Search Results (161)

Chemiresistive gas sensors are extensively employed in environmental monitoring, disease diagnostics, and industrial safety due to their high sensitivity, low cost, and miniaturization. However, the high cross-sensitivity and poor selectivity of gas sensors limit their practical applications in complex environmental detection. In particular, the mechanisms underlying the selective response of certain chemiresistive materials to specific gases are not yet fully understood. In this review, we systematically discuss material design strategies and system integration techniques for enhancing the selectivity and sensitivity of gas sensors. The focus of material design primarily on the modification and optimization of advanced functional materials, including semiconductor metal oxides (SMOs), metallic/alloy systems, conjugated polymers (CPs), and two-dimensional nanomaterials. This study offers a comprehensive investigation into the underlying mechanisms for enhancing the gas sensing performance through oxygen vacancy modulation, single-atom catalysis, and heterojunction engineering. Furthermore, we explore the potential of emerging technologies, such as bionics and artificial intelligence, to synergistically integrate with functional sensitive materials, thereby achieving a significant enhancement in the selectivity of gas sensors. This review concludes by offering recommendations aimed at improving the selectivity of gas sensors, along with suggesting potential avenues for future research and development. Full article

Uncooled microbolometers play a pivotal role in infrared detection owing to their compactness, low power consumption, and cost-effectiveness. This review comprehensively summarizes recent progress in thermistor materials and focal plane arrays (FPAs), highlighting improvements in sensitivity and integration. Vanadium oxide (VO_x) remains predominant, with Al-doped films via atomic layer deposition (ALD) achieving a temperature coefficient of resistance (TCR) of −4.2%/K and significant 1/f noise reduction when combined with single-walled carbon nanotubes (SWCNTs). Silicon-based materials, such as phosphorus-doped hydrogenated amorphous silicon (α-Si:H), exhibit a TCR exceeding −5%/K, while titanium oxide (TiO_x) attains TCR values up to −7.2%/K through ALD and annealing. Emerging materials including GeSn alloys and semiconducting SWCNT networks show promise, with SWCNTs achieving a TCR of −6.5%/K and noise equivalent power (NEP) as low as 1.2 mW/√Hz. Advances in FPA technology feature pixel pitches reduced to 6 μm enabled by vertical nanotube thermal isolation, alongside the 3D heterogeneous integration of single-crystalline Si-based materials with readout circuits, yielding improved fill factors and responsivity. State-of-the-art VO_x-based FPAs demonstrate noise equivalent temperature differences (NETD) below 30 mK and specific detectivity (D*) near 2 × 10¹⁰ cm⋅Hz ^1/2/W. Future advancements will leverage materials-driven innovation (e.g., GeSn/SWCNT composites) and process optimization (e.g., plasma-enhanced ALD) to enable ultra-high-resolution imaging in both civil and military applications. This review underscores the central role of material innovation and system optimization in propelling microbolometer technology toward ultra-high resolution, high sensitivity, high reliability, and broad applicability. Full article

The microcrack initiation and evolution behavior of Fe-C alloy under uniaxial tensile loading are investigated using molecular dynamics (MD) simulations. The model is stretched along the z-axis at a strain rate of 2 × 10⁹ s⁻¹ and temperatures ranging from 300 to 1100 K, aiming to elucidate the microscopic deformation mechanisms during crack evolution under varying thermal conditions. The results indicate that the yield strength of Fe-C alloy decreases with a rising temperature, accompanied by a 25.2% reduction in peak stress. Within the temperature range of 300–700 K, stress–strain curves exhibit a dual-peak trend: the first peak arises from stress-induced transformations in the internal crystal structure, while the second peak corresponds to void nucleation and growth. At 900–1100 K, stress curves display a single-peak pattern, followed by rapid stress decline due to accelerated void coalescence. Structural evolution analysis reveals sequential phase transitions: initial BCC-to-FCC and -HCP transformations occur during deformation, followed by reversion to BCC and unidentified structures post-crack formation. Elevated temperatures enhance atomic mobility, increasing the proportion of disordered/unknown structures and accelerating material failure. Higher temperatures promote faster potential energy equilibration, primarily through accelerated void growth, which drives rapid energy dissipation. Full article

