Journal of the American Ceramic Society最新文献

Open-cell ceramic foams with controllable cell connectivity were fabricated by polymethyl methacrylate (PMMA) microspheres as pore-forming agent combined with particle-stabilized foaming method. In order to adjust the open-cell structures of ceramic foams, PMMA microspheres with distinct particle sizes and contents were used. The results indicate that the bubble-derived pores in the prepared ceramic foams were interconnected by microsphere-derived pores within cell walls, and the average size and volume fraction of microsphere-derived pores and bubble-derived pores could be tailored by adjusting the particle size and content of PMMA microspheres. The impacts of open-cell structures on connectivity were described in terms of permeability in this study. The open-cell ceramic foams obtained using larger PMMA particle size and content exhibited larger Darcian and non-Darcian permeability constants due to the increase of the size and volume fraction of microsphere-derived pores. The ratio of Darcian and non-Darcian permeability constant represents the individual contribution of viscous and inertial effects to the total pressure drop during the permeation process that are strongly dependent on the microsphere-derived pore size and pore volume fraction. The Darcian and non-Darcian constants in this study were in the range of 3.54 × 10⁻¹² to 4.09 × 10⁻¹¹ m² and 3.05 × 10⁻⁷ to 5.10 × 10⁻⁶ m, respectively. These results are of practical value for the preparation and optimization of ceramic foams in applications requiring open-cell structures.

Wide band gap metal oxides can increase the detection band and performance of photodetectors. Among them, zinc oxide (ZnO) is a multi-functional oxide metal with various applications in various areas, that is, gas sensors, electronics, and optoelectronics. In this study, we employed ZnO metal oxide layers, which were synthesized by hydrothermal method, as interfacial layers for Schottky-type silicon-based photodetectors between Au metal and p-Si with 46 and 56 mM ZnO solution molarities to fabricate Au/ZnO/p-Si heterostructures. Synthesized ZnO morphology and crystallinity were tested by scanning electron microscopy and x-ray diffraction techniques. The Au/ZnO/p-Si heterostructures were investigated for photodetector applications by current–voltage (I–V) analysis in various light densities ranging from dark to 150 mW/cm², and different wavelengths for the same light irradiance power. I–V characteristics under dark and light situations were used to extract diode characteristics and light detection parameters. The impedance analysis technique was also employed to demonstrate the capacitance behavior for the Au/ZnO/p-Si heterostructures. The obtained Au/ZnO/p-Si heterostructures confirms that trap levels are important to obtain high-performance photodetectors.

This study investigates the mechanisms behind fluidity loss in superplasticized limestone calcined clay cement (LC3), a sustainable alternative to ordinary Portland cement (OPC). Despite its environmental benefits, in presence of superplasticizers, LC3 experiences significant challenges in maintaining workability, an issue of which this paper examines the root cause. It focuses on the role that initial reactions play in creating additional surface area and the consequence thereof on the performance of polycarboxylate ether superplasticizers (PCE) in LC3. Experimental results reveal that while PCEs initially disperse the cement particles, fluidity decreases rapidly over time, primarily due to the continuous generation of those new surfaces that exceed the adsorption capacity of PCEs. The study also examines the potential intercalation of PCE side chains into calcined clays and shows that even in the worst-case scenario with montmorillonite clays, intercalation is not a significant contributor to slump loss when the clays are calcined. These findings suggest that alternative strategies, such as slowing down the initial reactivity of the calcined clays, for example by combining PCEs with other additives like diphosphonates, may be necessary to improve flow retention in superplasticized LC3 systems.

