Journal of the American Ceramic Society最新文献

MAX phase ceramics, as a family of ternary layered ceramics, have received a lot of attention in the past decade due to their potential as precursors for two-dimensional transition metal carbides. However, due to complex multi-component metallurgical reactions, multicomponent MAX phase ceramics have always faced difficulties in purification and homogenization. This paper identifies a new strategy for synthesizing multicomponent MAX phase ceramics that can eliminate these synthesis difficulties. This path utilizes low-temperature (below 1000°C) stable Ti₂AlC and carbide powder as initial materials to simplify complex multi-component reactions into a one-step reaction, successfully achieving high purity and precise doping ratio. As an example, four novel doped MAX phase ceramics, Ti₂MAlC₂ (M = Nb, Ta, W) and Ti₂HEAlC₂ (HE = 1/7Ti, 1/7V, 1/7Zr, 1/7Nb, 1/7Hf, 1/7Ta, 1/7 W) were successfully synthesized using this method. This dynamic-based design, on one hand, simplifies the reaction mechanism to make purification easier, and on the other hand, the concentrated release of entropy during the reaction process promotes phase transition and related element homogenization.

Silver-based aluminosilicate photochromic glasses were prepared from 20 wt% spodumene smelting slag, by using 3 wt% AgCl (PG-Cl), 3 wt%AgNO₃ (PG-NO), and 1.5 wt%AgCl+1.5 wt%AgNO₃ (PG-Cl-NO) as the photosensitizers, respectively. The effects of the three silver-based photosensitizers on the photochromic behavior and microstructural evolution of the prepared aluminosilicate glass were systematically investigated using optical, structural, and chemical analyses. The results show that under the 365 nm UV light irradiation, PG-NO glass exhibits the strongest photochromism, with transmittance decreasing from an initial value of 78.27% to 11.17% and full self-bleaching in 180 min, while the PG-Cl glass shows the lowest transmittance decrease (remaining at 30.12%) and the fastest recovery (30 min). Moreover, the coloration depth and bleaching time significantly correlate with the density and particle size of Ag⁰ nanoparticles. AgNO₃ leads to a high concentration of photoreducible Ag⁺ in the glasses, thereby promoting Ag⁰ generation and thus the strong and durable photochromism of the PG-NO glass under UV light irradiation. These findings provide both theoretical insight and technical support for the preparation of silver-based aluminosilicate photochromic glasses with promising applications in smart windows and energy-efficient buildings.

Understanding the deformation behaviors of glass ceramics in the gradient stress field is crucial to improve their high precision processing in IC manufacturing industry. In this study, the quasistatic and time-dependent mechanical responses of lithium aluminosilicate glass ceramics containing crystalline grains were evaluated by the instrumented indentation technique at two levels of loads: 3 mN and 2 N. Anomalous behaviors like enhanced creep rate and elastic softening were observed in coarse-grained glass ceramics at 3 mN. They were rationalized as results of the spatial coupling effect between sampling volume and size of crystalline grains, as debonding and cracking may occur along the crystalline/glass interfaces in the coarse-grained glass ceramics during shallow indentations. Relevant findings can improve the processing of the fine surface of glass ceramics in the advanced industry.

Current and future high-temperature materials rely on oxide layers formed during service or applied as coatings to protect components from oxidation- and corrosion-induced damage. Understanding of defect diffusion within these oxides is often lacking, despite the central role of these processes in dictating material performance. This study investigates the intrinsic defect diffusion mechanisms in five oxides within the technologically relevant Y–Al–O system (Al₂O₃, Y₃Al₅O₁₂, YAlO₃, Y₄Al₂O₉, and Y₂O₃). Using density functional theory calculations, defect formation energies are analyzed under varying oxygen conditions to identify the most dominant defects in these oxides. Based on the formation energies under oxygen-rich conditions, our investigations into the diffusivity of energetically favorable defects reveal that Al₂O₃ exhibits the lowest defect diffusivity. In contrast, Y₂O₃ has the highest defect diffusivity due to its extensive channel structure. Additionally, we observe a trend of increasing diffusivity with higher Y₂O₃ content in the Y–Al–O series. In particular, results suggest that alloying Al₂O₃ with Y₂O₃ should ideally maintain a ratio of more than 5:3 to prevent significant increases in diffusivity and commensurate susceptibility to diffusion-controlled oxidation and corrosion damage. Ultimately, this research enhances our understanding of intrinsic defect diffusion mechanisms in complex oxides aimed at designing next-generation materials resistant to degradation in extreme environments.