Mixing enthalpy (ΔH_mix), mixing entropy (ΔS_mix), atomic-size difference (δ), and valence electron concentration (VEC) are the indicators determining the phase structures of multi-principal element alloys. Exploring the relationships between the structures and properties of multi-principal element films is a fundamental study. TiZrHf films with a ΔH_mix of 0.00 kJ/mol, ΔS_mix of 9.11 J/mol·K (1.10R), δ of 3.79%, and VEC of 4.00 formed a hexagonal close-packed (HCP) solid solution. Exploring the characterization of TiZrHf films after solving Ta, Y, and Cr atoms with distinct atomic radii is crucial for realizing multi-principal element alloys. This study fabricated TiZrHf, TiZrHfTa, TiZrHfY, and TiZrHfCr films through co-sputtering. The results indicated that TiZrHfTa films formed a single body-centered cubic (BCC) solid solution. In contrast, TiZrHfY films formed a single HCP solid solution, and TiZrHfCr films formed a nanocrystalline BCC solid solution. The crystallization of TiZrHf(Ta, Y, Cr) films and the four indicators mentioned above for multi-principal element alloy structures were correlated. The mechanical properties and thermal stability of the TiZrHf(Ta, Y, Cr) films were investigated. Full article

In this work, the W element, with a larger atomic radius compared to Co, Fe, and Ni, was added to modify the microstructure and enhance the yield strength of CoFeNi medium entropy alloy (MEA). A detailed study was conducted to clarify the effects of W additions and annealing temperatures on the microstructure evolution and mechanical properties of CoFeNiW_x (x = 0, 0.1, and 0.3) MEAs. CoFeNiW_0.1 retained a single FCC structure without the formation of precipitates in the FCC phase, indicating that W, with a larger atomic radius, can completely dissolve in CoFeNiW_0.1. For CoFeNiW_0.3 MEA, coarse particles with an average diameter of ~2 μm appeared after homogenizing. Nevertheless, when the alloy was annealed at 800 °C and 900 °C, fine particles formed, with the average diameters of approximately 144 nm and 225 nm, respectively. After annealing at 800 °C, the CoFeNiW_0.3 with a partially recrystallized microstructure exhibited better comprehensive mechanical properties. Full article

This study presents the design and microstructural investigation of a single-crystal (SX) Re-bearing high-entropy superalloy (HESA-X1) featuring a thermally stable γ–γ′–γ hierarchical microstructure. The alloy exhibits FCC γ nanoparticles embedded within L1₂-ordered γ′ precipitates, themselves distributed in a γ matrix, with the suppression of detrimental topologically close-packed (TCP) phases. To elucidate solidification behavior and phase stability, Scheil–Gulliver and TC-PRISMA simulations were conducted alongside SEM and XRD analyses. Near-atomic scale analysis in 3D using Atom Probe Tomography (APT) revealed pronounced elemental partitioning, with Re strongly segregating to the γ matrix, while Al and Ti were preferentially enriched in the γ′ phase. Notably, Re demonstrated a unique partitioning behavior compared to conventional superalloys, facilitating the formation and stabilization of γ nanoparticles during two-step aging (Ag-2). These γ nanoparticles significantly contribute to improved mechanical properties. Long-term aging (up to 200 h) at 750–850 °C confirmed exceptional phase stability, with minimal coarsening of γ′ and retention of γ nanoparticles. The coarsening rate constant K of γ′ at 750 °C was significantly lower than that of Re-free HESA, confirming the diffusion-suppressing effect of Re. These findings highlight critical roles of Re in enhancing microstructural stability by reducing atomic mobility, enabling the development of next-generation HESAs with superior thermal and mechanical properties for high-temperature applications. Full article

