Masaya Fujioka

Evolution of superconductivity in LaO1−xFxBiS2 prepared by high-pressure technique

Novel BiS2-based superconductors LaO1-xFxBiS2 prepared by the high pressure synthesis technique were systematically studied. It was found that the high pressure annealing strongly the lattice as compared to the LaO1-xFxBiS2 samples prepared by conventional solid state reaction at ambient pressure. Bulk superconductivity was observed within a wide F-concentration range of x = 0.2 ~ 0.7. On the basis of those results, we have established a phase diagram of LaO1-xFxBiS2.

Phase diagram and superconductivity at 58.1 K in α-FeAs-free SmFeAsO1−xFx

The phase diagram of SmFeAsO1−xFx in terms of x is exhibited in this study. Specimens of SmFeAsO1−xFx from x = 0 to x = 0.3 were prepared by low-temperature sintering with slow cooling. The low-temperature sintering suppresses the formation of the amorphous FeAs, which is inevitably produced as an impurity when using high-temperature sintering. Moreover, slow cooling is effective in obtaining a high fluorine concentration. The compositional change from feedstock composition is quite small after this synthesis. We can reproducibly observe a record superconducting transition for an iron-based superconductor at 58.1 K. This achievement of a high superconducting transition is due to the success in substituting a large amount of fluorine. A shrinking of the a lattice parameter caused by fluorine substitution is observed and the substitutional rate of fluorine changes at x = 0.16.

Effective Ex-situ Fabrication of F-Doped SmFeAsO Wire for High Transport Critical Current Density

We demonstrate the fabrication of superconducting SmFeAsO1-xFx (Sm-1111) wires by using the ex-situ powder-in-tube technique. Sm-1111 powder and a binder composed of SmF3, samarium arsenide, and iron arsenide were used to synthesize the superconducting core. Although the F content of Sm-1111 is reduced in the process of ex-situ fabrication, the binder compensates by sufficiently supplementing the F content, thereby preventing a decrease in the superconducting transition temperature and a shrinkage of the superconducting volume fraction. Thus, in the superconducting Sm-1111 wire with the binder, the transport critical current density reaches the highest value of ~4 kA/cm2 at 4.2 K.

High-Tc Phase of PrO0.5F0.5BiS2 single crystal induced by uniaxial pressure

We demonstrated a pressure-induced phase transition from a low-Tc phase (3.5 K) to a high-Tc phase (8.7 K) in single crystalline PrO0.5F0.5BiS2. The high-Tc phase is easily observed even at 0.7 GPa by uniaxial pressure obtained from a geometric effect of a single crystal with an extremely-thin thickness. For this phase transition, superconducting anisotropy and the coherence length along the c axis change from {\gamma} = 20 to 9.3 and from {\xi}c = 0.56 to 0.71 nm respectively. It is suggested that a shrinkage in the c lattice constant by applied uniaxial pressure enhances the three dimensionality in the superconducting state.

Synthesis and physical properties of Ca1−xRExFeAs2 with RE = La–Gd

The synthesis of a series of layered iron arsenides Ca1?xRExFeAs2(112) was attempted by heating at 1000 ?C under a high pressure of 2 GPa. The 112 phase successfully forms with rare earth (RE) = La, Ce, Nd, Sm, Eu, and Gd, while RE-free samples do not contain the 112 phase. While a Ce-doped sample does not show superconductivity, La-, Pr-, Nd-, Sm-, Eu-, and Gd-doped samples show superconducting transition temperatures of 24.5, 13.2, 11.9, 11.6, 9.3, and 12.6 K, respectively, in magnetization measurements. Their Tc and Fe?Fe interlayer distances decreased with decreasing ionic radii of RE, but there are exceptions.

Site selectivity on chalcogen atoms in superconducting La(O,F)BiSSe

Single crystals of La(O,F)BiSSe were successfully grown by a CsCl flux method. Single crystal X-ray structural analysis revealed that the crystal structure is isostructural with BiS

Enhancement of the oxygen evolution reaction in Mn3+-based electrocatalysts: correlation between Jahn–Teller distortion and catalytic activity

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Pressure-dependent magnetization and magnetoresistivity studies on tetragonal FeS (mackinawite): revealing its intrinsic metallic character

- or BiSe

Pressure-induced phase transition for single-crystalline LaO0.5F0.5BiSe2

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Origin of the Higher-Tc Phase in the KxFe2−ySe2 System

-based compounds with space group