Hosono Hideo

Cobalt-Substitution-Induced Superconductivity in a New Compound with ZrCuSiAs-Type Structure, SrFeAsF

We have synthesized a quaternary fluoroarsenide SrFeAsF with the ZrCuSiAs-type structure (P4/nmm, a = 0.3999 and c = 0.8973 nm), which is composed of an alternately stacked (FeAs)- and (SrF)+ layers, analogous to the FeAs-based superconductor LaFeAsO. SrFeAsF shows metallic type conduction with the anomaly at ~180 K. The partial replacement of the Fe with Co suppresses the anomaly and induces the superconductivity, while the maximal Tc (4 K for SrFe0.875Co0.125AsF) is much lower than that of the Co-substituted LaFeAsO. Replacement of (LaO)+ layers with (SrF)+ layers results in a enlargement of the c-axis length (+2.6%). These results suggest the importance of interlayer interaction as a critical Tc-controlling factor in FeAs-based superconductors.We have synthesized a quaternary fluoroarsenide SrFeAsF with the ZrCuSiAs-type structure ( P 4/ n m m , a = 0.3999 and c = 0.8973 nm), which is composed of an alternately stacked (FeAs) δ- and (SrF) δ+ layers, analogous to the FeAs-based superconductor LaFeAsO. SrFeAsF shows metallic type conduction with the anomaly at ∼180 K. The partial replacement of the Fe with Co suppresses the anomaly and induces the superconductivity, while the maximal T c (4 K for SrFe 0.875 Co 0.125 AsF) is much lower than that of the Co-substituted LaFeAsO. Replacement of (LaO) δ+ layers with (SrF) δ+ layers results in a enlargement of the c -axis length (+2.6%). These results suggest the importance of interlayer interaction as a critical T c -controlling factor in FeAs-based superconductors.

Layered Iron Pnictide Superconductors: Discovery and Current Status

On February 23, 2008, our paper reporting T c of 26 K in LaFeAsO 1- x F x was published on line in the Journal of American Chemical Society. The present article describes our research flow to this discovery and summarizes research advances on Fe (Ni)-based superconductors since then. Emphases are placed on that (1) all the superconducting materials reported to date have square lattice of Fe ions whose 3d orbitals predominately contribute the Fermi level. (2) Occurrence of crystallographic transition from tetragonal phase to a lower symmetry phase is required for parent phases of high T c . (3) There are a variety of materials with different chemical compositions as candidates for high T c superconductors. Even Fe ions may be substituted by Co ion without drastically reducing T c . Fabrication of epitaxial thin films of Co-substituted Sr(FeAs) 2 exhibiting T c =20 K is also described.

Depth profiles of deuterium and phosphorus colloid formation in BaO · P2O5 glasses by D+ ion irradiation

Abstract BaO · P2O5 glasses were irradiated with D+ ions of 50 and 100 keV at room temperature to doses of 10 17 –10 18 cm 2 . Optical absorption above 2 eV was observed for high dose irradiation and this is ascribed to P colloids. The deuterium density was analyzed using the D(3He, 4He)p nuclear reaction. Appreciable diffusion towards the surface and release of D from the probing depth (∼ 4 μm) at room temperature was observed. Several percent of implanted Ds remaining after annealing at 220°C are considered to be stable, possibly occurring in the form of D-O bonds. These results indicate replacement of P-O by D-O bonds by D+ ion irradiation. An extreme non-Gaussian distribution or permeation of a non-negligible fraction of deuterium was observed for a thinner (0.15 mm) sample.

Photoemission Study of the Electronic Structure of LaFeAsO1-xFx and LaFePO1-xFx

We have performed a photoemission spectroscopy study of the newly discovered iron-based superconductors LaFeAsO 1- x F x and LaFePO 1- x F x . The valence-band spectra show a narrow Fe 3 d -derived band near E F indicating the itinerant character of the Fe 3 d states. In going from the undoped to F-doped compounds, all the spectra are found to shift to higher binding energies, consistent with electron doping within the rigid-band model. Also, in going from LaFeAsO 1- x F x to LaFePO 1- x F x , the near- E F intensity increases reflecting the weakening of electron correlation.

Plasticity of Fe-Oxypnictides Superconductor

Compressive deformation of LaFeAsO 0.9 F 0.1 was examined in a He gas at temperatures 1373–1673 K. Extraordinary large deformation (up to true strain of 1.6, the height of the specimen reduced to 1/5 of the original height) was observed at strain rate 10 -4 s -1 and at 1673 K. XRD revealed the preferential orientation along crystallographic c -axis occured during deformation. The superconducting phase ( T c - 26 K) could be retained after the deformation.