Fabrication and characterization of SmO0.7F0.2FeAs bulk with a transition temperature of 56.5 K

The superconductivity of iron-based superconductor SmO0.7F0.2FeAs was investigated. The SmO0.7F0.2FeAs 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 Jc was more than 2.3 × 105 A/cm2 at T = 10 K and H = 9 T, which was calculated by the formula of Jc = 20ΔM/[a(1 a/(3b))]. The upper critical fields, Hc2 ≈ 256 T (T = 0 K), was determined according to the Werthamer-Helfand-Hohenberg formula, indicating that the SmO0.7F0.2FeAs was a superconductor with a very promising application

Detailed Study of the Process of Biomimetic Formation of YBCO Platelets from Nitrate Salts in the Presence of the Biopolymer Dextran and a Molten NaCl Flux

A novel method of achieving microscopic morphological control during the bulk synthesis of the high temperature superconducting ceramic YBa₂Cu₃O₇ (YBCO) has been studied. By incorporating appropriate amounts of the additives dextran (a biopolymer) and NaCl (a high melting point ionic salt) into the synthesis protocol, it is proven possible to engineer high aspect ratio (platelet) growth of the YBCO crystallites together with localized orientational ordering between adjacent densely packed crystallites. In the optimized protocol, both additives are fully consumed during the synthesis by decomposition (dextran) and vaporization (NaCl), leaving phase-pure YBCO as the final synthesis product. The individual effects of the two additives are separately described and their optimal quantities determined. Routes toward improving the yield and increasing the aspect ratio of the resulting crystallites are outlined. The method is likely applicable to the synthesis of other ceramic materials as an alternative to the conventional solid state synthesis route, where a higher degree of connectivity between crystallites is required than can be achieved through sintering