A fundamental issue concerning iron-based superconductivity is the roles of electronic nematicity and magnetism in realising high transition temperature (T c). To address this issue, FeSe is a key material, as it exhibits a unique pressure phase diagram involving non-magnetic nematic and pressure-induced antiferromagnetic ordered phases. However, as these two phases in FeSe have considerable overlap, how each order affects superconductivity remains perplexing. Here we construct the three-dimensional electronic phase diagram, temperature (T) against pressure (P) and isovalent S-substitution (x), for FeSe1−xSx. By simultaneously tuning chemical and physical pressures, against which the chalcogen height shows a contrasting variation, we achieve a complete separation of nematic and antiferromagnetic phases. In between, an extended non-magnetic tetragonal phase emerges, where T c shows a striking enhancement. The completed phase diagram uncovers that high-T c superconductivity lies near both ends of the dome-shaped antiferromagnetic phase, whereas T c remains low near the nematic critical point.

The three-dimensional (3D) distribution and oxidation state of a Pt cathode catalyst in a practical membrane electrode assembly (MEA) were visualized in a practical polymer electrolyte fuel cell (PEFC) under fuel-cell operating conditions. Operando 3D computed-tomography imaging with X-ray absorption near edge structure (XANES) spectroscopy (CT-XANES) clearly revealed the heterogeneous migration and degradation of Pt cathode catalyst in an MEA during accelerated degradation test (ADT) of PEFC. The degradative Pt migration proceeded over the entire cathode catalyst layer and spread to MEA depth direction into the Nafion membrane.

Mixed-anion perovskites such as oxynitrides, oxyfluorides, and oxyhydrides have flexibility in their anion arrangements, which potentially enables functional material design based on coordination chemistry. However, difficulty in the control of the anion arrangement has prevented the realization of this concept. In this study, we demonstrate strain engineering of the anion arrangement in epitaxial thin films of the CaSrTaON perovskite oxynitrides. Under compressive epitaxial strain, the axial sites in TaON octahedra tend to be occupied by nitrogen rather than oxygen, which was revealed by N and O K-edge linearly polarized X-ray absorption near-edge structure (LP-XANES) and scanning transmission electron microscopy combined with electron energy loss spectroscopy. Furthermore, detailed analysis of the LP-XANES indicated that the high occupancy of nitrogen at the axial sites is due to the partial formation of a metastable trans-type anion configuration. These results are expected to serve as a guide for the material design of mixed-anion compounds based on their anion arrangements.

The CoFeB/MgO system shows promise as a magnetic tunnel junction with perpendicular magnetization and low critical current densities for spin-torque driven magnetization switching. The distribution of B after annealing is believed to be critical to performance. We have studied the distribution of B in a Ta/Co0.2Fe0.6B0.2/MgO sample annealed at 300 °C for 1 h with standing-wave hard x-ray photoemission spectroscopy (SW-HXPS). Comparing experimental rocking curve data to x-ray optical calculations indicates diffusion of 19.5% of the B uniformly into the MgO and of 23.5% into a thin TaB interface layer. SW-HXPS is effective for probing depth distributions in such spintronic structures.

The crystal structure of the excitonic insulator Ta 2 NiSe 5 has been investigated under a range of pressures, as determined by the complementary analysis of both single-crystal and powder synchrotron X-ray diffraction measurements. The monoclinic ambient-pressure excitonic insulator phase II transforms upon warming or under a modest pressure to give the semiconducting C-centred orthorhombic phase I. At higher pressures (i.e. >3 GPa), transformation to the primitive orthorhombic semimetal phase III occurs. This transformation from phase I to phase III is a pressure-induced first-order phase transition, which takes place through coherent sliding between weakly coupled layers. This structural phase transition is significantly influenced by Coulombic interactions in the geometric arrangement between interlayer Se ions. Furthermore, upon cooling, phase III transforms into the monoclinic phase IV, which is analogous to the excitonic insulator phase II. Finally, the excitonic interactions appear to be retained despite the observed layer sliding transition.

Catalyst degradation at the cathode of a membrane electrode assembly (MEA) remains a critical issue for practical polymer electrolyte fuel cell (PEFC) operation, but such wet systems impede detailed visualization of degradation events in the cell during its operation. In this work, for the first time, operando spectroimaging (X-ray absorption near-edge structure−computed tomography) was used to produce clear three-dimensional (3D) images of the morphology, Pt and Co distributions, Co/Pt atomic ratio, and Pt valence state of a Pt−Co/C cathode catalyst in a PEFC MEA before and after performing a PEFC-accelerated degradation test. The infographic approach combining the operando spectroimaging and unsupervised learning of the 3D images revealed a catalyst degradation mechanism with different degradation behaviors for Pt and Co in the bimetallic catalyst and negligible migration of the Pt catalyst in local parts of the MEA.

For gate insulator of amorphous InGaZnO thin-film transistor, we fabricated fluorinated silicon nitride (SiN:F) film formed by an inductively-coupled plasma enhanced chemical vapor deposition method by utilizing SiF4/N2 as source gases. Threshold voltage shift against electrical stress was successfully suppressed. Chemical analysis revealed that the hydrogen concentration was reduced to 1/10 of conventional SiN film and fluorine was introduced into the interface between the SiN:F film and channel layer. We conclude that the decrease of hydrogen content and introduction of fluorine lead to decrease of electron trap density at the interface and/or the SiN:F film.

1T-TiSe 2 has a semimetallic band structure at room temperature and undergoes phase transition to a triple-q charge density wave (CDW) state with a commensurate superlattice structure (2a × 2a × 2c) below T c ≈ 200 K at ambient pressure. This phase transition is caused by cooperative phenomena involving electron-phonon and electron-hole (excitonic) interactions, and cannot be described by a standard CDW framework. By Cu intercalation or the application of pressure, this phase transition temperature is suppressed and superconductivity (SC) appears. However, it is not clear what kind of order parameters are affected by these two procedures. We investigated the crystal structure of Cu x TiSe 2 and pressurized 1T-TiSe 2 around the SC state by synchrotron x-ray diffraction on single crystals. In the high-temperature phase, the variation of structural parameters for the case of Cu intercalation and application of pressure are considerably different. Moreover, the relationship between the critical points of the CDW phase transition and the SC dome are also different for the two cases. The excitonic interaction appears to play an important role in the P−T phase diagram of 1T-TiSe 2 , but not in the x−T phase diagram.