Journal of the American Ceramic Society最新文献

The development of high-efficiency, non-precious metal electrocatalysts for the hydrogen evolution reactions (HERs) that operate robustly in both acidic and alkaline electrolytes is essential to replace costly Pt-based catalysts. In this study, we present a novel heterostructure design: Mo‒Mo₂C nanoparticles embedded within nitrogen and carbon co-doped nanofibers (denoted as Mo‒Mo₂C/NC NFs), fabricated via an organic‒inorganic hybridization strategy and subsequent hydrogen reduction. Our key material innovation lies in the precise regulation of the metallic Mo content, and thus the density of Mo‒Mo₂C heterostructures, by controlling the aniline monomer dosage during synthesis. Comprehensive experimental characterization confirms that strong electronic coupling at these heterointerfaces effectively modulates the local electron density, leading to optimize hydrogen adsorption energy and enhanced H₂ desorption kinetics. Furthermore, the ternary conductive network, comprising metallic Mo, Mo₂C nanoparticles, and N, C-doped carbon, synergistically promotes charge transfer and inhibits nanoparticle agglomeration. As a result, the optimized electrocatalyst exhibits notable HER performance, achieving competitive overpotentials of 167 mV in 0.5 M H₂SO₄ and 140 mV in 1 M KOH at 10 mA cm^‒2, with Tafel slopes of 81 and 86 mV dec^‒1, respectively. This work differentiates from prior Mo₂C-based systems by deliberate multi-component interface engineering and presents a general strategy for designing high-performance, pH-universal electrocatalysts through precise heterostructure control.

Structural fluctuations exist within glass-forming systems because of their non-crystalline structure and interactions between network formers and modifiers. A comprehensive understanding of structural fluctuations could be used to predict nucleation and crystallization in glass-forming systems. In this work, we investigate structural fluctuations from a computational perspective to provide atomic-scale insights into their fundamental mechanisms. A series of binary barium silicate glasses across a range of compositions were chosen for this study. Molecular dynamic simulations were used to analyze the fluctuations for bonding interactions, bond-angle distributions, and Qⁿ distributions. Topological constraint theory is applied for predicting the rigidity of glass network form analyzing the bonds constraints and angular constraints within the glass matrix. Our approach combines molecular dynamic simulations with topological constraint theory to reveal the local rigidity and structural fluctuations within glass-forming systems at different temperatures.

Special service environments challenge the metallic interconnector (MIC) of solid oxide fuel cells with high-temperature oxidation, interfacial reactions, and persistent Cr⁶⁺ volatilization. Notably, high p(H₂O) in the anode environment would further accelerate the Cr volatilization and confront the MIC with non-negligible oxidation issues. We systematically investigated three CeO₂-coated MIC (AMIC 21/SUS 443/Crofer 22H)//anode systems during long-term operation under 700°C@90% H₂–10% H₂O conditions. Key findings reveal that both the sputtering pressure and deposition temperature significantly enhance CeO₂ grain size and crystallinity. Among the three systems, CeO₂/Crofer 22H demonstrates superior oxidation resistance, characterized by minimal oxide growth (52.6 nm kh⁻¹). However, CeO₂/SUS 443 achieved the lowest ASR increase rate of 13.4% kh⁻¹, outperforming CeO₂/AMIC21 (48.8% kh⁻¹) or CeO₂/Crofer 22H (46.7% kh⁻¹). After assembling with Ni-GDC anode, final interface resistances of 32.6, 31.1, and 27.4 mΩ cm⁻² were achieved for Ni-GDC//CeO₂/AMIC21, Ni-GDC//CeO₂/SUS 443, and Ni-GDC//CeO₂/Crofer 22H. This work demonstrates that CeO₂ coating exhibits not only excellent compatibility and interfacial stability with the Ni-based anode but also maintains stable conductivity and provides effective protection under MIC/anode service conditions.

Luminescence thermometry with near-infrared (NIR) emission proves their performance in deeper tissue penetration in biological tissues due to significantly reduced absorption and scattering compared to visible wavelengths. Herein, Er³⁺,Tm³⁺ co-doped TiO₂ nanofibers with anti-thermal quenching behavior have been developed for temperature sensing applications in the first and second biological windows. The temperature dependent luminescence intensity ratio (FIR) of Tm³⁺: ³H₄ → ³H₆ and Er³⁺: ⁴I_11/2→ ⁴I_15/2 electronic transitions demonstrate exceptional sensitivity (Sr = 3.59% K⁻¹ at 298 K) and temperature resolution less than 1 K within 298–398 k temperature range. Validation using intralipid tissue phantom reveals a penetration depth of 17.35 mm, underscoring the material's potential for in vitro applications.

Soft magnetic composites (SMCs) are magnetic materials composed of ferromagnetic cores with insulating coatings that minimize eddy current losses, making them attractive for high-frequency electronic applications. This work reports a new strategy for fabricating SMCs based on Fe@Fe₃O₄ core–shell particles combined with a polyvinylidene fluoride (PVDF) binder using low-temperature cold sintering, without high-temperature annealing. The Fe₃O₄ shell provides electrical insulation while maintaining the high magnetization of Fe, and the addition of PVDF enhances compaction and further increases resistivity. Structural characterization confirmed the successful formation of the Fe@Fe₃O₄ phase. The results show that small PVDF additions improve density and hardness, whereas excessive PVDF causes phase separation and reduces mechanical strength. From a magnetic and electrical standpoint, PVDF incorporation decreases saturation magnetization (196 emu/g at 0% to 157 emu/g at 20%) but greatly suppresses eddy current loss, down to 12 mW/cm³ at 100 kHz, with resistivity rising to ∼8500 mΩ cm. The optimal balance occurs at 7.5% PVDF, giving M_s = 181 emu/g and total loss of 235.1 mW/cm³ at 100 kHz. These results highlight Fe@Fe₃O₄/PVDF composites as promising candidates for high-frequency magnetic applications requiring low core loss.

