Science China Materials最新文献

Oxidation resistance is critical for high-entropy diborides (HEBs) to be used as thermal structural components under oxygen-containing high-temperature environments. Here, we successfully realize the exploitation of (Zr, Ta, Cr, W) B₂ HEBs with superior oxidation resistance by comprehensively screening their compositions. To be specific, 21 kinds of HEB-xTM (x = 0–25 mol%, TM = Zr, Ta, Cr, and W) samples are fabricated via an ultrafast high-temperature sintering technique. The as-fabricated HEB-5Cr samples show the best oxidation resistance at 1673 K among all the samples. Subsquent oxidation investigations further confirm the as-fabricated HEB-5Cr samples possess superior oxidation resistance with the parabolic oxidation behavior across 1473–1773 K. Such superior oxidation resistance is believed to result from the multi-component synergistic effects. Particularly, the Ta⁵⁺ and W⁴⁺ cations with high ionic field strengths can promote the formation of ⁴B–O–⁴B linkages between [BO₄] tetrahedrons by charge balance, which can stabilize the three-dimensional skeletal structure of B₂O₃ glass and consequently result in an improved viscosity of the B₂O₃ glassy layer. In addition, the ZrO₂ and Cr₂O₃ with high melting points can dissolve into the B₂O₃ glass to increase its glass transition temperature, leading to an enhanced viscosity of the B₂O₃ glassy layer.

Two-dimensional (2D) antiferromagnetic (AFM) skyrmions are free from stray magnetic field and skyrmion Hall effect, and can be driven by a small current density up to a high speed, desirable for low-power spintronic applications. However, most 2D AFM skyrmions are realized in complex heterostructured materials, which impedes the dense integration of spintronic devices. Here, we propose that 2D AFM skyrmions can be achieved in ruthenium tetrafluoride (RuF₄) monolayer using hybrid functional theory combined with atomistic spin dynamics simulations. Our study indicates that 2D RuF₄ is dynamically stable and its nondegenerate vibration modes in optical branches are either Raman or infrared active. Furthermore, 2D RuF₄ acts as an indirect bandgap semiconductor with an out-of-plane AFM state. Notably, the presence of a weak Dzyaloshinskii-Moriya interaction in 2D RuF₄ leads to a spin spiral ground state at low temperatures, enabling the formation of AFM skyrmions with possible length modulation by an external magnetic field. Our results give insight into 2D RuF₄ and may provide an intriguing platform for 2D AFM skyrmion-based spintronic applications.

Advancing our understanding of global climate, particularly in polar regions, requires accurate detection of carbon dioxide (CO₂) in ice cores and deep sea environments. However, detecting trace levels of CO₂ in these areas presents significant challenges. We introduce a novel preconcentration approach using functionalized zeolitic imidazolate framework, ZIF-8(CN), for the detection of ultra-low CO₂. ZIF-8(CN) has small pores (4.4 Å) and cyano groups (–CN), enabling highly selective adsorption of CO₂ (36.2 cm³ g⁻¹) over N₂ (1.6 cm³ g⁻¹) at 298 K. The mechanism involves unique –CN⋯CO₂⋯–CN interactions within the pore structure. When cast into a film on an aluminum substrate, ZIF-8(CN) demonstrates exceptional CO₂ preconcentration capability (1 ppm in N₂) with an extraordinary preconcentration factor of 748, outperforming traditional ZIF and zeolite materials. Additionally, a ZIF-8(CN) preconcentrator is designed and fabricated with bionic gas flow of fractal structure which optimizes the gas-film contact, and thus its performance is further improved by 115%.