In this work, Ti₃SiC₂ (TSC) MAX phase precursors were synthesized using a sol–gel method, presenting an innovative alternative to address the challenges of conventional element-based high-temperature powder synthesis, including phase purity limitations and decomposition problems. The 3:1 Ti/Si-alkoxide ratio provided the best results for starting materials with different stoichiometries (1:1, 3:2, 2:1, and 3:1). Fourier transform infrared (FTIR), thermogravimetric (TG), and X-ray diffraction (XRD) analyses confirmed the partial hydrolysis and condensation of the precursors, as well as the formation of Ti–O–Si bonds with organic groups. TSC raw materials were subjected to heat treatment at 1150–1350°C for 30–60 min. The most successful formation of Ti₃SiC₂ was achieved at 1350°C for 60 min, and MnO₂ was employed in a separate crucible as an oxygen scavenger to suppress oxide formation. According to Raman, scanning electron microscopy (SEM), transmission electron microscope (TEM), and XRD analyses, a layered Ti₃SiC₂ with a micron size was synthesized. The purity of the synthesized Ti₃SiC₂ was determined to be above 96 wt%. Furthermore, powders consolidated by spark plasma sintering (SPS) at 1300°C under 40 MPa for 5 min achieved a relative density of 97%, demonstrating good sinterability. These findings highlight the sol–gel method as a promising approach for producing high-purity MAX phase precursors.

As a pivotal optical material, the microstructure of YAG (yttrium aluminum garnet) nanocrystalline ceramics directly determines their laser and luminescent performance. This study demonstrates that rare-earth doping at grain boundaries significantly improves sintering behavior through a dual-stage regulation mechanism: during the initial stage (relative density 65%–90%), dopants (Nd/Ce) suppress mass diffusion by stabilizing grain boundary structures; whereas in the intermediate stage (75-85% relative density), they enhance diffusion by modifying grain boundary energy states. This kinetic regulation enables Nd-doped samples to achieve 99.3% relative density at 1200°C (50°C lower than pure YAG) while maintaining grain size at 57–64 nm. The doped systems achieved the requisite thermodynamic state for successful two-step sintering at significantly lower T₁ temperatures (Nd-YAG: 1175°C, Ce-YAG: 1175°C) compared with pure YAG (1200°C). The study confirms that Nd/Ce doping achieves coordinated densification-grain growth control through grain boundary segregation, providing critical theoretical guidance for fabricating high-performance transparent ceramics, particularly for developing novel Nd/Ce:YAG laser and scintillation ceramics.

The structure of the amber chromophore, a Fe³⁺ oxysulfide complex, is investigated in a suite of soda-lime glasses, using optical absorption spectroscopy (UV-Vis-NIR), Raman spectroscopy, and electron paramagnetic resonance (EPR). These spectroscopic data on glasses containing a similar Fe-content show an outstanding linear variation as a function of S concentration. This chemical dependence allows us to assign a composite Raman band at 420 cm⁻¹ to the presence of Fe-S bonds. EPR data indicate that the classical EPR signal of Fe³⁺ in glasses coexists with another signal showing an axial distortion of the Fe³⁺ site, due to O²⁻-S²⁻ substitution. These data support the presence of tetrahedral Fe³⁺ in a mixed ligand configuration with three O and one S neighbors. The two optical absorption bands observed in the UV range, near 24,200 and 34,000 cm⁻¹, are due to S²⁻—Fe³⁺ and O²⁻—Fe³⁺ charge transfer transitions within the chromophore, respectively. The former is at the origin of a broad Gaussian-shaped absorption band, causing a tail that extends into the visible range. The absence of a discrete absorption band in the visible range, together with a continuously increasing absorption with increasing wavenumbers, causes the original brown color of amber glasses. The amber chromophore concerns only a minority of Fe³⁺ sites, as shown by EPR. However, as the electronic transitions associated with charge transfer are allowed and intense, the amber chromophore has an efficient coloring power. The Fe²⁺ optical absorption spectrum remains identical to that observed in soda-lime glasses containing iron, without specific site distortion, showing the absence of substituted sulfide ligands in the coordination site of Fe²⁺. The control of the melting atmosphere conditions for chromophore formation plays a crucial role. Glass melting experiments in platinum or graphite crucibles are consistent with the literature, indicating that glasses develop an amber color only under intermediate redox conditions, estimated to correspond to an oxygen partial pressure in the range of 10⁻¹⁰ to 10⁻⁸ atm. Above and below this range, S²⁻ and Fe³⁺ do not coexist, and the glass is colorless.

