不同包套石墨烯掺杂MgB_2超导线材的性能
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摘要
分别采用Fe和Nb作为阻隔层包套材料,通过原位粉末装管法(in-situ PIT)制备出石墨烯掺杂的MgB_2/Fe(Nb)/Cu线材和Nb包套未掺杂的MgB_2单芯线材。线材在高纯氩气保护下、670～800℃保温2 h热处理。XRD结果显示,670℃热处理的线材其主相均为MgB_2超导相,其中Fe包套线材中含有Fe_2B杂相。3种线材的微观结构显示,未掺杂线材基体中的孔洞相对较大,而石墨烯掺杂的Fe、Nb包套线材基体中的孔洞相对较小。线材样品的拉伸结果显示,热处理前由于加工硬化,3种线材的拉伸应变值远远低于热处理后的拉伸应变值,其中铁包套线材的硬化最为严重,但无论是否热处理,Fe包套样品的强度都是最大的。样品的四引线法传输性能测试显示,670℃热处理Nb包套掺杂线材的临界电流密度(J_c)在4.2 K,2 T、4 T、6 T范围内均高于Fe包套掺杂线材的J_c,石墨烯掺杂线材(Nb、Fe包套)在2 T具有更好的传输性能,Nb包套掺杂线材的J_c最高可达到4.59×10~5 A/cm~2。当外加磁场大于4 T后,2种包套的掺杂线材的J_c均低于未掺杂的线材,Fe包套样品的超导性能降低更大,显示其掺杂未全部进入晶格,导致其在高场下磁通钉扎作用下降。
Single filament MgB_2/Fe(Nb)/Cu wires with or without graphene doping, using Fe and Nb as sheath, were fabricated by the in-situ PIT method. The heat treatment of sample was at 670～800 ℃ for 2 h under high purity Ar atmosphere. X-ray diffraction pattern shows the main phase of the wires with heat treatment at 670 ℃ is MgB_2 phase, except partial Fe_2B impurity phase in Fe sheathed MgB_2 wires. Microstructure analysis shows the hole between crystal grains in the wire without doping is bigger than that of Fe or Nb sheathed MgB_2 wire doped with graphene. Stress-strain test results show that the tensile strain values for the wire before heat treatment are lower than those of wires after heat treatment obviously. Hardenability of Fe sheathed wires is more sharpness. The strength is the maximum for Fe sheathed wires with or without heat treatment. Four probe transfer measurement properties show that the critical current density J_c of Nb sheathed wire heat treatment at 670 ℃ is higher than that of Fe sheathed wire at 4.2 K with the field of 2, 4 and 6 T. Nb and Fe sheathed MgB_2 wires doped with graphene possess better transfer performance at 2 T. The J_c value at 2 T reaches 4.59×10~5 A/cm~2 for Nb sheathed wires. When the field is higher than 4 T, the J_c values of Nb and Fe sheathed MgB_2 wires doped with graphene are lower than that of undoped wire. The transfer property of Fe sheathed wires reduce faster than those of other samples. This indicates that the dopants incompletely enter the crystal structure, leading to the reduced flux pinning function at high field.
Single filament MgB_2/Fe(Nb)/Cu wires with or without graphene doping, using Fe and Nb as sheath, were fabricated by the in-situ PIT method. The heat treatment of sample was at 670～800 ℃ for 2 h under high purity Ar atmosphere. X-ray diffraction pattern shows the main phase of the wires with heat treatment at 670 ℃ is MgB_2 phase, except partial Fe_2B impurity phase in Fe sheathed MgB_2 wires. Microstructure analysis shows the hole between crystal grains in the wire without doping is bigger than that of Fe or Nb sheathed MgB_2 wire doped with graphene. Stress-strain test results show that the tensile strain values for the wire before heat treatment are lower than those of wires after heat treatment obviously. Hardenability of Fe sheathed wires is more sharpness. The strength is the maximum for Fe sheathed wires with or without heat treatment. Four probe transfer measurement properties show that the critical current density J_c of Nb sheathed wire heat treatment at 670 ℃ is higher than that of Fe sheathed wire at 4.2 K with the field of 2, 4 and 6 T. Nb and Fe sheathed MgB_2 wires doped with graphene possess better transfer performance at 2 T. The J_c value at 2 T reaches 4.59×10~5 A/cm~2 for Nb sheathed wires. When the field is higher than 4 T, the J_c values of Nb and Fe sheathed MgB_2 wires doped with graphene are lower than that of undoped wire. The transfer property of Fe sheathed wires reduce faster than those of other samples. This indicates that the dopants incompletely enter the crystal structure, leading to the reduced flux pinning function at high field.
引文
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[3]Ková?P,Hu?ek I,Dobro?ka E et al.Supercond Sci Technol[J],2008,21:015 004
[4]Ková?P,Birajdar B,Hu?ek I et al.Supercond Sci Technol[J],2008,21:045 011
[5]Kumar R G A,Visnod K,Varghese N et al.Supercond Sci Technol[J],2007,20:222
[6]Fang H,Gijavanekar P,Zhou Y X et al.IEEE T Appl Supercon[J],2005,15(2):3215
[7]Kulich M,Ková?P,Weber H W et al.Supercond Sci Technol[J],2011,24:065 025
[8]Gajda D,Morawski A,Zaleski A J et al.J Appl Phys[J],2016,120:113 901
[9]Ma Y W,Kumakura H,Matsumoto A et al.Supercond Sci Technol[J],2003,16(8):852
[10]Sudesh N K,Das S,Bernhard C et al.Supercond Sci Technol[J],2013,26(9):095 008
[11]Wang Qingyang(王庆阳),Yan Guo(闫果),Liu Guoqing(刘国庆)et al.Rare Metal Materials and Engineering(稀有金属材料与工程)[J],2007,36(8):1440
[12]Liu H R,Yang F,Jing L H et al.J Supercond Nov Magn[J],2018,31(4):1053
[13]Liu Guoqing(刘国庆),Yan Guo(闫果),Wang Qingyang(王庆阳)et al.Rare Metal Materials and Engineering(稀有金属材料与工程)[J],2008,37(S4):444
[14]Ková?P,Hu?ek I,Skakalova V et al.Supercond Sci Technol[J],2007,20:105
[15]Tang S P,Wang D L,Zhang X P et al.J Supercond Nov Magn[J],2014,27(12):2699
[16]Avdeev M,Jorgensen J D,Ribeiro R A et al.Physica C[J],2003,387(3-4):301
[17]Balaselvi S J,Gayathri N,Bharathi A et al.Supercond Sci Technol[J],2004,17:1401
[18]Wang Qingyang(王庆阳),Yan Guo(闫果),Liu Guoqing(刘国庆)et al.Chinese Journal of Low Temperature(低温物理学报)[J],2010,32(2):133
[19]Susner M A,Bohnenstiehl S D,Dregia S A et al.Appl Phys Lett[J],2014,104(16):162 603
[20]Wang Qingyang(王庆阳),Zhang Pingxiang(张平祥),Yan Guo(闫果)et al.Rare Metal Materials and Engineering(稀有金属材料与工程)[J],2013,42(5):881
[21]Sun Y Y,Liu G Q,Qi M et al.Physica C[J],2013,485:24