Ceramic dental prosthetics with internal metal structures are made from a cobalt–chromium alloy that is coated with ceramic. This study aims to validate surface treatments for the metal that enhance the adhesion of the ceramic coating under masticatory forces. Surface conditioning is performed using mechanical methods, like sandblasting (SB), and thermal methods, such as oxidation (O). The ceramic coating is applied to the metal component following the conditioning process, which can be conducted using either a single method or a combination of methods. Each conditioned sample undergoes characterization through various techniques, including drop shape analysis (DSA), scanning electron microscopy (SEM), X-ray diffraction (EDX), and atomic force microscopy (AFM). After the ceramic coating is applied and subjected to thermal sintering, the metal–ceramic samples are mechanically tested to assess the adhesion of the ceramic layer. The research findings, illustrated by scanning electron microscopy (SEM) images of the metal structures’ surfaces, indicate that alloy powder particles ranging from 10 to 50 µm were either adhered to the surfaces or present as discrete dots. Particles that exceed the initial design specifications of the structure can be smoothed out using sandblasting or mechanical finishing techniques. The energy-dispersive spectroscopy (EDS) results show that, after sandblasting, fragments of aluminum oxide remain trapped on the surface of the metal structures. These remnants are considered impurities, which can negatively impact the adhesion of the ceramic to the metal substrate. The analysis focuses on the exfoliation of the ceramic material from the deformed metal surfaces. The results emphasize the significant role of the sandblasting method and the micro-topography it creates, as well as the importance of the oxidation temperature in the treatment process. Drawing on 25 years of experience in dental prosthetics and the findings from this study, this publication aims to serve as a guide for applying the ceramic bonding layer to metal surfaces and for conditioning methods. These practices are essential for enhancing the adhesion of ceramic materials to metal substrates. Full article

TbCu₇-type Sm-based compounds can be produced in bulk and potentially surpass Nd₂Fe₁₄B as permanent magnets. However, as the processes to prepare anisotropic magnetic particles are limited, the full potential of TbCu₇-type Sm-based compounds cannot be exploited. In this study, metastable TbCu₇-type phases of anisotropic Sm–Fe–N ultrafine particles were prepared using the low-oxygen induction thermal plasma (LO-ITP) process. X-ray diffraction analysis revealed that the obtained TbCu₇-type Sm–Fe alloy nanoparticles exhibited a c/a value of 0.8419, with an Fe/Sm atomic ratio of ~8.5. After nitrogenation, the obtained Sm–Fe–N nanoparticles were aligned under an external magnetic field, indicating that each alloy particle exhibited anisotropic magnetic properties. A substantially high degree of alignment of 91 ± 2% was achieved, quantitatively estimated via pole figure measurements. Numerical analysis following Sm–Fe nanoparticle formation showed that, compared with Fe condensation, Sm condensation persisted even at low temperatures, because of a significant difference in vapor pressure between Sm and Fe. Though this led to a relatively large compositional distribution of Sm within particles with a Sm concentration of 9–12 at%, the preparation of single-phase TbCu₇-type Sm–Fe–N particles could be facilitated by optimizing several parameters during the LO-ITP process. Full article

The cubic phase of the high-entropy alloy AgBi_1−xSb_xSe_0.8S_0.6Te_0.6 compound, characterized by the substitution of Sb for Bi in the structure to enhance phonon scattering, has been analyzed for local atomic displacements and electronic structure using a combination of X-ray absorption and X-ray photoelectron spectroscopy techniques. Notably, Ag K-edge and Bi L₃-edge X-ray absorption measurements demonstrate a contraction of bond distances upon substitution due to the smaller size of Sb. Conversely, X-ray photoelectron spectroscopy reveals that, while Ag remains predominantly in the Ag¹⁺ state across all samples, Bi and Sb exhibit a single valence state only for minimal Sb substitution. At higher Sb substitution levels, both Bi and Sb manifest mixed valence states, indicating complex electronic behavior that potentially influences the thermoelectric properties of the system. These findings suggest that optimizing the local structure through Sb substitution can be beneficial in enhancing the material’s thermoelectric performance. Full article

