Journal of the American Ceramic Society最新文献

Nickel titanate (NiTiO₃) nanostructured materials have gained extensive attention in the field of lithium-ion batteries (LIBs) due to their high theoretical capacity and low cost. However, NiTiO₃ exhibits low conductivity and significant volume changes during cycling, resulting in capacity decay and poor cycling stability. Herein, we propose a feasible strategy to enhance the cycling performance of NiTiO₃ nanostructures by adjusting their morphology. By manipulating the choice of solvent employed in the synthetic process, we obtain NiTiO₃ microbars (NTO MBs) through self-assembly of NiTiO₃ nanoparticles (NTO NPs). When utilized as an anode material in LIBs, NTO MBs exhibit a capacity of 410 mAh g⁻¹ after 200 cycles at 100 mA g⁻¹, surpassing that of NTO NPs (212 mAh g⁻¹). The improved performance of NTO MBs is attributed to their unique porous bar-like structure, composed of numerous NPs, which provides a substantial storage space for Li⁺ ions owing to its larger specific surface area. Additionally, the porous structure accelerates the diffusion of Li⁺ ions and electron transfer. To gain a profound understanding of the enhanced performance through morphology adjustment, we conduct a comprehensive investigation on the growth mechanism of NTO MBs. This work provides valuable insights into the mechanism governing the morphology control of NTO MBs, facilitating the rational design and synthesis of tailored materials with enhanced performance for LIBs.

Using fly ash (FA) to modify magnesium phosphate cement (MPC) not only extends setting time and enhances MPC performance but also reduces costs. Currently, high-quality FA is predominantly used, whereas the accumulation of low-quality FA poses challenges for waste management and environmental protection. This study focuses on low-quality FA with excessive sulfur content. Initially, X-ray fluorescence spectroscopy was employed to select two types of FA with SO₃ contents of 1.06% and 6.07%. FA replaced magnesium oxide in equal mass to prepare FA/MPC composite cementitious materials. The composite materials were studied for hydration heat, phase composition, infrared spectroscopy, mechanical properties, and microscopic morphology to explore SO₃’s impact on MPC hydration processes, microstructure, and properties. The findings indicate that adding FA effectively dilutes reactants, extending setting time from 7 to 17 min and 18 min, aiding construction operations. In the FA/MPC composite cementitious materials, MPC hydration, along with FA's synergistic hydration, forms a new hydration product MgSiO₃, improving material density and mechanical strength post-hardening. Excessive SO₃ in high-sulfur FA accelerates MgO decomposition, providing ample Mg²⁺ for K-struvite synthesis, promoting MPC hydration, and transforming K-struvite from amorphous to crystalline, enhancing material strength.

Oxide ceramic matrix composites (Ox-CMCs) are composed of porous matrices reinforced by dense fibers to achieve high damage tolerance. It is generally assumed that their mechanical properties are fiber dominant. However, fiber strength can also be influenced by the surrounding matrix as it can affect fiber grain growth. Fiber–matrix interactions are studied in this work regarding fiber microstructural evolution and composite strength. Minicomposites containing Nextel 610 fibers and different matrix compositions (alumina, alumina–zirconia, and mullite–alumina) are evaluated after sintering and after additional heat treatment at 1200°C for 100 h. Fiber grain growth during sintering is faster in alumina matrix and slower in mullite–alumina matrix. Scanning transmission electron microscope–energy-dispersive X-ray spectroscopy (STEM–EDX) measurements show that Si diffuses between fiber and matrix grain boundaries. This outward or inward diffusion of SiO₂ leads to the respectively different grain growth kinetics. Grain growth inhibition in alumina–zirconia matrix is only observed after the longer heat treatment, suggesting that ZrO₂ diffusion is slower than SiO₂. The resultant composite strength depends not only on fiber properties, but also on matrix densification. Minicomposite with alumina–zirconia matrix showed higher strength, while mullite–alumina composites showed higher thermal stability. In summary, the properties of Ox-CMCs can be tailored by adjusting the matrix composition with the used fibers.

Fluorescence intensity ratio (FIR) thermometry has been regarded as new optical thermometry because of its faster response, higher sensitivity, and accuracy. However, improving the sensitivity is still a challenge. Here, Ba₂LuNbO₆:Er³⁺,Yb³⁺ up-conversion specimens were synthesized, characterized, and designed for dual-mode thermometry based on FIR. The ²H_11/2/⁴S_3/2 thermally coupled energy levels (TCELs) and ²H_11/2/⁴F_9/2 non-TCELs (NTCELs) of Er³⁺ were selected as two FIR modes for optical thermometry. The energy gap of ²H_11/2/⁴S_3/2 TCELs of Er³⁺ in Ba₂LuNbO₆:Er³⁺,Yb³⁺ phosphors was confirmed as 977 cm⁻¹. Therefore, the maximal relative sensitivity (S_r) of FIR based on TCELs is 1.53% K⁻¹ @ 303 K. For FIR based on NTCELs, a higher maximal S_r value of 1.81% K⁻¹ @ 303 K is obtained, which surpasses other Er³⁺-doped up-conversion specimens. In addition, the phosphors exhibit excellent thermal fatigue resistance and temperature resolution. Results suggest that Ba₂LuNbO₆:Er³⁺,Yb³⁺ specimens might be applied in the temperature sensing field.

