Search Results (55)

The development of high-performance solid electrolytes is critical to advancing solid-state lithium-ion batteries (SSBs), with lithium lanthanum zirconium oxide (LLZO) emerging as a leading candidate due to its chemical stability and wide electrochemical window. In this study, we systematically investigated the effects of cation dopants, including aluminum (Al³⁺), tantalum (Ta⁵⁺), gallium (Ga³⁺), and rubidium (Rb⁺), on the structural, electronic, and ionic transport properties of LLZO using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. It appeared that, among all simulated results, Al-LLZO exhibits the highest ionic conductivity of 1.439 × 10⁻² S/cm with reduced activation energy of 0.138 eV, driven by enhanced lithium vacancy concentrations and preserved cubic-phase stability. Ta-LLZO follows, with a conductivity of 7.12 × 10⁻³ S/cm, while Ga-LLZO and Rb-LLZO provide moderate conductivity of 3.73 × 10⁻³ S/cm and 3.32 × 10⁻³ S/cm, respectively. Charge density analysis reveals that Al and Ta dopants facilitate smoother lithium-ion migration by minimizing electrostatic barriers. Furthermore, Al-LLZO demonstrates low electronic conductivity (1.72 × 10⁻⁸ S/cm) and favorable binding energy, mitigating dendrite formation risks. Comparative evaluations of radial distribution functions (RDFs) and XRD patterns confirm the structural integrity of doped systems. Overall, Al emerges as the most effective and economically viable dopant, optimizing LLZO for scalable, durable, and high-conductivity solid-state batteries. Full article

Stacking fault tetrahedra (SFTs) are typically considered improbable in high stacking fault energy metals like aluminum. Using molecular statics and dynamics simulations, we reveal the formation, growth, and transformation of SFTs in aluminum via vacancy aggregation. Three types—perfect, truncated, and defective SFTs—are characterized by their structure, formation energy, and binding energy across a range of vacancy cluster sizes. Formation energies of perfect and truncated SFTs follow a scaling relation; beyond a critical size, truncated SFTs become thermodynamically favored, indicating a size-dependent transformation pathway. Binding energy and structure evolution exhibit quasi-periodic behavior, where vacancies initially adsorb at the vertices or the midpoints of the edges of a perfect SFT, then aggregate along one facet, triggering fault nucleation and a binding energy jump as the system reconstructs into a new perfect SFT. Molecular dynamics simulations further confirm the SFT nucleation and growth via vacancy aggregation, consistent with thermodynamic predictions. SFTs exhibit notable thermal mobility, enabling coalescence and evolution into vacancy-type dislocation loops. BCC-like $V_5$ clusters are identified as potential nucleation precursors. These findings explain the nanoscale, low-temperature nature of SFTs in aluminum and offer new insights into defect evolution and control in FCC metals. Full article

This study addresses the efficiency and cost challenges of hydrogen evolution reaction (HER) catalysts in the context of carbon neutrality strategies by employing a synergistic approach that combines cation vacancy anchoring and transition metal doping on two-dimensional (2D) MXenes. Using an in situ LiF/HCl etching process, the aluminum layers in Ti₃AlC₂ were precisely removed, resulting in a few-layer Ti₃C₂T_x MXene with an increased interlayer spacing of 12.3 Å. Doping with the transition metals Fe, Co, Ni, and Cu demonstrated that Fe@Ti₃C₂ provided the optimal HER performance, characterized by an overpotential (η₁₀) of 81 mV at 10 mA cm⁻², a low Tafel slope of 33.03 mV dec⁻¹, and the lowest charge transfer resistance (R_ct = 5.6 Ω cm²). Mechanistic investigations revealed that Fe’s 3d⁶ electrons induce an upward shift in the d-band center of MXene, improving hydrogen adsorption free energy and reducing lattice distortion. This research lays a solid foundation for the design of non-precious metal catalysts using MXenes and highlights future avenues in bimetallic synergy and scalability. Full article

