Journal of the American Ceramic Society最新文献

Recently, gahnite (ZnAl₂O₄) is gaining attraction as a potential refractory ceramic because of the similarity of its structure and properties with those of magnesium aluminate (MgAl₂O₄) spinel refractories. Formation of MgO and hibonite solid solution (CaMg_xAl_12−xO_19−0.5x; 0 ≤ x ≤ 0.18), CAM-I (Ca₂Mg_2−3xAl_28+2xO₄₆ (0 ≤ x ≤ 0.3), and CAM-II (CaMg_2−3xAl_16+2xO₂₇, 0 ≤ x ≤ 0.2) phases with platelet and interlocking microstructure in the CaO–Al₂O₃–MgO ternary system significantly enhances the high temperature mechanical properties of refractory castables. The CaO–Al₂O₃–ZnO ternary system has been studied, for the first time to our knowledge, in a selected compositional range with reference to the CaO–Al₂O₃–MgO system from 1650°C to 1700°C. The formation of ZnO and hibonite solid solution (CaZn_xAl_12−xO_19−0.5x; 0 < x < 0.18), CAZ-I (Ca₂Zn_2−3xAl_28+2xO₄₆; 0 ≤ x ≤ 0.3), and CAZ-II (CaZn_2−3xAl_16+2xO₂₇; 0 ≤ x ≤ 0.2) phases with platelet and interlocking morphology have been found. The crystal structures and lattice parameters of ZnO and hibonite solid solution, CAZ-I, and CAZ-II are comparable, respectively, with MgO and hibonite solid solution, CAM-I, and CAM-II. Furthermore, CAZ-I and CAZ-II phases also form due to reaction between hibonite (CaO·6Al₂O₃) and ZnAl₂O₄.

Studying the nanoindentation behavior of materials at the atomic level is crucial for advancing technologies involving energetic atom bombardment, ion implantation, and nanomechanical testing. Using molecular dynamics simulations with two typical rigid ion interatomic potentials (fixed charges), we showed that the mechanical responses and dislocation nucleation of alumina ($�\alpha$-$��{\mathrm{Al}}_2�O_3�$) are highly temperature- and orientation-dependent. The complex behavior in dislocation dynamics has been rationalized by computing the distribution of stacking fault energy. It is further found that SHIK potential provides better accuracy in describing dislocation dynamics at a much lower computational cost.

Herein, we report on the structural, magnetic, dielectric, and optical properties of La-doped Sr_2-xLa_xFe_0.5Hf_1.5O₆ (SLFHO, 0.0 ≤ x ≤ 2.0) double perovskite oxides synthesized by solid-state reaction method. X-ray powder diffraction data and their Rietveld refinement reveal that the SLFHO powders crystallize in an orthorhombic structure with the Pnma space group. The SLFHO powders exhibit spherical morphology with an average particle size of 160 nm, as shown from SEM images. Their molar ratios of the Sr:La:Fe:Hf elements were determined as 1.77:0.50:0.50:1.95 by energy dispersive X-ray spectroscopy data, approaching their nominal stoichiometry. X-ray photoelectron spectra verified that Sr²⁺, La³⁺, Fe³⁺, and Hf⁴⁺ (Hf^x+) ions existed in the SLFHO powders, and oxygen existed in species lattice oxygen and adsorbed oxygen, respectively. The SLFHO powders exhibit ferromagnetic behavior at 2 and 300 K, respectively, and at 2 K the saturated magnetization was 5.66 emu/g (or 0.60 μ_B/f.u.). Magnetic transition temperature, T_C was determined to be 867 K. Dielectric measurements demonstrated a strong frequency-dependent dielectric behavior observed in the SLFHO ceramics and a relaxor-like dielectric behavior appearing in the temperature range of 200–600 K. Such relaxor-like dielectric behavior is ascribed to the dielectric response of the singly-ionized oxygen vacancies ($��V_O^{·}��)���\mathrm{associated}��\mathrm{with}����$ an activation energy of 0.54 eV. Room temperature optical properties of the SLFHO powders examined by using UV–vis diffuse reflectance spectroscopy exhibit high optical absorption in this wavelength region, and a wide indirect optical bandgap (E_g = 3.39 eV) was estimated using the Tauc's relation from the diffuse reflectance spectra. The SLFHO double perovskite oxides display high-temperature ferrimagnetism, relaxor-like dielectric behavior, and wide optical bandgap, making them potential to be employed in the fields of high-temperature spintronics and magnetic semiconductor devices.

