MgB2/Fe带材Jc的各向异性及MgB2芯织构和成分不均一性的研究

本文研究了在不同磁场方向和温度下非原位Fe包套MgB2单芯带Jc的各向异性,通过对各种工艺条件下带材中MgB2芯的X-ray衍射图进行拟合分析和计算,比较了MgB2芯在Fe-MgB2界面和中心处的织构度和成份不均一性.研究发现带材Jc的各向异性受初始粉末颗粒尺寸的影响.由于受套管材料强度和形变加工工艺的影响,MgB2芯在Fe-MgB2界面处比在中心处有较强的织构.在MgB2-Fe的界面处,700℃淬火样品的X-ray衍射图中发现了由中间相Fe23B6生成的金属间化合物Fe2B.另外还研究了MgB4和MgO等主要杂质相的形成原因.     

Electronically ‘atypical’ a 15-type compounds based on chromium and molybdenum

The superconducting transition temperature has been investigated as a function of composition and degree of long-range order in a number of binary and ternary A 15-type phases on Cr and Mo. It is concluded that these compounds are unlike the typical Nb- or V- based phases with the same structure. The maximum T_c does usually not occur at the ideal composition. Nevertheless, a correlation has been found between T_c and the degree of order.     

Mechanism of enhancement in electromagnetic properties of MgB2 by Nano SiC doping

A comparative study of pure, SiC, and C doped MgB2 wires has revealed that the SiC doping allowed C substitution and MgB2 formation to take place simultaneously at low temperatures. C substitution enhances H_{c2}, while the defects, small grain size, and nanoinclusions induced by C incorporation and low-temperature processing are responsible for the improvement in J_{c}. The irreversibility field (H_{irr}) for the SiC doped sample reached the benchmarking value of 10 T at 20 K, exceeding that of NbTi at 4.2 K. This dual reaction model also enables us to predict desirable dopants for enhancing the performance properties of MgB2.     

Supraconductivite et chaleur specifique dans les alliages A15 a base de titane

Experimental data on the superconducting transition temperature, and low temperature specific heat, together with X-ray investigations, are reported for binary and pseudo-binary compounds of Ti with the A 15-type structure. A “true” relative maximum of the coefficient of the electronic specific heat, γ, as well as the superconducting transition temperature, T_c, occurs in the Ti₃Ir_?xPt_x system near x = 0.2. Ti₃Ir_0.8Pt_0.2 shows the lowest Debye temperature, θ₀ , of all A 15-type compounds known to date. The anomalous temperature dependence of the lattice specific heat may be reproduced by a model phonon spectrum similar to that of Nb₃Sn.