This study introduces a novel in situ pulsed current-assisted resistance spot welding method, which differs fundamentally from conventional post-weld heat treatments and is designed to enhance the mechanical performance of 7075-T651 aluminum alloy joints. Immediately after welding, a short-duration pulsed current is applied while the weld remains in a high excess-vacancy state, effectively accelerating precipitation reactions within the weld region. Transmission electron microscopy (TEM) observations reveal that pulsed current treatment promotes the formation of band-like solute clusters, indicating a significant acceleration of the early-stage precipitation process. Interestingly, the formation of quasicrystalline phases—rare in Al-Zn-Mg-Cu alloy systems—is incidentally observed at grain boundaries, exhibiting characteristic fivefold symmetry. Selected area electron diffraction (SAED) patterns further show that these quasicrystals undergo partial dissolution under the influence of the pulsed current, transforming into short-range ordered cluster-like structures. Lap shear tests demonstrate that joints treated with pulsed current exhibit significantly higher peak load and energy absorption compared to untreated specimens. Statistical analysis of weld size confirms that both groups possess comparable weld diameters under identical welding currents, suggesting that the observed mechanical improvements are primarily attributed to microstructural evolution rather than geometric factors. Full article

Stratlingite is known as one of the hydration products of aluminum-rich cements. Its microstructure and, consequently, mechanical properties, depend on the Al/Si ratio and hydration conditions. The layered structure of stratlingite is characterized as defected, with vacancies in the aluminosilicate layer. This study uses density functional theory calculations on different stratlingite models to show how chemical composition, water content, and structural defects affect its mechanical properties. The developed models represent structures with full occupancy, with little or no content of structural water, and with vacancies in the aluminosilicate layer. It was shown that the full occupancy models have the highest toughness and are strongly anisotropic. The calculated bulk modulus (B_H) of the models with full occupancy was about 40 GPa, being in the typical range for calcium aluminosilicate minerals. The water loss led to an increase in B_H by approximately 40% compared to the models with full occupancy. In contrast, the models with vacancies exhibited a decrease in B_H of about 30%. In models with the high silicon content (Al/Si ratio of 1/4), B_H, Young’s (E_H), and shear (G_H) moduli decreased in a range 15%–30% compared to the models with an Al/Si ratio of 2/3 of Al/Si. Finally, according to Pugh’s ratio (B_H/G_H), which serves as a criterion for brittle–ductile transition (1.8), the models with full occupancy exhibit a brittle behavior, whereas the defected structures are closer to ductile. This could explain the elastic behavior of stratlingite binder in concretes. Generally, the calculations showed that all investigated parameters (chemical composition, water content, and structural defects) have a significant impact on the mechanical properties of stratlingite minerals. Full article

In order to solve the self-heating problem of power electronic devices, this paper adopts a nonequilibrium molecular dynamics approach to study the thermal transport regulation mechanism of the aluminum nitride/graphene/silicon carbide heterogeneous interface. The effects of temperature, size, and vacancy defects on interfacial thermal conductivity are analyzed by phonon state density versus phonon participation rate to reveal their phonon transfer mechanisms during thermal transport. It is shown that the interfacial thermal conductance (ITC) increases about three times when the temperature increases from 300 K to 1100 K. It is analyzed that the increase in temperature will enhance lattice vibration, enhance phonon coupling degree, and thus increase its ITC. With the increase in the number of AlN-SiC layers from 8 to 28, the ITC increases by about 295.3%, and it is analyzed that the increase in the number of AlN-SiC layers effectively reduces the interfacial scattering and improves the phonon interfacial transmission efficiency. The increase in the number of graphene layers from 1 layer to 4 layers decreases the ITC by 70.3%. The interfacial thermal conductivity reaches a minimum, which is attributed to the increase in graphene layers aggravating the degree of phonon localization. Under the influence of the increase in graphene single and double vacancy defects concentration, the ITC is slightly reduced. When the defect rate reaches about 20%, the interfacial thermal conductance of SV (single vacancy) and DV (double vacancy) defects rises back to 5.606 × 10⁻² GW/m²K and 5.224 × 10⁻² GW/m²K, respectively. It is analyzed that the phonon overlapping and the participation rate act at the same time, so the heat-transferring phonons increase, increasing the thermal conductance of their interfaces. The findings provide theoretical support for optimizing the thermal management performance of heterostructure interfaces. Full article

