Science and Technology of Advanced Materials最新文献

Additive manufacturing (AM) of bimetallic structures combining copper alloys and Ni-based superalloys is critical for extreme environmental applications. However, interface cracking during fabrication persists due to thermophysical property mismatches. By implementing a CALPHAD-based ICME framework (CALPHAD: Calculation of Phase Diagrams; ICME: Integrated Computational Materials Engineering), we decode nonequilibrium solidification and phase stability to predict cracking susceptibility. Liquid phase separation emerges as the dominant mechanism, altering solute redistribution and thermal stress accumulation - a previously underexplored factor in bimetallic systems. Experiments using wire arc additive manufacturing (WAAM) validate model prediction: crack-free interfaces between C18150 and In625 require intermediate layers with 65 wt.% In625. This composition mitigates cracking with the lowest cracking susceptibility coefficient (CSC). Importantly, we establish a quantitative correlation between phase separation and CSC, proposing a way to analyze systems exhibiting these microstructural features. This work uses ICME methodologies by linking thermochemical modeling to process optimization, offering new principles for designing defect-resistant bimetallic components in extreme environments such as rocket engine nozzles.

Stable lithium plating/stripping of metallic lithium anode is considered as the urgent challenge for the development of post-lithium-ion batteries including lithium-sulphur and lithium-air batteries. In this work, we report a new facile and cost-effective method to grow a protective layer on the surface of lithium metal through immersing the lithium surface in a nitrogen-saturated solution that eliminates the operational restrictions of reported modification approaches in controlled atmosphere. N₂-treated lithium shows prolonged cycling in a symmetric configuration and chemical stability. We demonstrate that the treated Li anode notably enhances the cycling stability, coulombic efficiency, as well as the rate capability of lithium-sulphur cells.

This review summarizes our recent developments in capacitor-type heat flow switching devices that enable active control of heat flow magnitude through the modulation of electron thermal conductivity. We initially demonstrated the feasibility of a capacitor-type heat flow switching device using silver chalcogenides, Ag₂S_1-x Se _x , as an electrode material with very low lattice thermal conductivity (≤0.5 W m^-1 K^-1). We achieved significant enhancements in heat flow switching performance through subsequent improvements, including electrode thinning and the implementation of an electric double-layer capacitor structure with ionic liquids. The switching ratio improved from an initial value of 1.1 at the bias voltage of V _B = +3 V to 1.9 at V _B = +2.4 V, while response times were estimated to be less than 0.2 s. This review discusses the operating principles, experimental methods, and performance metrics across different device configurations, highlighting the critical role of electrode materials with extremely low lattice thermal conductivity. Our findings establish a promising candidate for practical thermal management applications that require rapid and reliable heat flow control without mechanical components.

Molecular photoswitches are incorporated into materials to impart photoresponsiveness, enabling a wide range of fascinating applications. Although their surrounding environments within materials strongly influence the photoresponsive and thermally reversible behaviors through physical and chemical interactions, these effects remain poorly understood. In this study, we investigate the two-way photoisomerization and thermal back-isomerization of spiropyran (SP)-a representative photoswitch that undergoes large polarity changes upon the reversible isomerization to merocyanine (MC)-chemically integrated into diblock copolymers (dBCPs) exhibiting either ordered or disordered microphase separation. We synthesize a series of dBCPs consisting of a high-glass-transition-temperature (T _g) poly(methyl methacrylate) block and a low-T _g statistical copolymer block of SP acrylate and n-butyl acrylate, with varying compositions, molecular weights, and microphase-separated structures. The results reveal that the rates of both the SP-to-MC and MC-to-SP photoisomerization processes differ substantially between ordered and disordered microphase-separated structures but are comparable among the different ordered morphologies. In contrast, the photoisomerization yields are scarcely affected by the microphase separation. These findings provide valuable insights into the molecular and polymer design of photoresponsive smart materials based on photoswitches and will contribute to their further development and applications.

We demonstrated rapid homoepitaxial growth on (011) β-Ga₂O₃ substrates using HCl-based halide vapor phase epitaxy (HVPE), in which GaCl was synthesized by reacting metallic Ga with HCl gas, and examined properties of the resulting layer. These were compared with layers grown using Cl₂-based HVPE, where GaCl was produced from Ga and Cl₂. The growth rate on (011) substrates, approximately 60% of that on (001), reached ~14 μm/h, which was 5-7 times higher than those previously reported for Cl₂-based HVPE. Despite this high rate, no polycrystalline grains, sometimes found in Cl₂-based HVPE, were detected. Atomic force microscopy revealed a surface with root-mean-square roughness of 6.5 nm over a 100 × 100 μm² area. In contrast, Nomarski microscopy revealed the presence of pits (~10 μm in diameter at 3.6 μm thickness) with a density of ~3.7 × 10³ cm^-2, a feature not reported for Cl₂-based HVPE. Cross-sectional transmission electron microscopy confirmed the absence of crystal defects or inclusions at the pit bottom. X-ray diffraction 2θ-ω scans and pole figure measurements confirmed that the epitaxial layers were single crystalline, with rocking-curve FWHM values comparable to or smaller than those of the substrate. Secondary ion mass spectrometry revealed a chlorine concentration of 1.7 × 10¹⁵ cm^-3, which was significantly lower than 1.1 × 10¹⁶ cm^-3 measured in the (001) layers. Thus, while the pit issue requires further investigation, HCl-based HVPE enables the rapid growth of low-chlorine (011) β-Ga₂O₃, offering significant potential for cost reduction in high-performance power devices with thick drift layers.