As a functional crystal, LiNbO₃ plays a significant role in nonlinear optics, optical storage, illumination, and three-dimensional display. Recent investigations have suggested that the precipitation of LiNbO₃ in a nonequilibrium system shows unique crystallite geometry and orientation, leading to fascinating nonlinear optical properties. This work focuses on the effect of alkaline earth metal ions on the properties of Li₂O–Nb₂O₅–SiO₂ glass ceramics. The results demonstrate that within the Li₂O–Nb₂O₅–SiO₂ glass matrix, irregularly shaped crystals of approximately 5 µm in size precipitate through volume crystallization. Upon incorporation of Mg²⁺, the glass ceramic remains in volume crystallization while LiNbO₃ crystals grow to 10 µm and become spherical. In contrast, the compositions containing Ca²⁺, Sr²⁺, and Ba²⁺ change to surface crystallization, producing submicron or even nano-sized crystals. Besides, the nonlinear optical response can be improved after the hybridization of alkaline earth metal oxides. This research offers insights into the crystallization behavior of LiNbO₃ crystals from the nonequilibrium environment.

MgO–Al₂O₃–SiO₂ (MAS) glass-ceramics are significant due to their excellent mechanical properties. However, most of these glass-ceramics are opaque and lack chemically strengthened capabilities. In this study, chemically strengthened transparent MAS glass-ceramics were successfully synthesized by employing SnO₂ + ZrO₂ + Ta₂O₅ as a multinucleating agent. Systematic investigation was conducted using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscope (TEM), field emission scanning electron microscope (FE-SEM), Scattered Light Photoelastic Stress Meter (SLP), and Vickers hardness measurements. The results show that Ta₂O₅ exhibits a good nucleation effect. With the increase of Ta₂O₅ content from 0 mol% to 0.5 mol%, the exothermic peak temperature of the precipitated crystals decreased from 976.3°C to 937.6°C. The primary crystalline phases precipitated in the MAS system were MgAl₂O₄ (PDF#21-1152) and ZnAl₂O₄ (PDF#05-0669), with secondary phases including SnO₂ (PDF#46-1088), ZrO₂ (PDF#50-1089), and Ta₂O₅ (PDF#21-1198). TEM-tested interplanar spacing data and electron diffraction ring data further confirmed the presence of these crystalline phases. At 0.5 mol% Ta₂O₅ content, after crystallization at 920°C, the average grain size was approximately 40.34 nm, with 86.57% transmittance at 550 nm. The Vickers hardness of the parent glass increased from 6.68 GPa to 7.17 GPa after heat treatment at 920°C. Following 5 h of ion exchange, Vickers hardness increased to 7.97 GPa, with surface compressive stress (CS) of 150.29 MPa and depth of layer (DOL_zero) of 80.96 µm. After 24 h of ion exchange, Vickers hardness reached 8.16 GPa, with CS of 239.86 MPa and DOL_zero of 93.28 µm. The conclusions provide new insights for further study of the MAS system and broaden its application field such as in cover materials.

Optical thermometric and anti-counterfeiting multifunctional materials hold great promise for practical applications, yet their development continues to encounter considerable challenges. Here, we successfully developed a new Bi³⁺,Er³⁺ co-doped Y₂GaSbO₇ powder with multicolor luminescence. Through adjusting the excitation wavelengths, emissions in violet, blue, green, and orange are achieved. The phosphor demonstrates remarkable thermochromism due to the distinct temperature-dependent luminescence of Bi³⁺ and Er³⁺, confirmed under irradiation at 312 or 980 nm. By reducing the power of 980 nm laser or increasing the laser-to-sample distance, the emitting color can be precisely tuned from gold‒yellow or yellow‒green to orange‒red. These diverse luminescent characteristics enable the creation of a multilevel anti-counterfeiting system. Moreover, a four-mode optical thermometry with an optimal relative sensitivity of 1.98% K⁻¹, a high thermal resolution of 0.15 K, and signal reversibility was established using fluorescence intensity ratio and fluorescence decay time. These results disclose that Y₂GaSbO₇:Bi³⁺,Er³⁺ phosphor is a promising candidate for temperature monitoring and dynamic anti-counterfeiting applications.