The viscosity, fragility index, and shear relaxation dynamics of a range of sodium borosilicate (NBS) liquids have been studied using a combination of differential scanning calorimetry, beam-bending viscometry, and shear-mechanical spectroscopy (SMS). Our results show a non-monotonic compositional variation of the isokom temperature T₁₂ corresponding to a viscosity of 10¹² Pa s and the fragility index m, consistent with the known structural evolution involving boron coordination change and non-bridging oxygen formation. A negative correlation is observed between T₁₂ and m. On the other hand, the quantity (T_g − T₁₂), where T_g is the glass transition temperature, becomes increasingly positive as m decreases below ∼50, which suggests an increase in the temporal decoupling between enthalpy and shear relaxation with decreasing fragility in these NBS liquids. SMS measurements, which involve frequency- and temperature-dependent scans of storage and loss moduli, are shown to yield shear relaxation timescales that are consistent with those derived from viscosity via the Maxwell model. Furthermore, the dynamical heterogeneity associated with the shear relaxation of these liquids as estimated from the Kohlrausch–Williams–Watts stretching exponent β, remains temperature-independent near T_g in fragile NBS liquids but increases with temperature for the strongest liquid. This observation supports recent findings of distinct β(T) behavior in strong versus fragile liquids. Similarly, consistent with the recent results for organic liquids, no correlation is observed between m and β near T_g for NBS liquids.

Oxygen defect tuning engineering is an effective method to tailor the properties of ceramic materials. However, persistent difficulties remain in the controllable generation of intrinsic oxygen vacancy defects ($�V_o^{�n�+�}$) in the AlON lattice, and their influence on transparency remains elusive. Here, by regulating the CRN synthesis temperature to implant thermal-induced $�V_o^{�n�+�}$ intrinsic defects into AlON powder, we report that higher temperature would cause the lattice oxygen to be lost from the AlON crystal, and result in the AlON powder exhibiting a distinct gray color. Besides, through an analysis of the sintering kinetics in ceramics fabrication, AlON ceramics prepared from powder with more $�V_o^{�n�+�}$ defects show a high transmittance up to 82%, while the counterpart ceramic only achieves a transmittance of 76%. The study of intrinsic $�V_o^{�n�+�}$ defects on ceramics transparency in this work provides a reference approach for fabricating AlON transparent ceramic.

Some materials are difficult to sinter by flash method, as they require both extremely high temperatures and intense electric fields. For such materials, a common strategy is to mix them with a powder of an easily flashable material that acts as a catalyst. Here we demonstrate that HfO₂, which is difficult to flash even at very high fields and very high furnace temperatures, can be sintered by flash in a bilayer configuration with yttria-stabilized zirconia. Flash in zirconia layer propagated into the hafnia layer, made from monoclinic powders, causing it to flash and sinter at 800°C. The HfO₂ layer sintered to a relative density of ∼95%, with a grain size of 470 nm. Dielectric constant of the flash-sintered HfO₂ was comparable to conventionally sintered and FAST/spark plasma-sintered–processed specimens. The present method offers a viable route to overcome the long-standing challenge of densifying high-resistance refractory ceramics without the use of sintering aids.

Cracks are a phenomenon found in various natural situations, yet they represent a long-standing challenge as a critical defect in industrial fields. For instance, cracks formed during the drying of colloidal slurries lead to performance degradation and disruptions in processing. Although numerous experimental and theoretical approaches have been explored to understand and control crack formation, its complex mechanisms remain difficult to comprehend systematically. Here, we demonstrate a novel perspective that cracking can be understood through the thixotropic behavior of slurries. The elastic structural recovery that determines thixotropy is quantitatively evaluated using aqueous colloidal slurries with alumina particles as a model. Furthermore, this elastic force is shown to be highly sensitive to changes in particle dispersion. A key finding is the strong correlation between the elastic structural recovery of slurry and crack formation during drying. Based on the multifaceted experimental results, we elucidate the hidden physics of thixotropy as a crucial indicator of durability against drying-induced stresses.

Semiconducting BaTiO₃-based ceramics for positive temperature coefficient (PTC) thermistors have conventionally been sintered at ∼1400°C in a reducing atmosphere. In the present study, sintered BaTiO₃-based semiconductor ceramics were obtained by exposing green compacts of BaTiO₃ powder to Na vapor in an Ar atmosphere. The Na vapor functioned as both a reducing agent and a sintering accelerator. Densification and grain growth of BaTiO₃ proceeded during heating at 800°C or higher. PTC thermistor properties with 1.9 orders of magnitude were observed at temperatures near the Curie temperature of BaTiO₃ (120°C). Contamination of sodium in the BaTiO₃-based ceramics was rather small (∼ 0.2 wt%) and tiny areas containing Na were found in some of the fracture surfaces of ceramics.