High-critical-temperature (T c ) superconductivity at 48 K is reported for hydrogen-doped SmFeAsO epitaxial films on MgO single-crystal substrates. The key processes are pulsed laser deposition to grow undoped SmFeAsO epitaxial films and subsequent topotactic chemical reaction using CaH 2 powders under evacuated silica-glass ampule atmosphere. Based on this post-deposition thermal annealing treatment that we have developed, a maximum hydrogen concentration x = ~0.35 was realized in SmFeAs(O 1x H x ). Disordered hydrogen-substitution at O sites is experimentally confirmed directly by atomic-scale microstructural observations. Magnetization measurement validates the bulk nature of the high-T c superconductivity in the films. This method will become an effective and general method to fabricate various high-quality oxyhydride epitaxial films.

Size-dependent reaction of nickel-doped silver cluster cations (Ag N¹1 Ni + : N = 514) was investigated for oxygen as the reactant molecule. A dramatic drop in the reactivity observed for N ² 9 is attributed to the encapsulation of the nickel atom, i.e., screening the active site at larger sizes. The reactivity minimum observed at N = 10 is ascribed to the closed electronic shell of Ag 9 Ni + formed by 18 valence electrons from Ag5s, Ni4s, and Ni3d, suggesting delocalized d electrons.Keywords: Nickel-doped silver cluster | Size-dependent reactivity | s-d hybridizationClusters are known to exhibit physical and chemical properties dependent on the size, i.e., the number of constituent atoms. One of the key factors determining their properties is the electronic structure. For example, electronic structures of alkali-and coinage-metal clusters are known to be described by electronic shells in the quantum-well scheme, which are occupied by valence s electrons (itinerant electrons) of the constituent atoms.1,2 This electronic-shell structure is modified when other orbitals such as p and d contribute to the shell. One attempt to modify the electronic structure is doping a transitionmetal atom, i.e., adding d electrons to the cluster. However, it is not trivial to illustrate an electronic structure of such a doped system because it is not obvious whether the d orbitals of the dopant atom would hybridize with the s orbitals of the host cluster to contribute to the itinerant electrons. Several experimental and theoretical studies have been conducted to elucidate this issue. Size distributions of transition-metal-doped coinagemetal clusters produced after photofragmentation were examined by mass spectrometry.36 Electronic structures were probed by anion photoelectron spectroscopy along with density functional theory (DFT) calculations. 7 More recently, X-ray magnetic circular dichroism (XMCD) spectroscopy was performed for investigating magnetic properties, i.e., spin states. 8 These studies revealed that 3d electrons tend to be delocalized like s electrons when the electronic structure of the entire cluster forms a closed shell with a contribution of the 3d electrons, 37 whereas they tend to be localized to show high-spin states when the host cluster itself forms a closed electronic shell. 8 The electronic structure is also important for the chemical reactivity of clusters. Nonose et al. reported the reactivity of vanadium-doped cobalt clusters in their earlier work.9 They found that the reactivity of Co 12 V toward H 2 adsorption is less than that of Co 13 due to the lowered electron density on the surface of the Co 12 V cluster, which was explained theoretically as well. 10 In reactions of clusters involving transition metals, unpaired 3d electrons play an important role. Therefore, the reactivity of transition-metal-doped clusters is expected to be modified by manipulating the number of unpaired d electrons (i.e., spin state) on the dopant atom. Such manipulation is materialized by size-dependent sd hybridization in a ...

Four kinds of binary hydrides (MgH2, CaH2, SrH2, and BaH2) were added to evacuated silica-glass ampules containing undoped SmFeAsO epitaxial films. Post-deposition thermal annealing was performed to dope hydrogen into the films. The annealing temperature was optimized for each hydride. Critical temperatures of >40 K and critical current densities (Jc) ≥ ∼1 MA cm−2 at 2 K and a self-field were observed in the hydrogen-doped films annealed with CaH2, SrH2, and BaH2. This result would lead to acceleration of biaxially textured coated conductor researches on hydrogen-doped SmFeAsO exhibiting high-Jc performance for high-field magnet application.

The electronic transport properties of a highly hydrogen-substituted 1111-type SmFeAsO epitaxial film with high critical-temperature (Tc = 45 K) were investigated under high magnetic fields. By using a single-turn magnet generating up to 130 T, we clarified that the upper critical field (μ0Hc2) of SmFeAsO0.65H0.35 is 120 T at the nearly low-temperature limit of 2.2 K for μ0H || ab. The angular dependence of μ0Hc2 revealed that the anisotropic parameter (γ) around Tc is ~2, which is comparable with that of a practical candidate 122-type BaFe2As2 with lower Tc and much smaller than that of Fsubstituted SmFeAsO. The small γ mainly originates from the high hydrogen incorporation. The extremely high μ0Hc2 and small γ, together with the high Tc and high critical current density, suggest that SmFeAsO1−xHx has high potential for the superconducting electromagnets and cables.