PIT(powder in tube)法制备了MgB2超导材料;用Campbell法测量了样品的外加交流磁场bac与磁通渗透深度λ′的关系,并计算得到样品在外磁场中的临界电流密度;讨论了bac-λ′,曲线误差形成的原因和选取曲线平稳部分为计算有效段原则;Campbell法测量考虑了样品的整体结构影响电流的特性,得到的结果更切合超导材料的实际临界电流密度。
The superconductivity of iron-based superconductor SmO 0.7 F 0.2 FeAs was investigated. The SmO 0.7 F 0.2 FeAs sample was prepared by the two-step solid-state reaction method. The onset resistivity transition temperature is as high as 56.5 K. X-ray diffraction （XRD） results show that the lattice parameters a and c are 0.39261 and 0.84751 nm, respectively. Furthermore, the global J c was more than 2.3 × 10 5 A/cm 2 at T = 10 K and H = 9 T, which was calculated by the formula of J c = 20ΔM/[a（1-a/（3b））]. The upper critical fields, H c2 ≈ 256 T （T = 0 K）, was determined according to the Werthamer-Helfand-Hohenberg formula, indicating that the SmO 0.7 F 0.2 FeAs was a superconductor with a very promising application.
We have studied the adsorption of elemental S on the surfaces of NiW alloy substrates where elementary sulfur was used as sulfur source. Compared with those previous investigations which used H2S as the sulfur source and operated in an ultra-high vacuum chamber, we used elemental sulfur as the sulfur source which does not need an ultra-high vacuum chamber but Ar-H protection atmosphere in the process of sulfuration. After sulfuration, epitaxial LZO buffer layers were deposited on these substrates directly. The samples were investigated by means of AFM, XPS, SEM and XRD in this study. The results show that after sulfuration, S forms a c (2×2) structure at a coverage of 0.5 ML, in agreement with previous results, representing the effectiveness of elemental sulfur during the sulfuration process. The c (2×2)-S superstructure on the surface of the NiW substrates has optimized the La2Zr2O7(LZO) buffer layer texture.
Wang Xue1, 2, Li Chengshan2, Yu Zeming2, Zheng Huiling2, Ji Yongbin2, Chen Zewen 1, 2, Fan Zhanguo 1 1Northeastern University, Shenyang 110004, China