In polymer electrolyte membrane fuel cells (PEMFCs), substantial efforts have been made to focus on Pt and Pt alloy catalysts to enhance their catalytic performance. However, these catalysts still fail to meet practical requirements and existing PtCo catalysts face durability issues due to structural limitations. In this study, carbon-supported hybrid PtCo alloy catalysts (H-PtCo) with improved activity and durability are synthesized by reducing Co precursors onto pre-formed colloidal Pt nanoparticles. Elemental mapping via transmission electron microscopy reveals that the H-PtCo catalysts exhibit a high concentration of Co atoms near the sub-surface. This Co enrichment results from the conformal deposition of Co atoms onto Pt nanoparticles, followed by high-temperature treatment. Electrochemical characterizations, including linear sweep voltammetry (LSV) and accelerated durability test (ADT), demonstrate that the H-PtCo catalysts outperform conventional PtCo alloys (C-PtCo), synthesized via the co-reduction method of Pt and Co, in terms of oxygen reduction reaction (ORR) activity and stability. Furthermore, single-cell tests reveal that the H-PtCo catalysts significantly enhance both performance and durability compared to C-PtCo and Pt catalysts. These findings emphasize the critical role of Co atom distribution within PtCo nanoparticles in improving catalytic efficiency and long-term stability. Full article

High-entropy alloys (HEAs) represent a paradigm-shifting material system offering vast compositional space for tailoring mechanical properties. The yield strength and hardness are critical performance metrics, yet their interrelationships in diverse HEAs remain incompletely understood, partly due to data limitations. This work employs an integrated machine learning framework to investigate the compressive yield strength (σ_y) and hardness (HV) correlation across a dataset of cast HEAs. Random forest models are successfully developed for phase structure classification (accuracy = 92%), hardness prediction (test R² = 0.90), and yield strength prediction (test R² = 0.91), enabling data imputation to expand the analysis dataset. Correlation analysis on the expanded dataset reveals a general positive trend between σ_y and HV (overall Pearson r = 0.75) but highlights a strong dependence on the predicted phase structure. The single-phase BCC alloys exhibit the strongest linear correlation between σ_y and HV (r = 0.88), whereas the single-phase FCC alloys show a weaker linear dependence (r = 0.59), and multiphase alloy systems display varied behavior. The specific ranges of compositional parameters (highly negative mixing enthalpy ΔH, low atomic size difference δ, high mixing entropy ΔS, and intermediate-to-high valence electron concentration VEC) are associated with a stronger σ_y-HV correlation, potentially linked to the formation of stable solid solutions. Furthermore, artificial neural network modeling confirms the varying complexity of the σ_y-HV relationship across different phases, outperforming simple models for some multiphase systems. This work provides robust predictive models for HEA properties and advances the fundamental understanding of the composition- and phase-dependent coupling between yield strength and hardness, aiding rational HEA design. Full article

High-entropy alloys (HEAs) exhibit excellent properties such as high strength, good ductility, superior corrosion resistance, and thermal stability, making them highly promising for applications in the aerospace, energy, and automotive industries. Among them, the FeNiCrMn HEA demonstrates outstanding corrosion resistance while eliminating the expensive Co element present in the “Cantor” alloy, significantly reducing costs. However, current research on the FeNiCrMn HEA has primarily focused on its corrosion resistance, with relatively limited studies on its mechanical properties. This paper investigated the effects of different crystal orientations, temperatures, and strain rates on the mechanical properties and plastic deformation mechanisms of an equiatomic FeNiCrMn HEA using molecular dynamics simulations. The results revealed that the FeNiCrMn HEA exhibited significant anisotropy under loading along different orientations, with the maximum yield stress observed along the <11-1> direction. During the elastic stage, all crystals maintained a single FCC structure. As strain increased, yielding occurred, accompanied by a sudden drop in stress, which was attributed to the generation of dislocations. The mechanical properties of the FeNiCrMn HEA were highly sensitive to temperature variations. Elevated temperatures intensify atomic thermal vibrations, making it easier for atoms to deviate from their equilibrium positions and facilitating dislocation nucleation and movement. Consequently, the yield strength and yield strain decreased with increasing temperature. In contrast, the yield strength of the FeNiCrMn HEA was relatively insensitive to strain rate variations. Instead, the strain rate primarily affected the alloy’s flow stress. During tensile loading, higher strain rates led to higher dislocation densities. When the stress stabilized, the flow stress increased with the strain rate. These findings provide a theoretical foundation for the future development of FeNiCrMn HEAs. Full article

