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首页> 外文期刊>The Physics of Metals and Metallography >Studying Nanocrystalline Superconducting Nb_3Sn Layers in Nb/Cu-Sn Composites of Various Design Using NMR and Magnetic Susceptibility Methods
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Studying Nanocrystalline Superconducting Nb_3Sn Layers in Nb/Cu-Sn Composites of Various Design Using NMR and Magnetic Susceptibility Methods

机译：利用核磁共振和磁化率方法研究各种设计的Nb / Cu-Sn复合材料中的纳米超导Nb_3Sn层

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The paper presents the results of measurements of the temperature dependence of the shape of the NMR lines of ~(93)Nb and of the real part of the dynamic magnetic ac susceptibility chi'(T) for multifilamentary superconducting Nb_3Sn-based composites with various geometry of niobium filaments (ordinary cylindrical, paired cylindrical, and ringlike (tubular)) produced by the bronze technology. In all the composites studied, a superconducting (SC) transition was observed in diffusional Nb_3Sn layers at T_c approx 17 K. Its width is DELTA T_c approx = 3 K and is independent of the composite design. The difference in the absolute value of chi'(T) in the composites of ordinary assembly and with paired filaments is less by a factor of 1.5 than that of a composite with ring filaments. In the experimental NMR spectra of ~(93)Nb, subspectra of different intensities have been distinguished, whose number is three in ordinary assemblies and in assemblies with paired filaments, and two in composites with ring filaments. Estimates of the intensities of each subspectrum in each experimental spectrum of the composites studied has been correlated with a definite diffusional layer of Nb_3Sn; thus, the number of grains of a corresponding layer in each composite has been estimated. In addition, it has been established that in the first two composites the shape of the NMR line of ~(93)Nb is asymmetric, which indicates the existence of an anisot-ropy of the Knight shift in Nb_3Sn layers in both the normal and superconducting states, whereas in the composite with ring filaments the line is symmetric and the Knight shift is isotropic. The magnitude of the anisotropic Knight shift in composites with isolated and paired cylindrical filaments is ~(93)K_(an) approx = 0.02 percent. The anisotropy in them appears to be due to the different character and magnitude of interaction of grains of the Nb_3Sn layers with the bronze matrix and the residual Nb, which leads to different shifts of the subspectrum frequencies and, correspondingly, to the shape asymmetry of the NMR line of ~(93)Nb. At the same time, in a composite with ring filaments the interaction of the Nb_3Sn layer with the bronze matrix occurs on both sides, is, apparently, of the same character and is compensated in magnitude. In this case, in the first two composites the tin distribution across the diffusional layers of Nb_3Sn is nonuniform and a significant deviation from the stoichiometric composition is observed.
机译：本文给出了多种几何结构的多丝超导Nb_3Sn基复合材料的〜（93）Nb NMR线形状和动态磁ac磁化率chi'（T）实部的温度依赖性测量结果青铜技术生产的铌丝（普通圆柱形，成对圆柱形和环状（管状））。在所有研究的复合材料中，在扩散Nb_3Sn层中的T_c约为17 K处均观察到超导（SC）过渡。其宽度为DELTA T_c约为3 K，并且与复合材料设计无关。普通组件和成对长丝复合材料中chi'（T）的绝对值差异比带环形长丝的复合材料中的chi'（T）绝对值小1.5倍。在〜（93）Nb的实验NMR光谱中，已区分出不同强度的亚谱，在普通组件和成对的长丝组件中，该子光谱的数目为3，而在具有环形长丝的复合物中，其数目为2。在所研究的复合材料的每个实验光谱中，每个子谱的强度估计值都与Nb_3Sn的确定扩散层相关。因此，已经估计了每种复合物中相应层的晶粒数。此外，已确定在前两个复合物中〜（93）Nb的NMR线的形状是不对称的，这表明在正常和超导Nb_3Sn层中存在奈特位移的各向异性状态，而在具有环形长丝的复合材料中，线是对称的，奈特位移是各向同性的。具有孤立的和成对的圆柱丝的复合材料的各向异性Knight位移的大小约为〜（93）K_（an）= 0.02％。它们中的各向异性似乎是由于Nb_3Sn层的晶粒与青铜基体和残余Nb相互作用的特性和幅度不同，这导致了次频谱频率的不同偏移，并相应地导致了Nb_3Sn层的形状不对称。 〜（93）Nb的NMR线。同时，在具有环形细丝的复合材料中，Nb_3Sn层与青铜基体的相互作用在两侧均发生，显然具有相同的特性，并且在大小上得到补偿。在这种情况下，在前两个复合物中，锡在Nb_3Sn扩散层上的分布不均匀，并且观察到与化学计量组成的明显偏差。

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