Thermally grown oxide (TGO) layers—primarily alumina (Al₂O₃)—provide oxidation resistance and high-temperature protection for thermal barrier coatings. However, during their service in humid and hot environments, water vapor accelerates TGO degradation by stabilizing metastable alumina phases (e.g., θ-Al₂O₃) and inhibiting their transformation to the thermodynamically stable α-Al₂O₃, a phenomenon which has been shown in numerous experimental studies. However, the microscopic mechanisms by which water vapor affects the phase stability and transformation of alumina remain unresolved. This study employs first-principles calculations to investigate hydrogen’s role in altering vacancy formation, aggregation, and atomic migration in θ- and α-Al₂O₃. The results reveal that hydrogen incorporation reduces the formation energies for aluminum and oxygen vacancies by up to 40%, promoting defect generation and clustering; increases aluminum migration barriers by 25–30% while lowering oxygen migration barriers by 15–20%, creating asymmetric diffusion kinetics; and stabilizes oxygen-deficient sublattices, disrupting the structural reorganization required for θ- to α-Al₂O₃ transitions. These effects collectively sustain metastable θ-Al₂O₃ growth and delay phase stabilization. By linking hydrogen-induced defect dynamics to macroscopic coating degradation, this work provides atomic-scale insights for designing moisture-resistant thermal barrier coatings through the targeted inhibition of vacancy-mediated pathways. Full article

The influence of Mg doping in α-Al₂O₃ crystals is investigated in this article by first-principles calculations and formation energies, density of states, and computed absorption spectra. Three models related to Mg²⁺ substituting for Al³⁺ doping structures were constructed, as well as spinel structure models with varying aluminum-magnesium ratios. The formation energy calculations confirmed the rationality of the Mg_AlV_O model, which means that Mg substitutional doping incorporating oxygen vacancies is most likely to form in crystals. The combined action of magnesium and oxygen vacancies introduced new defect energy levels in the bandgap. The calculated absorption spectra of the Mg_AlV_O and Mg-rich spinel structures exhibited various color centers. The experimental absorption spectra and thermoluminescence characteristics of α-Al₂O₃:Mg and alumina-magnesium (Al-Mg) spinel crystal samples were tested. The thermoluminescence peak of the Al-Mg spinel was significantly stronger than that of the α-Al₂O₃:Mg crystal. The consistency between the model-calculated absorption spectra and the experimental results confirmed the theoretical predictions. Based on the experimental and computational results, the influence of Mg²⁺ substitutional doping in α-Al₂O₃ and the impact of the locally Mg-rich spinel on the optical and radiation performance of α-Al₂O₃:Mg crystals are elucidated. Full article

The 7000 series aluminum alloy represented by Al-Zn-Mg-Cu has good strength and toughness and is widely used in the aerospace field. However, its high Zn content results in poor corrosion resistance, limiting its application in other fields. In order to achieve the synergistic improvement of both strength and corrosion resistance, this study examines the response of strength, toughness and corrosion resistance of a high-strength aluminum alloy tail frame under aging conditions with external stresses of 135 MPa, 270 MPa and 450 MPa. The results show that with the increase in the external stress level, the strength of the alloy improves, while its corrosion resistance decreases. An optimal balance of strength, toughness and corrosion resistance is achieved at the conditions of 270 MPa-120–24 h. This phenomenon can be attributed to two main factors: first, lattice defects such as vacancy and dislocation are introduced into the stress aging process. The introduction of a vacancy makes it easier for neighboring solute atoms to migrate there. This makes the crystal precipitates more dispersed. Also, the number of precipitates in the matrix increases from 2650 to 3117, and the size is refined from 2.96 nm to 2.64 nm. At the same time, the dislocation entanglement within the crystal structure promotes the dislocation strengthening mechanism and promotes the solute atoms to have enough channels for migration. Since too many dislocations can cause the crystal to become brittle and thus reduce its strength, entangled dislocations hinder the movement of the dislocations, thereby increasing the strength of the alloy. Secondly, under the action of external force, the precipitated phase is discontinuous, which hinders the corrosion expansion at the grain boundary, thus improving the corrosion resistance of the alloy. At low-stress states, the binding force of vacancy is stronger, the precipitation free zone (PFZ) is significantly inhibited, and the intermittent distribution effect of intergranular precipitates is the most obvious. As a result, the self-corrosion current decreases from 1.508 × 10⁻⁴ A∙cm⁻² in the non-stress state to 1.999 × 10⁻⁵ A∙cm⁻², representing an order of magnitude improvement. Additionally, the maximum depth of intergranular corrosion is reduced from 274.9 μm in the non-stress state to 237.7 μm. Full article

