Y. Kamihara, Y. Kobayashi, R. Takeuchi, M. Matoba
Keio University,
Japan
Keywords: superconductivity, iron-based superconductor, mixed anion layered compounds, MALC, superconducting wires
Summary:
A mixed anion layered compound (MALC) SmFeAsO is a mother compound of iron-based superconductors. F-doped & H-doped SmFeAsO exhibit a superconducting phase with a high upper critical magnetic field and superconducting transition temperatures (Tc). The reported highest Tc of SmFeAsO1-xFx is 58.1 K, which is also the highest among iron-based superconductors. [M. Fujioka, et al., Supercond. Sci. Technol. 26, 085023 (2013).] GdFeAsO1-xFx, which is also an iron-based superconductor, has been reported that the reaction route using GdOF can suppress the amount of second phases compared to the reaction route using GdF3. [H. Shiozawa, Master thesis (Keio Univ. 2014).] In this report, several polycrystalline SmFeAsO1-xFx (nominal x = 0.16) are synthesized using SmOF to achieve high fluorine concentration and high Tc. The nominal x = 0.16 polycrystalline samples were prepared via solid state reaction. The powders of precursors, which are composed of stoichiometric ratios of Sm:Fe:As = 1:2:2 and 1:3:3, were prepared via heat treatment in evacuated silica tube. Powders of SmOF were synthesized by heat-treating a 1:1 mixture of SmF3 and dehydrated Sm2O3. Detailed synthesis procedure of SmFeAsO1-xFx (nominal x = 0.16) will be demonstrated in the conference. The X-ray diffraction patterns of the samples were measured using Rigaku, RINT-2500V, CuKα1 = 0.1541 nm, CuKα2 = 0.1544 nm. From the XRD patterns, the lattice constants and the volume of the unit lattice were obtained by the least-squares method. Volume Vegard rule was used to determine the amount of fluorine substitution. DC electrical resistivity is measured by four-terminal method. The fluorine concentration (x) of a nominal x = 0.16 sample, which were synthesized using SmF3, heat-treated at 950 deg. C for 40 hours, determined by the volume Vegard rule is x = 0.101. x of the other nominal x = 0.16 sample, which were synthesized using SmOF under the same heat treatment conditions, is x = 0.113. Tc of the samples of x = 0.101 and x = 0.113 are 54.7 K and 56.1 K, respectively.