The electrochemical reduction of carbon dioxide (CO₂RR) utilizing intermittent electricity from renewable energy sources represents an emerging and promising approach to achieve carbon neutrality and mitigate the greenhouse effect. This review comprehensively summarizes recent advances in Cu-based metal–organic framework (MOF) electrocatalysts for CO₂RR, focusing on their applications in producing C₁ and C₂₊ products. This paper highlights key strategies such as nanostructure manipulation, multi-component tandem catalysis, single-atom alloying, and ligand functionalization to optimize the binding energies of intermediate species and promote selective CO₂RR pathways. Numerous examples are presented, showcasing remarkable Faradaic efficiencies and product selectivities achieved through rational catalyst design. Furthermore, the use of MOF-derived materials and composites with other materials, like carbon nanotubes, graphene, and metal oxides, is discussed to enhance conductivity, stability, and selectivity. Despite the significant progress, challenges remain in achieving stable and scalable catalysts with high activity and selectivity towards specific C₂₊ products. This review underscores the importance of precise control of catalyst composition, structure, and surface properties to tackle these challenges and provides valuable insights for future research directions in developing advanced Cu-based MOF electrocatalysts for practical applications in CO₂ conversion technologies. Full article

Refractory high-entropy or medium-entropy alloys (RHEAs, RMEAs) exhibit outstanding strength and hold significant promise for high-temperature applications. However, their pronounced brittleness at room temperature restricts their industrial application. Recently, the introduction of interstitial oxygen has proven effective in refining the microstructure and improving the mechanical properties of RMEAs. In this study, we investigated the effect of interstitial oxygen content ranging from 0.5 to 6 at.% on the microstructures and mechanical properties of TiZrNb MEA. The alloys display a single BCC structure, showing a dendritic crystal morphology. At an oxygen content of 4 at.%, the alloy shows a room-temperature compressive yield strength of 1300 MPa and compressive strain of over 50%, achieving a balanced strength and ductility combination. Moreover, it shows excellent high-temperature mechanical properties, with yield strength exceeding 500 MPa at 800 °C. The Toda-Caraballo and Labusch theoretical models were used in the study to clarify the strengthening mechanism of the alloys, and the theoretical yield strengths obtained by calculation coincided with the experimental yield strengths. This validation not only confirms that the primary strengthening mechanism is solid solution strengthening, but also proves the reliability of the model in predicting the mechanical properties of MEAs and provides a theoretical basis for the use of interstitial atoms to strengthen MEAs. Full article

The effects of X-doping (X = Mo, Ti, Ni) on the structure, stability, and electronic properties of B2-FeAl supercells, as well as the migration behavior of Cl atoms between interstitial sites and the corrosion behavior of FeAl coatings in molten chloride, were investigated by combining the first principles based on density functional theory (DFT) experiments. Our results confirmed that Mo and Ti atoms are more likely to replace Al atoms in B2-FeAl supercells, while Ni atoms preferentially replace Fe atoms. A single Cl atom is more inclined to be adsorbed at the tetrahedral (Tet) interstitial site of bulk B2-FeAl, and its formation energy $E_f=$− 2.504 eV, indicating that it can very easily invade FeAl alloys. (Mo, Ti, Ni) doping inhibited the diffusion of Cl atoms in the bulk B2-FeAl configuration and enhanced the corrosion resistance of the material to chlorinated molten salts, and Ti doping (overcoming the energy barrier by 0.326 eV) had the most obvious blocking effect. Based on the theoretical conclusions, this experimental study prepared an FeAl coating on 310S stainless steel with a Ni content of 20.22 wt.% at 800 °C for 15 h, which was then annealed at 900 °C for 25 h, and Ni was uniformly dissolved in the B2-FeAl phase. Subsequently, the annealed FeAl coating was corroded in molten chlorinated salts at 800 °C for 100 h, and an oxide layer with a thickness of 25–35 µm formed on the surface; the main components of this layer were Al₂O₃, NiFe₂O₄, and their solid solutions, which significantly improved the corrosion resistance of 310S stainless steel to chlorinated molten salt. Full article