Hybrid ferroelastic crystals have garnered considerable interest due to their promising potential as mechanical switches and sensors. The anomalous ferroelastic phase transitions, in which ferroelasticity occurs in the high-temperature phase rather than the low-temperature phase, are of particular interest, but they are sporadically-documented and none of them is involved in breaking of the chemical bonds. Herein, a hydroxyl-containing cation, i.e., Me₃NOH⁺, is employed to construct a three-dimensional hybrid crystal (Me₃NOH)₂KBiCl₆ (1). This crystal undergoes distinct two-step structural phase transitions with space-group changes of Pna2₁–P112₁–P6₃mc, belonging to an anomalous temperature-reversed mm2F2 ferroelastic transition and a normal 6mmF2 ferroelastic transition, respectively. The anomalous ferroelastic transition is entirely driven by switchable K–O coordination bonds involving breaking and reformation. Notably, the dynamic behavior of Me₃NOH⁺ cations along with the distortion of inorganic framework enables the manifestation of unusual “high-low-medium” second-harmonic generation-switching behaviors. This study presents the enormous benefits of switchable coordination bonds for inducing anomalous ferroelastic phase transitions, offering valuable insight for the exploration of new multifunctional ferroelastic materials.

Phase change materials (PCMs) have attracted significant attention in thermal management due to their ability to store and release large amounts of heat during phase transitions. However, their widespread application is restricted by leakage issues. Encapsulating PCMs within polymeric microcapsules is a promising strategy to prevent leakage and increase heat transfer area with matrices. Moreover, photothermal PCM microcapsules are particularly desirable for solar energy storage. Herein, we fabricated photothermal PCM microcapsules with melamine-formaldehyde resin (MF) as shell using cellulose nanocrystal (CNC) and graphene oxide (GO) co-stabilized Pickering emulsion droplets as templates. CNC displays outstanding Pickering emulsifying ability and can facilitate the fixation of GO at the oil-water interface, resulting in a stable CNC/GO co-stabilized PCM Pickering emulsion. A polydopamine (PDA) layer was coated in-situ on the emulsion droplets via oxidization self-polymerization of dopamine. Meanwhile, GO was reduced to reduced GO (rGO) due to the reducing ability of PDA. The outmost MF shell of the PCM microcapsules was formed in-situ through the polymerization and crosslinking of MF prepolymer. The resulted PCM@CNC/rGO/PDA/MF microcapsules exhibit uniform sizes in the micrometer range, excellent leakage-proof performance, high phase change enthalpy (175.4 J g⁻¹) and PCM encapsulation content (84.2%). Moreover, the presence of rGO and PDA endows PCM@CNC/rGO/PDA/MF microcapsules with outstanding photothermal conversion performance. The temperature of PCM@CNC/rGO/PDA/MF microcapsule slurries (15wt.%) can reach 73°C after light irradiation at 1 W cm⁻². Therefore, photothermal PCM@CNC/rGO/PDA/MF microcapsules are promising for solar energy harvesting, thermal energy storage, and release in various applications, such as energy-efficient buildings and smart textiles.

Maintaining low modulus while endowing the wide-range linear stretchability to wearable or implantable devices is crucial for these devices to reduce the mechanical mismatch between the devices and human skin/tissue interfaces. However, improving linear stretchability often results in an increased modulus of stretchable electronic materials, which hinders their conformability in long-term quantifiable monitoring of organs. Herein, we develop a hybrid structure involving interlocking low-modulus porous elastomers (Ecoflex-0030) and MXene-based hydrogels with crosslinking networks of polyvinyl alcohol, sodium alginate, and MXene. This hydrogel–elastomer structure exhibits superior performance compared with previous reports, with a wide linear stretchability strain range from 0 to 1000% and maintaining a low modulus of 6.4 kPa. Moreover, the hydrogel–elastomer hybrids can be utilized as highly sensitive strain sensors with remarkable characteristics, including high sensitivity (gauge factor ∼3.52), a linear correlation between the resistance and strain (0–200%), rapid response (0.18 s) and recovery times (0.21 s), and excellent electrical reproducibility (1000 loading–unloading cycles). Those electrical and mechanical properties allow the sensor to act as a suitable quantifiable equipment in organ monitoring, human activities detecting, and human–machine interactions.