Magneto-optical (MO) glass, which has been garnering increasing interest for its light rotation capability, often faces challenges related to valence variations, resulting in suboptimal MO performance. The composition of the glass matrix and the specifics of the melting process are crucial in determining the glass network structure and cation valence state distribution. This has led to the exploration to enhance network connectivity and introduce more Tb³⁺ ions to boost the MO performance. In this study, alkali metal oxides (Li₂O/Na₂O/K₂O) were introduced to modify the glass network structure and lower melting characteristics accordingly. Particularly noteworthy is the advantage offered by K₂O that lowers free electron density and melting temperature. Through meticulous control of the alkali metal oxide content and the melting temperature, a groundbreaking Verdet constant of 113.87 rad/(T m) at 650 nm for the 40T5K glass was accomplished. Furthermore, the MO glasses have been successfully applied in the encryption and decryption of one-dimensional text and two-dimensional images, thereby exhibiting the utility of this innovative material in information security applications.

To ensure the durability of solid oxide fuel cell sealants, the understanding of the microstructural influence on viscous crack healing is essential. To this end, the effect of microstructure with respect to the spatial distribution of filler particles on viscous crack healing was studied with confocal laser scanning microscopy in glass-matrix composites (GMCs) made by mix-milling and sintering of soda-lime magnesium silicate glass and Φ ≈ 6 vol% ZrO₂ chemically inert rigid filler particles. This way, no change in Φ occurred during the crack healing treatments studied on Vickers indentation-induced radial cracks in polished GMC surfaces. Different microstructures were mimicked using different ZrO₂ particle sizes for mix-milling. Unlike coarse ZrO₂ particles, similar in size to the glass particle, fine ZrO₂ particles, much smaller than the glass particles, form a rigid percolation framework (RPF) of ZrO₂ filler particles around the former glass particles or glass particle agglomerates. For this RPF microstructure, crack healing was observed more readily as crack healing retardation phenomena like large-scale crack widening and crack tip rounding were strongly reduced, whereas narrow cracks could still heal locally within the glassy regions.

We demonstrated the correlations between the specific temperature behavior of the colossal dielectric permittivity, unusual electro-transport characteristics, and frequency dependences of the pyroelectric response of the fine-grained ceramics prepared by the spark plasma sintering of the ferroelectric BaTiO₃ nanoparticles. The temperature dependences of the electro-resistivity indicate the frequency-dependent transition in the electro-transport mechanisms between the lower and higher conductivity states accompanied by the maximum in temperature dependence of the loss angle tangent. The pyroelectric thermal wave probing revealed the existence of the spatially inhomogeneous counter-polarized ferroelectric states at the opposite surfaces of the ceramic sample. We described the temperature behavior of the colossal dielectric response and losses using the core−shell model for ceramic grains, effective medium approximation, and Maxwell−Wagner approach.

Ceramic thermal barrier coating (TBC) materials are used to protect the superalloys from the damage of harmful high-temperature airflow and improve the efficiency of jet and gas turbine engines. However, the long-term application of TBC materials and the robustness of these materials can be destroyed by aggressive calcium-magnesium-alumina-silicate (CMAS) melt during high-temperature service. Increasing the configuration entropy of material by doping multiple principal components has become a research hotspot in the design of corrosion-resistant thermal barrier coating material and has opened an infinite space of chemical composition, structure, and material properties. In this study, high-entropy (La_0.2Sm_0.2Er_0.2Y_0.2Yb_0.2)₂Ce₂O₇ was synthesized and its CMAS corrosion behavior was investigated by experimental investigation and first-principles calculation. The effects of the increase of configurational entropy and the subsequent potential effects on the CMAS corrosion behavior of Ce-based fluorite oxides have been sufficiently investigated. By compared with control samples, the high-entropy (La_0.2Sm_0.2Er_0.2Y_0.2Yb_0.2)₂Ce₂O₇ possesses the minimum infiltration depth of CMAS melts and the denser corrosion reaction layer, indicating the best corrosion resistance. The corrosion resistance mechanism of high-entropy (La_0.2Sm_0.2Er_0.2Y_0.2Yb_0.2)₂Ce₂O₇ was studied by first-principles calculation. The greater stability and resistance to segregation of CMAS melt in the CMAS/(La_0.2Sm_0.2Er_0.2Y_0.2Yb_0.2)₂Ce₂O₇ system, the poor adsorption capacity for CMAS melt which leads to a weak infiltration ability of CMAS melt; the weakest interfacial chemical reaction at the interface indicated by the smallest value of Griffith rupture work and the least species migration of high-entropy fluorite oxide can be responsible to the enhanced corrosion resistance. Our work reveals that increasing the configuration entropy can be an effective strategy for TBC material to enhance corrosion resistance.