Science and Technology of Advanced Materials最新文献

We demonstrate high-throughput evaluation of the half-metallicity of Co₂MnSi Heusler alloys by spin-integrated hard X-ray photoelectron spectroscopy (HAXPES) of composition-spread films performed with high-brilliance synchrotron radiation at NanoTerasu, which identifies the optimum composition showing the best half-metallicity. Co_75-x Mn _x Si₂₅ composition-spread thin films for x = 10-40% with a thickness of 30 nm are fabricated on MgO(100) substrates using combinatorial sputtering technique. The L2₁-ordering and (001)-oriented epitaxial growth of Co₂MnSi are confirmed by X-ray diffraction for x = 18-40%. The valence band HAXPES spectra exhibit a systematic compositional dependence and the smallest photoemission intensity at the Fermi level (E _F) for a slightly Mn-rich composition of x = 27%. The density of states (DOS) for L2₁-ordered Co₂MnSi with different Mn compositions obtained from first-principles calculation also show the smallest total DOS at E _F for x = 27% because of the formation of a clear half-metallic gap in the minority spin channel and the less localized d-states in the majority spin channel, indicating the best half-metallic nature of this composition. Our experimental results demonstrate that high-throughput evaluation of half-metallicity is possible even with spin-integrated HAXPES by capturing systematic changes in the electronic structures through the measurements on the composition-spread film. Moreover, the anisotropic magnetoresistance (AMR) of the composition-spread film is measured for electric current directions along the [110] and [100] of Co₂MnSi. Previous studies indicated that a larger negative AMR ratio is a signature of a higher spin polarization. The largest negative AMR ratio is observed for x = 27% for both current directions, which also supports the best half-metallicity for this off-stoichiometric composition.

Alkaline-earth metal oxides with the rocksalt structure, which are simple ionic solids, have attracted attention in attempts to gain fundamental insights into the properties of metal oxides. The surfaces of alkaline-earth metal oxides are considered promising catalysts for the oxidative coupling of methane (OCM); however, the development of such catalysts remains a central research topic. In this paper, we performed first-principles calculations to investigate the ability of four alkaline-earth metal oxides (MgO, CaO, SrO, and BaO) to catalyze the OCM. We adopted five types of surfaces of rocksalt phases as research targets: the (100), (110), stepped (100), oxygen-terminated octopolar (111), and metal-terminated octopolar (111) surfaces. We found that the formation energy of surface O vacancies is a good descriptor for the adsorption energy of a H atom and a methyl radical. The energies related to the OCM mechanism show that, compared with the most stable surface, the minor surfaces better promote the C - H bond cleavage of methane. However, as the trade-off for this advantage, the minor surfaces exhibit increased affinity for the methyl radical. On the basis of this trade-off relationship between properties, we identified several surfaces that we expect to be promising OCM catalysts. Our investigation of the temperature dependence of the Gibbs free energy indicated that, at higher temperatures, the step (100) surface exhibits properties that might benefit the OCM mechanism.

Hydrogen-assisted (HA) fatigue crack growth (FCG) occurs in ferritic steels, wherein H-dislocation interaction plays a vital role. We aim to model the HAFCG mechanism based on the obstruction of dislocations within the crack tip zone. Our modeling framework is as follows: H is condensed into crack tip and trapped by dislocations; these H significantly decrease dislocation mobility; stress relief via crack blunting is suppressed; localized brittle fracture triggers HAFCG. This model was substantiated experimentally in H₂ gas at various load frequencies and temperatures. Theoretical formulations were established considering the thermal equilibrium of H-trapping and dislocation breakaway from the H atmosphere.

In this review, we present a new set of machine learning-based materials research methodologies for polycrystalline materials developed through the Core Research for Evolutionary Science and Technology project of the Japan Science and Technology Agency. We focus on the constituents of polycrystalline materials (i.e. grains, grain boundaries [GBs], and microstructures) and summarize their various aspects (experimental synthesis, artificial single GBs, multiscale experimental data acquisition via electron microscopy, formation process modeling, property description modeling, 3D reconstruction, and data-driven design methods). Specifically, we discuss a mechanochemical process involving high-energy milling, in situ observation of microstructural formation using 3D scanning transmission electron microscopy, phase-field modeling coupled with Bayesian data assimilation, nano-orientation analysis via scanning precession electron diffraction, semantic segmentation using neural network models, and the Bayesian-optimization-based process design using BOXVIA software. As a proof of concept, a researcher- and data-driven process design methodology is applied to a polycrystalline iron-based superconductor to evaluate its bulk magnet properties. Finally, future challenges and prospects for data-driven material development and iron-based superconductors are discussed.

Poly(_L-lysine)-block-poly(ethylene glycol)-block-poly(_L-lysine) (PLys-block-PEG-block-PLys) triblock copolymers formed polyion complex (PIC) with poly(acrylic acid) (PAAc) or sodium poly(styrenesulfonate) (PSS), leading to the formation of flower micelle-type nanoparticles (Nano^Lys/PAAc or Nano^Lys/PSS) with tens of nanometers size in water at a polymer concentration of 10 mg/mL. The flower micelles exhibited irreversible temperature-driven sol-gel transitions at physiological ionic strength, even at low polymer concentrations such as 40 mg/mL, making them promising candidates for injectable hydrogel applications. Rheological studies showed that the chain length of PLys segments and the choice of polyanions significantly impacted irreversible hydrogel formation, with PSS being superior to PAAc for the formation. The incorporation of silica gel nanoparticles into the PIC flower micelles also resulted in irreversible gelation phenomena. The highest storage modulus exceeded 10 kPa after gelation, which is sufficient for practical applications. This study demonstrates the potential of these PIC-based hydrogels as biomaterials with tunable properties for biomedical applications.

The paper presents a study on the fabrication of a lightweight acoustic hyperbolic paraboloid (HyPar) diaphragm using self-assembly nanoarchitectonics. The diaphragm is composed of a polyacrylonitrile (PAN) network combined with graphene oxide (GO) nanolayers. Spray coating is employed as a fabrication method, providing a simple and cost-effective approach to create large-scale curved diaphragms. The results demonstrate that the PAN/GO diaphragm exhibits acoustic performance comparable to a commercially available banana pulp diaphragm while significantly reducing weight and thickness. Notably, the graphene-based diaphragm is 15 times thinner and 8 times lighter than the commercial banana pulp diaphragm. This thinner and lighter nature of the graphene-based diaphragm offers advantages in applications where weight and size constraints are critical, such as in portable audio devices or acoustic sensors.