This study employs a data-driven machine learning approach to investigate specific ferroelectric properties of Al_1−xSc_xN thin films, targeting their application in next-generation nonvolatile memory (NVM) devices. This approach analyzes a vast design space, encompassing over a million data points, to predict a wide range of coercive field values that are crucial for optimizing Al_1−xSc_xN-based NVM devices. We evaluated seven machine learning models to predict the coercive field across a range of conditions, identifying the random forest algorithm as the most accurate, with a test R² value of 0.88. The model utilized five key features: film thickness, measurement frequency, operating temperature, scandium concentration, and growth temperature to predict the design space. Our analysis spans 13 distinct scandium concentrations and 13 growth temperatures, encompassing thicknesses from 9–1000 nm, frequencies from 1 to 100 kHz, and operating temperatures from 273 to 700 K. The predictions revealed dominant coercive field values between 3.0 and 4.5 MV/cm, offering valuable insights for the precise engineering of Al_1−xSc_xN-based NVM devices. This work underscores the potential of machine learning in guiding the development of advanced ferroelectric materials with tailored properties for enhanced device performance.

Graphene nanoplatelets (GNPs) offer excellent support for a diverse array of composite applications. Herein, Co_0.5Mg_0.5Fe_1.8La_0.2O₄ (CMFL) and its composites were prepared by the sol–gel autocombustion method. X-ray diffraction confirmed the formation of a single-phase structure, with both the average crystallite size (34.33–46.30 nm) and the lattice constant (8.292–8.411 Å) increasing with GNP insertion. The presence of graphene in the nanocomposites was confirmed by Raman spectroscopy, which revealed a D band at 1376.38 cm⁻¹. The Fourier transform infrared spectra indicated the existence of absorption bands corresponding to tetrahedral (534.46–525.94 cm⁻¹) and octahedral (456.62–454.95 cm⁻¹) structures. The optical bandgap energy (E_g) varied when the compositions of the samples were changed, with the lowest value of E_g being 2.58 eV for CMFL/2.5 wt.% GNPs. The DC electrical resistivity increased from 6.73 × 10⁴ to 1.07 × 10⁶ Ω cm, indicating that the composite materials might be appropriate for use in transformers and telecommunications devices. With increasing frequency, the dielectric constant and loss decreased, whereas the AC conductivity improved. The Cole–Cole behavior showed that the conduction mechanism had non-Debye relaxation characteristics. The saturation magnetization increased from 25.86 to 42.75 emu/g for the synthesized samples, and the coercivity demonstrated a variable trend.

We report on the fabrication and optical properties of erbium-doped Y₂O₃–MgO and Gd₂O₃–MgO nanocomposite ceramics, with a particular focus on their mid-infrared emission. The ceramics were fabricated by a self-propagating high-temperature synthesis followed by hot pressing. The transmittance of 1.7 mm-thick 5 at.% Er:Y₂O₃–MgO and 7 at.% Er:Gd₂O₃–MgO ceramics at 3 µm amounted to 79.4% and 21.5%, respectively. This difference in transmission, as revealed by microstructural analysis, is due to variation in the distribution of residual pore sizes, while the average grain size is almost the same for both ceramics, being ∼200 nm. The composites exhibited luminescence in the visible, near-infrared, and mid-infrared spectral ranges attributed to electronic transitions of Er³⁺ ions in the cubic sesquioxide phase. Peculiarities in the Raman and luminescence spectra were identified in comparison to single-phase Er:Y₂O₃ and Er:Gd₂O₃ ceramics, which may indicate certain solubility of MgO in the sesquioxide phase of the composites.