Moiré superlattice architecture by stacking two-dimensional (2D) monolayers with a relative angle of twist keeps delivering emerging functionalities. Since the discovery of this novel lattice architecture, this concept has rapidly progressed in 2D van der Waals materials. Synthesis of freestanding single-crystalline oxide membranes made it possible to extend this concept to predominantly ionic nano membranes. Our work demonstrates the observation of natural moiré superlattice formation in as-synthesized bulk Ca₂MnO₄ (n = 1) Ruddlesden–Popper (RP) member. Our investigation confirms the coexistence of tetragonal I4₁/acd, orthorhombic Acam structural phases, and the 90° orientational variant of the orthorhombic phase along the [001] axis with a well-defined orientation relationship. These coexisting variants are present in nano lamellae type morphology stacked along the [001] axis. Relative in-plane rotation among these stacked nano lamellae by a fixed angle of approximately 2.9° leads to the formation of a moiré superlattice with chessboard-type nanodomains contrast, each nanodomain is approximately 3.66 × 3.66 nm in size, sharing {220} type interfaces. The modulation wavelength of the moiré superlattice along the <110> type direction is approximately 7.32 nm. A decrease in bandgap value of Ca₂MnO₄ by approximately 0.16 eV is observed.

Nanoporous anatase TiO₂, widely used in catalysis and sensing due to its high specific area, is usually exposed to mechanical solicitations in service. Several studies have examined how nanoscale porosity affects elastic modulus and hardness; however, the deformation mechanisms, as well as the role of porosity and pore radius in mechanical properties, remain unclear. In this work, the mechanical response of nanoporous anatase is studied through nanoindentation and molecular dynamics simulations using reactive interactions. Virtual samples with varying porosities and pore radii are uniaxially loaded along two high-symmetry directions. Results show that the elastic modulus for both experiments and simulations decreases linearly with porosity. In addition, plastic yield stress decreases with increasing porosity, consistent with nanoindentation experiments. Elastic deformation is followed by shear localization and directional amorphization as the preferred plasticity mechanism. Regarding the pore structure collapse, it was highly anisotropic due to localized directional amorphization. Moreover, the evolution of porosity during compression is well described by a sigmoidal model. This deformation without dislocation activity is consistent with previous studies on materials with covalent and partially ionic bonds. The proposed mechanism helps prevent brittle fracture and enables property tailoring for technological applications.

Currently, transition metal oxides (TMOs) are increasingly recognized as viable anode materials for lithium-ion batteries (LIBs). Among them, V₂O₅ has become a research focus in view of its high theoretical specific capacity, but its relatively low electrical conductivity and practical cycling capacity limit its application. It is shown that the amorphous V₂O₅-P₂O₅ negative electrode material, due to its glassy structure, on the one hand, inhibits the volume strain and particle pulverization of graphite and vanadium components during charging and discharging processes and reduces the volume expansion phenomenon in battery cycling, and, on the other hand, the formation of ion-conducting interfacial layer (PO₄³ with Li⁺ -network) to promote lithium ion transport, which has a broad application prospect. Based on this, a series of (X) graphite-(100-X) vanadium-pentoxide glass composite anode materials were prepared by mechanical ball milling method in this paper. The addition of graphite provides a stable layered structure and conductive network, realizes the reversible embedding/de-embedding of lithium ions, improves the electrical conductivity of the composite materials, and reduces the charge transfer resistance of vanadium-phosphorus glass anode materials in the cycling process. The performance of the five groups of composite anode materials showed an increasing and then decreasing trend, with the best performance observed in the 40% graphite-60% vanadium-based glass composites sample. Even after undergoing 500 cycles at 500 mA·g⁻¹, the material maintained high discharge and charge capacities of 509.3 and 510.2 mAh·g⁻¹, respectively, and the electrode sheet's surface remained relatively flat after cycling, with no obvious swelling, showing excellent cycling stability.