The high cost of using the niobium(Nb)barrier for manufacturing magnesium diboride(MgB2)mono-and multi-filamentary wires for large-scale applications has become one of the barriers to replacing current commercial niob...The high cost of using the niobium(Nb)barrier for manufacturing magnesium diboride(MgB2)mono-and multi-filamentary wires for large-scale applications has become one of the barriers to replacing current commercial niobium-titanium superconductors.The potential of replacing the Nb barrier with a low-cost iron(Fe)barrier for multifilament MgB2 superconducting wires is investigated in this manuscript.Therefore,MgB2 wires with Fe barrier sintered with different temperatures are studied(from 650°C to 900°C for 1 h)to investigate the non-superconducting reaction phase of Fe-B.Their superconducting performance including engineering critical current density(Je)and n-value are tested at 4.2 K in various external magnetic fields.The best sample sintered at 650°C for 1 h has achieved a Je value of 3.64×10^(4) A cm^(−2) and an n-value of 61 in 2 T magnetic field due to the reduced formation of Fe2B,better grain connectivity and homogenous microstructure.For microstructural analysis,the focused ion beam(FIB)is utilised for the first time to acquire three-dimensional microstructures and elemental mappings of the interface between the Fe barrier and MgB2 core of different wires.The results have shown that if the sintering temperature can be controlled properly,the Je and n-value of the wire are still acceptable for magnet applications.The formation of Fe2B is identified along the edge of MgB2,as the temperature increases,the content of Fe2B also increases which causes the degradation in the performance of wires.展开更多
用PIT(powder in tube)法在不同条件下制备MgB2样品,通过X射线衍射、扫描电子显微镜(SEM)对不同参数下制备样品的成分和微观结构进行了表征;利用Campbell法检测样品的bac-λ′关系,求得样品的超导临界转变电流密度Jc;由样品的Jc结合形...用PIT(powder in tube)法在不同条件下制备MgB2样品,通过X射线衍射、扫描电子显微镜(SEM)对不同参数下制备样品的成分和微观结构进行了表征;利用Campbell法检测样品的bac-λ′关系,求得样品的超导临界转变电流密度Jc;由样品的Jc结合形貌与相成分对比分析,结果表明:长时间烧结,晶粒较大,利于导电,但缺乏钉扎作用,在外磁场下超导电流减小。长时间烧结,晶界间氧化层增厚,超导电流密度减小。展开更多
The electron transport of linear atomic chain trodes was investigated by using the density Green＇s function method. We have calculated of MgB2 sandwiched between Au（100） elecfunctional theory with the non-equilibri...The electron transport of linear atomic chain trodes was investigated by using the density Green＇s function method. We have calculated of MgB2 sandwiched between Au（100） elecfunctional theory with the non-equilibrium the corresponding cohesion energy and conductance of junctions in different distance. It is found that, at the equilibrium position, the Au-B bond-length is 1.90 A, the B-Mg bond-length is 2.22 A, and the equilibrium conductance is 0.51G0 （Go=2e^2/h）. The transport channel is almost formed by the π antibonding orbitals, which was made up of the Px and Py orbital electrons of B and Mg atoms. In the voltage range of -1.5 to 1.5 V, the junctions show the metallic behaviors. When the voltage is larger than 1.5 V, the current decreases gradually and then negative differential resistance appears almost symmetrically on both positive and negative bias.展开更多
The elastic constants of superconducting MgB2 are calculated using a molecular dynamics method (MD)with shell model. The lattice parameters, five independent elastic constants, equations of state (EOS), Debye temperat...The elastic constants of superconducting MgB2 are calculated using a molecular dynamics method (MD)with shell model. The lattice parameters, five independent elastic constants, equations of state (EOS), Debye temperature, and bulk modulus of MgB2 are obtained. Meanwhile, the dependence of the bulk modulus B, the lattice parameters a and c, and the unit cell volume V on the applied pressure are presented. It is demonstrated that the method introduced here can well reproduce the experimental results with a reasonable accuracy.展开更多
基金support from the Australian Research Council(ARC)Linkage Project(LP200200689).
文摘The high cost of using the niobium(Nb)barrier for manufacturing magnesium diboride(MgB2)mono-and multi-filamentary wires for large-scale applications has become one of the barriers to replacing current commercial niobium-titanium superconductors.The potential of replacing the Nb barrier with a low-cost iron(Fe)barrier for multifilament MgB2 superconducting wires is investigated in this manuscript.Therefore,MgB2 wires with Fe barrier sintered with different temperatures are studied(from 650°C to 900°C for 1 h)to investigate the non-superconducting reaction phase of Fe-B.Their superconducting performance including engineering critical current density(Je)and n-value are tested at 4.2 K in various external magnetic fields.The best sample sintered at 650°C for 1 h has achieved a Je value of 3.64×10^(4) A cm^(−2) and an n-value of 61 in 2 T magnetic field due to the reduced formation of Fe2B,better grain connectivity and homogenous microstructure.For microstructural analysis,the focused ion beam(FIB)is utilised for the first time to acquire three-dimensional microstructures and elemental mappings of the interface between the Fe barrier and MgB2 core of different wires.The results have shown that if the sintering temperature can be controlled properly,the Je and n-value of the wire are still acceptable for magnet applications.The formation of Fe2B is identified along the edge of MgB2,as the temperature increases,the content of Fe2B also increases which causes the degradation in the performance of wires.
文摘用PIT(powder in tube)法在不同条件下制备MgB2样品,通过X射线衍射、扫描电子显微镜(SEM)对不同参数下制备样品的成分和微观结构进行了表征;利用Campbell法检测样品的bac-λ′关系,求得样品的超导临界转变电流密度Jc;由样品的Jc结合形貌与相成分对比分析,结果表明:长时间烧结,晶粒较大,利于导电,但缺乏钉扎作用,在外磁场下超导电流减小。长时间烧结,晶界间氧化层增厚,超导电流密度减小。
基金V. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.11174214 and No.11204192）, the Research Project of Education Department in Sichuan Province （No.13ZB0207）, and Scientific Research Project of Yibin University （No.2013YY05）.
文摘The electron transport of linear atomic chain trodes was investigated by using the density Green＇s function method. We have calculated of MgB2 sandwiched between Au（100） elecfunctional theory with the non-equilibrium the corresponding cohesion energy and conductance of junctions in different distance. It is found that, at the equilibrium position, the Au-B bond-length is 1.90 A, the B-Mg bond-length is 2.22 A, and the equilibrium conductance is 0.51G0 （Go=2e^2/h）. The transport channel is almost formed by the π antibonding orbitals, which was made up of the Px and Py orbital electrons of B and Mg atoms. In the voltage range of -1.5 to 1.5 V, the junctions show the metallic behaviors. When the voltage is larger than 1.5 V, the current decreases gradually and then negative differential resistance appears almost symmetrically on both positive and negative bias.
基金中国科学院资助项目，Scientific Research Foundation for Returned Overseas Chinese Scholars，Ministry of Education of China
文摘The elastic constants of superconducting MgB2 are calculated using a molecular dynamics method (MD)with shell model. The lattice parameters, five independent elastic constants, equations of state (EOS), Debye temperature, and bulk modulus of MgB2 are obtained. Meanwhile, the dependence of the bulk modulus B, the lattice parameters a and c, and the unit cell volume V on the applied pressure are presented. It is demonstrated that the method introduced here can well reproduce the experimental results with a reasonable accuracy.