Glass substrate for organic light-emitting diodes (OLED) requires to undergo several heating processes and thus makes a thermal shrinkage of glass substrate. The shrinkage leads to a pixel shifting and becomes a key factor affecting OLED panel quality. To understand the thermal shrinkage process, it is crucial to study the structural relaxation and thermodynamic characteristics of glass substrate around the glass transition temperature. In this work, the network structure of alkali-free aluminosilicate glasses and their structural relaxation in the glass transition temperature range were studied by both experiment and molecular dynamics (MD) simulations. The alkali-free aluminosilicate glasses with 15.3–22.1 mol% alkali-earth oxides (RO) were prepared, and their reheating shrinkage and enthalpy relaxation were measured to reflect the structural relaxation during thermal cycling. As the RO content increased from 15.3 to 22.1 mol%, the CTE_25–300°C increased from 3.00 × 10⁻⁶ to 4.13 × 10⁻⁶/°C, and the strain point decreased from 780 to 744°C. The reheating shrinkage of 4 × 4 × 40 mm glass rods also increased from 4.01 to 9.51 ppm, and the volume shrinkage primarily occurred in the initial stages of holding at 600°C. The enthalpy relaxation of the glass was measured using differential scanning calorimetry, and there were very small enthalpy relaxation in alkali-free aluminosilicate glasses due to their good thermal stability. Therefore, MD simulations were employed to calculate the potential energy and evaluate the structural relaxation. The potential energy of the glasses during thermal cycling revealed a significant energy hysteresis upon reheating, and the structural relaxation occurred at relatively low temperature with the increasing addition of RO contents. Further analysis confirmed that the structural relaxation of glasses was mainly due to the structural arrangement of alkali-earth metal ions, including the changes in bond length, angles, coordination number, and atomic mean-square distance.

Steel slag, a major industrial waste in China, possesses significant CO₂ absorption potential. In this study, the CO₂ sequestration of steel slag reached up to 15.6%; however, excessive mineralization resulted in reduced hydration activity. Compared to unmineralized slag, the 1-day compressive strength decreased by 15.9%, and cumulative hydration heat over 72 h dropped by 8%. Using advanced visualization techniques such as scanning electron microscopy-backscattered electron (SEM-BSE), 3D X-ray, and focused ion beam-transmission electron microscopy (FIB-TEM), the study reveals the microstructure of overmineralized steel slag, identifying a composition of a calcite outer layer, an amorphous SiO₂ layer, a transition area, and an unmineralized core. The mineralization reaction affected 84.80% of the steel slag particles, with volume expansion causing dense regions to become porous, increasing porosity from 0% to 1.62%. This expansion also risks lattice distortion. During CO₂ mineralization, a dense calcite layer forms, blocking the hydration of internal silicate gels and calcium silicate minerals, reducing the hydration activity of overmineralized slag. This study offers insights for optimizing CO₂ mineralization techniques and applications for steel slag.

The series of successful inertial confinement fusion ignitions from December 2022 to December 2023 marked a groundbreaking milestone in humanity's pursuit for a new, inexhaustible source of clean energy. At the core of this ignition system lies the potassium dihydrogen phosphate (KDP) crystals, playing an indispensable role. However, ensuring the reliable, long-term application of KDP components relies heavily on their quality, necessitating finishes that are free from damage or nearly so. Manufacturing KDP components poses significant challenges due to their fragility, unstable microstructure, sensitivity to environmental factors and complex mechanical behavior. To address the quest for damage-free manufacturing, interdisciplinary investigations have been commenced, incorporating theoretical analyses, atomistic simulations, and experimental trials. The success of the ignitions has catalyzed intensified research efforts aimed at achieving damage-free machining of KDP components, drawing significant attention. This review is dedicated to examining existing studies on machining-induced damage mechanisms and exploring potential pathways for achieving damage-free machining of KDP crystals.

(Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ persistent luminescence (PersL) ceramics were fabricated by solid-state reactive pre-sintering in vacuum combined with hot isostatic pressing (HIP) post-treatment adding H₃BO₃ as a sintering additive. The influence of pre-sintering temperature on the phase composition, microstructure, and PersL performance of (Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ ceramics was investigated. The results showed that optimum persistent performance was obtained by the ceramics prepared by vacuum pre-sintered at 1600°C for 3 h and HIP post-treated at 1400°C for 3 h under 200 MPa in Ar. The persistent initial luminescence intensity exceeded 9200 mcd/m² after 5 min when the optimum sample was simulated by the daylight irradiation of 1000 lx, and the persistent emission decay time was longer than 14 h. The trap depth was calculated using two methods, and the results showed that the ceramics prepared at pre-sintering temperature of 1600°C had the highest trap depth.