Iron silicide (β-FeSi₂) has attracted considerable interest as a sustainable thermoelectric material due to its abundance, non-toxicity, and environmental compatibility. Their conduction flexibility allows a wide range of dopants to tune transport behavior, creating opportunities for improved performance. However, dopant solubility limits and the formation of secondary phases remain key challenges. In this article, we highlight recent advances in strategies to enhance the thermoelectric performance of β-FeSi₂-based materials and discuss the interplay between phase evolution, electrical, and thermal transport. We also outline prospects that may unlock further improvements, offering pathways toward higher thermoelectric efficiency in this material system.

We investigate the thermal spin transport phenomena in ferromagnetic metals with an adjacent spin-polarized Pt layer examining sputter-deposited Pt/Co_1-xFe_x and Pt/Ni_1-xFe_x bilayers. We quantitatively disentangle the detected voltages generated by the spin Seebeck effect from the anomalous Nernst effect contributions arising from both the ferromagnetic metal and the spin-polarized Pt layer. Further, we probe the dependence of the aforementioned effects on the composition and on the magnetic moments of both the ferromagnetic metal and the spin-polarized Pt layer. We report a strong dependence of all effects on the composition via increase/decrease of the effect coefficients with increasing/decreasing magnetic moments of both the ferromagnetic metal and the spin-polarized Pt layer. Following our descriptions, our work provides quantitative spin Seebeck coefficients in metals and thermal spin transport coefficients in nominally non-magnetic materials such as Pt which will be the base for future designs of spin caloritronic applications.

Although simulation studies focused on polymer network rupture remain relatively limited compared to the broader field, recent advances have enabled increasingly nuanced investigations that bridge molecular structures and macroscopic failure behaviors. This review surveys the evolution of molecular simulation approaches for polymer network rupture, from early studies on related materials to state-of-the-art methods. Key challenges - including mismatched spatial and temporal scales with experiments, the validity of coarse-grained models, the choice of simulation protocols and boundary conditions, and the development of meaningful structural descriptors - are critically discussed. Special attention is paid to the assumptions underlying universality, limitations of current methodologies, and the ongoing need for theoretically sound and experimentally accessible network characterization. Continued progress in computational techniques, model development, and integration with experimental insights will be essential for a deeper, predictive understanding of polymer network rupture.

The mechanical properties of ultralight materials are influenced by their constituent materials, internal porous structures, and surface states. The surface chemical state is particularly crucial for materials composed of hydrophilic polymers such as cellulose, where interactions with ambient water are significant. In this study, we report that the reversible compressibility of ultralight carbon nanotube (CNT)/carboxymethyl cellulose (CMC) materials can be enhanced by hydrophobic surface treatment with silane coupling agents. We examined the treatment conditions for hydrophobization and investigated their impact on the microstructure and surface chemical properties of the ultralight material. The hydrophobized ultralight CNT/CMC materials with a bulk density of 1.6 mg/cm³ demonstrated superior reversible compressibility, with a 65% recovery rate even under high humidity conditions (80% RH).

The influence of relative density on the dynamic mechanical behavior of porous titanium under combined high-temperature and high-strain-rate conditions is investigated. Using validated finite element models based on three-dimensional Voronoi tessellations, simulations of Split Hopkinson Pressure Bar (SHPB) tests were conducted across a range of relative densities (0.3-0.6), strain rates (3000-8000 s^-1), and temperatures (25-550 °C). Results demonstrate that increasing relative density from 0.3 to 0.6 increases the yield stress by 511.8%, attributed to enhanced cell-wall interactions and a concomitant shift in deformation mechanisms. Strain rate strengthening and thermal softening compete, with high relative density amplifying both effects. The stress-strain curves exhibit three characteristic regimes: linear elasticity, plateau, and densification, where higher relative density shortens the plateau stage and advances densification onset. Low-density specimens (ρ _r  < 0.5) undergo layer-by-layer collapse dominated by cell-wall bending, while high-density specimens (ρ _r  > 0.5) exhibit matrix-dominated triaxial compression with reduced localized deformation. Quantitative analysis of regionally partitioned displacement confirms that strain rate intensifies the magnitude of localized deformation, whereas temperature primarily induces global softening. These insights provide a predictive framework for designing porous titanium architectures with tailored dynamic performance in extreme environments.