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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.
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Keywords:
- MgB2 /
- Mg(BH4)2 /
- in situ resistance measurement
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图 1 Mg(BH4)2原位烧结制备的MgB2块材
Figure 1. MgB2 bulk fabricated by in situ reaction from Mg(BH4)2
图 2 Mg(BH4)2原位烧结的电阻温度曲线及微分曲线
Figure 2. R-T curve and differential curve for in situ reaction from Mg(BH4)2.
图 3 成相温度与Mg颗粒度之间的拟合曲线
Figure 3. Fitting curve of Mg particle size dependence of phase forming temperature.
图 4 Mg(BH4)2原位烧结制备的MgB2的XRD衍射图
Figure 4. XRD diffraction pattern of MgB2 fabricated by in situ reaction from Mg(BH4)2.
图 5 50 Oe下MgB2样品的抗磁性曲线, 插图为超导转变温度(TC)附近的放大曲线
Figure 5. M-T curve of the MgB2 sample measured under 50 Oe, the inset shows the enlarged curve near TC.
图 6 Mg(BH4)2制备的MgB2的SEM图像 (a) MgB2块材的整体形貌; (b) Mg(BH4)2制备出的MgB2纳米纤维; (c) MgB2纳米纤维生长形成的MgB2晶块
Figure 6. SEM image of MgB2 fabricated by Mg(BH4)2: (a) The morphology of the MgB2 bulk; (b) MgB2 nanofibers generated from Mg(BH4)2; (c) MgB2 grains formed by MgB2 nanofibers.
表 1 不同颗粒度Mg粉对应的MgB2成相温度
Table 1. Phase forming temperature of MgB2 fabricated by different sized Mg powders.
样品编号 1 2 3 4 TPF/K 908 876 842 727 a/μm 100 45 15 0.04 
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[1] Nakamori Y, Miwa K, Ninomiya A, Li H, Ohba N, Towata S I, Zuettel A, Orimo S I 2006 Phys. Rev. B 74 045126
Google Scholar
[2] Voss J, Hummelshøj J S, Łodziana Z, Vegge T 2008 J. Phys.: Condens. Matter 21 012203
Google Scholar
[3] Li H W, Kikuchi K, Nakamori Y, Ohba N, Miwa K, Towata S, Orimo S 2008 Acta Mater. 56 1342
Google Scholar
[4] Chlopek K, Frommen C, Leon A, Zabara O, Fichtner M 2007 J. Mater. Chem. 17 3496
Google Scholar
[5] Fujii H, Ozawa K 2011 Supercond. Sci. Technol. 24 095009
Google Scholar
[6] Luo W H, Huang Z G, Cai X W, Niu R R, Nie R J, Feng Q R, Wang F R, Gan Z Z 2019 Supercond. Sci. Technol. 32 085006
Google Scholar
[7] Yang J Z, Zhang X Z, Zheng J, Song P, Li X G 2010 Scripta Mater. 64 225
Google Scholar
[8] Yang J, Zheng J, Zhang X Z, Li Y Q, Yang R, Feng Q R, Li X G 2010 Chem. Commun. 46 7530
Google Scholar
[9] Chen L P, Zhang C, Wang Y B, Wang Y, Feng Q R, Gan Z Z, Yang J Z, Li X G 2010 Supercond. Sci. Technol. 24 015002
Google Scholar
[10] 张辰, 陈丽萍, 王银博, 吴桃李, 刘文静, 刘雨潇, 薛驰, 冯庆荣 2011 低温 33 97
Google Scholar
Zhang C, Chen L P, Wang Y B, Wu T L, Liu W J, Liu Y X, Xue C, Feng Q R 2011 Chin. J. Low Temp. Phys. 33 97
Google Scholar
[11] 郭峥山, 陈艺灵, 冯庆荣 2012 真空科学与技术学报 32 693
Google Scholar
Guo Z S, Chen Y L, Feng Q R 2012 J. Vac. Sci. Technol. 32 693
Google Scholar
[12] Chen Y L, Liao X B, Cai X Q, Yang C, Guo Z S, Niu R R, Zhang Y, Jia C Y, Feng Q R 2017 Physica C 542 34
Google Scholar
[13] Guo C, Wang H Z, Cai X W, Luo W H, Huang Z G, Zhang Y, Feng Q R, Gan Z Z 2021 Physica C 584 1353863
Google Scholar
[14] Hanada N, Chopek K, Frommen C, Lohstroh W, Fichtner M 2008 J. Mater. Chem. 18 2611
Google Scholar
[15] Zhuang C G, Liu X X, Guo T, Wang B, Li X G, Chen C P, Feng Q R 2007 Supercond. Sci. Technol. 20 1125
Google Scholar
[16] Chen C P, Zhou Z J, Li X G, Xu J, Wang Y H, Gao Z X, Feng Q R 2004 Solid State Commun. 131 275
Google Scholar
[17] DeFouw J D, Quintana J P, Dunand D C 2008 Acta Mater. 56 1680
Google Scholar
[18] 冯庆荣, 陈晋平, 徐军, 王宇昊, 陈鑫 2004 低温 26 46
Google Scholar
Feng Q R, Chen C P, Xu J, Wang Y H, Chen X 2004 Chin. J. Low Temp. Phys. 26 46
Google Scholar
[19] Yamamoto A, Shimoyama J-i, Ueda S, Katsura Y, Horii S, Kishio K 2004 Supercond. Sci. Technol. 18 116
Google Scholar
[20] Yamamoto A, Shimoyama J, Ueda S, Katsura Y, Iwayama I, Horii S, Kishio K 2006 Physica C 445-448 806
Google Scholar
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