Phosphate glasses have garnered significant attention as host materials for various laser applications due to their high rare-earth ion solubility, large stimulated emission cross-section, and low nonlinear refractive index. Modification of phosphate glass composition is feasible through poly-anion substitution, leading to poly-anionic glasses with unique properties. This study explores the glass-forming regions (GFRs) of AlF₃-R₂SO₄-M(PO₃)₂-based poly-anionic fluoro-sulfo-phosphate (R/M-FSP) glasses, a promising class of ionic glasses. Theoretical GFRs are predicted using a thermodynamic approach and then validated through a few experiments. The experimental GFRs range from K/Ba-FSP > Na/Ba-FSP > Li/Ba-FSP > K/Sr-FSP > Na/Sr-FSP > Li/Sr-FSP, with wider areas observed under lower cation field strength. Notably, the K/Ba-FSP glass system exhibits high anti-crystallization stability (approximately 140°C) and a low nonlinear refractive index (1.43 × 10^–13–1.83 × 10^–13 esu), advantageous for high-power laser operations. Furthermore, a comparative study among K/Ba-FSP glasses elucidates the general principles of manipulating glass structure and physical properties through compositional variation.

Transparent glass-ceramics (GCs) are promising for applications that require both optical clarity and superior mechanical strength, such as high-performance displays and ballistic armor. However, achieving this combination typically involves a trade-off, as crystallization processes that enhance mechanical properties often compromise transparency. This study investigates the optimization of mechanical properties in transparent and translucent MgO-Al₂O₃-SiO₂ (MAS) GCs. We examine the heat treatment conditions necessary for achieving various levels of transparency and evaluate the influence of crystal size and volume fraction on Vickers hardness, indentation crack resistance, and fracture toughness (K_Ic). Our findings indicate that, depending on the composition and heat treatment conditions, even nanocrystals smaller than 100 nm can diminish transparency, rendering the GCs translucent. Translucent and opaque samples exhibit superior mechanical performance due to higher crystallized fractions and larger crystals. However, specific thermal protocols were identified to produce transparent GCs (visible light transmittance > 80% for 1.5 mm thick samples) with at least a 30% increase in K_Ic compared to their parent glasses. This study demonstrates the feasibility of balancing transparency and mechanical strength in MAS GCs through careful optimization of processing parameters.

The magneto-optical properties of rare-earth-rich borate glasses prepared using a levitation technique were thoroughly investigated. Among the series of rare-earth borate glasses, Tb₂O₃–B₂O₃ and Dy₂O₃–B₂O₃ glasses displayed remarkably large Faraday effects in the visible region. The Verdet constant of 58Tb₂O₃–42B₂O₃ reached −229 rad/T·m at 633 nm, surpassing the value of commercially available single-crystalline Tb₃Ga₅O₁₂. Compositions with a higher rare-earth oxide content (60 mol%) than that of binary glasses facilitated the successful synthesis of Tb₂O₃–Dy₂O₃–B₂O₃ ternary glasses. The Verdet constant linearly increased with increasing Tb₂O₃ content for the glasses with 40 mol% B₂O₃. Results indicate that rare-earth-rich borate glasses are promising candidates for magneto-optical applications in the visible region, and that the types and amounts of rare-earth ion mainly affect these properties.

Green and sustainable energy alternatives to replace fossil fuels are a topic of research in scientific community, thus yielding pursuit of advancing renewable energy systems with hydrogen emerging as a suitable and viable alternative. Efficient and non-precious metal catalysts are crucial for large-scale electrochemical water splitting yielding clean H₂. Here, a novel two-step hydrothermal synthesis approach to fabricate manganese–cobalt selenide nano-cubes grown directly on nickel foam (NF) (MnCo₂Se₄/NF) is adopted. Leveraging its hierarchically structured architecture, augmented active sites, and electrochemically active surface area, MnCo₂Se₄/NF material demonstrates exceptional electrocatalytic performance for both water oxidation and reduction. With an overpotential of 233 mV for oxygen evolution reaction (OER) and 187 mV for hydrogen evolution reaction at a current density of 10 mA/cm², MnCo₂Se₄/NF also exhibits a Tafel slope of 44 mV/dec for sluggish OER process. Notably, this nanocrystalline catalyst displays enhanced catalytic activity under alkaline conditions, accelerates water dissociation, and maintains good stability over 50 h. Outperforming state-of-the-art RuO₂, particularly in two-electrode assemblies with an overpotential of 218 mV at 10 mA/cm², this work offers a promising pathway for designing and manufacturing of innovative bifunctional electrocatalysts for efficient water splitting processes, thereby contributing to broader goal of sustainable energy production.

This study investigates the dynamics of ice crystal growth and stress distribution in nanoconfined spaces using molecular dynamics simulations. First, the interaction between the pore wall and coarse-grained water is modified, leading to the development of pore models with varying wettability. Subsequently, the process of ice crystal growth within pores of 10 nm diameter is examined under different temperatures and hydrophobicity conditions. Results unveil that ice crystal growth induces substantial energy and enthalpy alterations within the system. Hydrophobic nanopores demonstrate a protective function by limiting ice crystal growth and water transport, thereby mitigating freezing damage. However, hydrophobic nanopores exhibit increased stress levels when saturated with water. The study employs the Zener pinning theory and mass transfer rates to qualitatively scrutinize the thermodynamic and kinetic interplay between the ice crystal interface and the degree of supercooling. These findings offer insights into the mechanisms of ice formation and stress evolution in nanoconfined environments.