Due to the advantages of high capacity, low working voltage, and low cost, lithium-rich manganese-based material (LMR) is the most promising cathode material for lithium-ion batteries; however, the poor cycling life, poor rate performance, and low initial Coulombic efficiency severely restrict its practical utility. In this work, the precursor Mn_2/3Ni_1/6Co_1/6CO₃ was obtained by the continuous co-precipitation method, and on this basis, different doping levels of aluminum–magnesium were applied to modify the electrode materials by high-temperature sintering. The first discharge capacity can reach 295.3 mAh·g⁻¹ for the LMR material of Li_1.40(Mn_0.666Ni_0.162Co_0.162Mg_0.005Al_0.005)O₂. The Coulombic efficiency is 83.8%, and the capacity retention rate remains at 84.4% after 300 cycles at a current density of 1 C for the Mg-Al co-doped LMR material, superior to the unmodified sample. The improved electrochemical performance is attributed to the increased oxygen vacancy and enlarged lithium layer spacing after trace magnesium–aluminum co-doping, enhancing the lithium-ion diffusion and effectively mitigating voltage degradation during cycling. Thus, magnesium–aluminum doping modification emerges as a promising method to improve the electrochemical performance of lithium-rich manganese-based cathode materials. Full article

Serrated flow effects are visible on a metal surface even after coating. Thus, they are undesirable to manufacturers and product users. To meet the expectations of the industry, research on the conditions for serrated flow occurrence in 5019 aluminum alloy was carried out and the results were collected in the current paper. Thus, the influence of the alloy initial microstructure due to different tempers as well as plastic deformation conditions, i.e., strain rate and temperature, on the alloy stress–strain behavior was determined. Two tempers were considered: the as-fabricated F-temper and the W-temper (i.e., quenched in water after annealing at 500 °C). The synergic influence of these tempers and their tensile test conditions on the serration behavior of the stress–strain curves, i.e., the stress drop and reloading time, were also determined and categorized. Structural and X-ray diffraction studies rationalized the stress–strain characteristics according to dynamic strain aging models with positron annihilation lifetime spectroscopy providing insight into the role of lattice defects (i.e., dislocations and vacancies). The map of the serrated flow domain allowed us to obtain the activation energy of the onset of the Portevin–Le Chatelier effect equal to 56 kJ/mol. It is close to the activation energy for the pipe diffusion mechanism, obtained by applying the model formulated originally for Type B stress serration. Full article

The influence of grain size on the corrosion behavior of pure aluminum and the defect density and diffusion coefficient of surface passive films were investigated using electron backscatter diffraction (EBSD) and electrochemical testing techniques, based on the point defect model (PDM). Samples with three different grain sizes (23 ± 11, 134 ± 52, and 462 ± 203 μm) were obtained by annealing at different temperatures and times. The polarization curves and electrochemical impedance spectroscopy results for the pure aluminum in the 3.5% NaCl solution showed that with decreasing grain size, the corrosion current (i_corr) decreased monotonously, giving rise to a noble corrosion potential and a large polarization resistance. The Motte–Schottky results showed that the passive films that formed on pure aluminum with fine grains of 23 ± 11 μm had a low density (3.82 × 10²⁰ cm⁻³) of point defects, such as oxygen vacancies and/or metal interstitials, and a small diffusion coefficient (1.94 × 10⁻¹⁷ cm²/s). The influence of grain size on corrosion resistance was discussed. This work demonstrated that grain refinement could be an effective approach to achieving high corrosion resistance of passive metals. Full article

