95.2%, and the size of MgB2 grains was 10–18 nm. SEM images showed that the MgB2 bulk had a porous structure and poor connectivity, which was caused by large amount the hydrogen release during the decomposition. MgB2 nanofibers can also be observed inside the bulk. In the superconductivity test, the superconducting transition temperature of the bulk was 35 K. After all, such in situ method to fabricate MgB2 showed a great advantage in some aspects, as its low-cost precursors, low sintering temperature, small grain-size and high superconducting transition temperature in the formed MgB2, which have the potential in industrial scale fabrication of MgB2 bulks and wires.
- Published
- 2021
9. Degradation of MgB 2 Ultrathin Films Under Different Environmental Conditions
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Wang, Da, primary, Zhang, Chen, additional, Zhang, Jun, additional, Zhang, Yan, additional, Feng, Qing-Rong, additional, Wang, Yue, additional, and Gan, Zi-Zhao, additional
- Published
- 2015
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10. Fabrication of superconducting nanowires from ultrathin MgB2 films via focused ion beam milling
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Zhang, Chen, primary, Wang, Da, additional, Liu, Zheng-Hao, additional, Zhang, Yan, additional, Ma, Ping, additional, Feng, Qing-Rong, additional, Wang, Yue, additional, and Gan, Zi-Zhao, additional
- Published
- 2015
- Full Text
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11. Study on single crystal MgB2 nanosheets grown by hybrid physical-chemical vapor deposition
- Author
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Ma Ping, Wang Yue, Zhang Yan, and Feng Qing-Rong
- Subjects
Materials science ,Hybrid physical-chemical vapor deposition ,Chemical engineering ,General Physics and Astronomy ,Single crystal - Abstract
This report is focused on the MgB2 nanosheets which have a hexagonal single crystal structure with variable thickness and different radial dimensions. The nanosheets are fabricated by hybird physical-chemical vapor deposition for the first time, as far as we know, and meanwhile they can be site-specific transferred so as to make physical properties measurement. Results of electrical and magnetic measurements indicate that the nanosheets is superconductive with a Tconset=38 K, Tc (0)=33 K. The images of scanning electrical microscope show that the nanosheets have a nanoscale thickness and have not only a large scale in wildth from several microns to hundreds of microns but also a flat cleaning surface. The selected area electrical diffraction data is consistent with the early report of MgB2 diffraction. According to those results, the single crystal nanosheets with high quality can be surely indentified as MgB2. It suggests a new technique for MgB2 single crystal fabrication, and a zero electrical behavior is observed in nanoscale single crystal MgB2. This could be a new opportunity to make a right material for the afterward research such as flux vortices, nanoscale mechanical properties.
- Published
- 2014
12. The effects of Ti ion-irradiation on critical current and flux pinning in MgB2 thin film
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Feng Qing-Rong, Wang Yin-Bo, and Xue Chi
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Flux pinning ,Materials science ,Condensed matter physics ,General Physics and Astronomy ,Irradiation ,Critical current ,Thin film ,Ion - Abstract
High-quality MgB2 films are fabricated via hybrid physical-chemical vapor deposition (HPCVD) and irradiated by Ti ions. Compared with the unirradiated film, the Ti-irradiated MgB2 film shows a high critical current density (Jc) in magnetic field and also a high upper critical field (Hc2), while the superconducting transition temperature (Tc) does not decrease significantly. The Ti-irradiated film with a best fluence at 1 1013/cm2 shows a high Jc of 1.72 105 A/cm2 in 4 T perpendicular field at a temperature of 5 K and a moderately decreased Tc at 39.9 K.
- Published
- 2012
13. Properties of MgB2 ultra-thin films grown by hybrid physical-chemical vapor deposition
- Author
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Huang Xu, Wang Ya-Zhou, Feng Qing-Rong, and Sun Xuan
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Residual resistivity ,Materials science ,Hybrid physical-chemical vapor deposition ,Analytical chemistry ,General Physics and Astronomy ,Deposition (phase transition) ,Nanotechnology ,Chemical vapor deposition ,Thin film ,Epitaxy ,Critical field ,Volumetric flow rate - Abstract
We fabricate MgB 2 ultra-thin films via hybrid physical-chemical vapor deposition technique. Under the same background pressure, the same H 2 flow rate, by changing B 2 H 6 flow rate and deposition time, we fabricate a series of ultra-thin films with thickness ranging from 5 nm to 80 nm. These films grow on SiC substrate, and are all c -axis epitaxial. We study the Volmer-Weber mode in the film formation. As the thickness increases, critical transition temperature T c (0) also increases and the residual resistivity decreases. Especially, a very high T c (0) ≈ 32.8 K for the 7.5 nm film, and T c (0) ≈ 36.5 K, low residual resistivity ρ (42 K)≈ 17.7 μΩcm, and extremely high critical current density J c (0 T,4 K) ≈ 10 7 A/cm 2 , upper critical field H c2 (0) for 10 nm film are achieved. Moreover, by optimizing the H 2 flow rate, we obtain relatively smooth surface of the 10 nm epitaxial film, with a root-mean-square roughness of 0.731 nm, which makes them well qualified for device applications.
- Published
- 2011
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