Anodic aluminum oxide (AAO) has been widely applied for the surface protection of electronic component packaging through a pore-sealing process, with the enhanced hardness value reaching around 400 Vickers hardness (HV). However, the traditional AAO fabrication at 0~10 °C for surface protection takes at least 3–6 h for the reaction or other complicated methods used for the pore-sealing process, including boiling-water sealing, oil sealing, or salt-compound sealing. With the increasing development of nanostructured AAO, there is a growing interest in improving hardness without pore sealing, in order to leverage the characteristics of porous AAO and surface protection properties simultaneously. Here, we investigate the effect of voltage on hardness under the same AAO thickness conditions in oxalic acid at room temperature from a normal level of 40 V to a high level of 100 V and found a positive correlation between surface hardness and voltage. The surface hardness values of AAO formed at 100 V reach about 423 HV without pore sealing in 30 min. By employing a hybrid pulse anodization (HPA) method, we are able to prevent the high-voltage burning effect and complete the anodization process at room temperature. The mechanism behind this can be explained by the porosity and photoluminescence (PL) intensity of AAO. For the same thickness of AAO from 40~100 V, increasing the anodizing voltage decreases both the porosity and PL intensity, indicating a reduction in pores, as well as anion and oxygen vacancy defects, due to rapid AAO growth. This reduction in defects in the AAO film leads to an increase in hardness, allowing us to significantly enhance AAO hardness without a pore-sealing process. This offers an effective hardness enhancement in AAO under economically feasible conditions for the application of hard coatings and protective films. Full article

Ultra-thin ZnO thin-film transistors with a channel thickness of <10 nm have disadvantages of a high threshold voltage and a low carrier mobility due to a low carrier concentration. Although these issues can be addressed by utilizing the strong reducing power of tri-methyl-aluminum, a method is required to control parameters such as the threshold voltage. Therefore, we fabricated a ZnO/Al₂O₃ thin-film transistor with a thickness of 6 nm and adjusted the threshold voltage and carrier mobility through the modulation of carrier generation by varying the growth temperature of Al₂O₃. As the growth temperature of Al₂O₃ increased, oxygen vacancies generated at the hetero–oxide interface increased, supplying a free carrier into the channel and causing the threshold voltage to shift in the negative direction. The optimized device, a ZnO/Al₂O₃ thin-film transistor with a growth temperature of 140 °C, exhibited a μ_sat of 12.26 cm²/V∙s, V_th of 8.16 V, SS of 0.65 V/decade, and I_ON/OFF of 3.98 × 10⁶. X-ray photoelectron spectroscopy was performed to analyze the properties of ZnO/Al₂O₃ thin films. Full article

This study comprehensively investigates Al₂O₃′s mechanical properties, focusing on fracture toughness, surface energy, Young’s modulus, and crack propagation. The density functional theory (DFT) is employed to model the vacancies in Al₂O₃, providing essential insights into this material’s structural stability and defect formation. The DFT simulations reveal a deep understanding of vacancy-related properties and their impact on mechanical behavior. In conjunction with molecular dynamics (MD) simulations, the fracture toughness and crack propagation in Al₂O₃ are explored, offering valuable information on material strength and durability. The surface energy of Al₂O₃ is also assessed using DFT, shedding light on its interactions with the surrounding environment. The results of this investigation highlight the significant impact of oxygen vacancies on mechanical characteristics such as ultimate strength and fracture toughness, drawing comparisons with the effects observed in the presence of aluminum vacancies. Additionally, the research underscores the validation of fracture toughness outcomes derived from both DFT and MD simulations, which align well with findings from established experimental studies. Additionally, the research underscores the validation of fracture toughness outcomes derived from DFT and MD simulations, aligning well with findings from established experimental studies. The combination of DFT and MD simulations provides a robust framework for a comprehensive understanding of Al₂O_3′s mechanical properties, with implications for material science and engineering applications. Full article