Search Results (115)

This study investigates the effects of different tungsten (W) doping contents on the optical transmittance, surface roughness, residual stress, and microstructure of evaporated vanadium dioxide (VO₂) thin films. W-doped VO₂ thin films with varying tungsten concentrations were fabricated using electron beam evaporation combined with ion-assisted deposition techniques, and deposited on silicon wafers and glass substrates. The optical transmittances of undoped and W-doped VO₂ thin films were measured by UV/VIS/NIR spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The root mean square surface roughness was measured using a Linnik microscopic interferometer. The residual stress in various W-doped VO₂ films was evaluated using a modified Twyman–Green interferometer. The surface morphological and structural characterization of the W-doped VO₂ thin films were performed by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Raman spectroscopy was used to analyze the structure and vibrational modes of different W-doped VO₂ thin films. These results show that the addition of tungsten significantly alters the structural, optical, and mechanical properties of VO₂ thin films. 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

Tungsten-doped vanadium dioxide (W-VO₂) shows semiconductor-to-metal phase transition properties at room temperature, which is an ideal thermo-chromic smart window material. However, low visual transmittance and solar modulation limit its application in building energy saving. In this paper, a W-VO_2−x@AA core-shell nanoparticle is proposed to improve the thermo-chromic performance of W-VO₂. Oxygen vacancies were used to promote the connection of W-VO_2−x nanoparticles with L-ascorbic acid (AA) molecules. Oxygen vacancies were tuned in W-VO₂ nanoparticles by thermal annealing temperatures in vacuum, and W-VO_2−x@AA nanoparticles were synthesized by the hydrothermal method. A smart window was formed by dispersing W-VO_2−x@AA core-shell nanoparticles into PVP evenly and spin-coating them on the surface of glass. The visual transmittance of this smart window reaches up to 67%, and the solar modulation reaches up to 12.1%. This enhanced thermo-chromic performance is related to the electron density enhanced by the AA surface molecular coordination effect through W dopant and oxygen vacancies. This work provides a new strategy to enhance the thermo-chromic performance of W-VO₂ and its application in the building energy-saving field. Full article

This study explores the development of aluminum-doped MgV₂O₄ spinel cathodes for aqueous zinc-ion batteries (AZIBs), addressing the challenges of poor Zn²⁺ ion diffusion and structural instability. Al³⁺ ions were pre-inserted into the spinel structure using a sol-gel method, which enhanced the material’s structural stability and electrical conductivity. The doping of Al³⁺ mitigates the electrostatic interactions between Zn²⁺ ions and the cathode, thereby improving ion diffusion and facilitating efficient charge/discharge processes. While pseudocapacitive behavior plays a dominant role in fast charge storage, the diffusion of Zn²⁺ within the bulk material remains crucial for long-term performance and stability. Our findings demonstrate that Al-MgV₂O₄ exhibits enhanced Zn²⁺ diffusion kinetics and robust structural integrity under high-rate cycling conditions, contributing to its high electrochemical performance. The Al-MgVO cathode retains a capacity of 254.3 mAh g⁻¹ at a high current density of 10 A g⁻¹ after 1000 cycles (93.6% retention), and 186.8 mAh g⁻¹ at 20 A g⁻¹ after 2000 cycles (90.2% retention). These improvements, driven by enhanced bulk diffusion and the stabilization of the crystal framework through Al³⁺ doping, make it a promising candidate for high-rate energy storage applications. Full article

Nanostructured binary metal oxides have demonstrated the potential for increased electrochemical performance due to their structural stability, electronic conductivity, and various oxidation states. The Li₄Ti₅O₁₂ was successfully synthesized via a hydrothermal procedure at different reaction periods (12, 18, and 24 h), and its microstructural and supercapacitive characteristics were studied. The XRD and XPS studies confirm the formation of Li₄Ti₅O₁₂ in pure phase when synthesized at 24 h (LTO@24) of reaction time. FESEM and HRTEM images reveal nanoflake surface morphology. Both LTO@24 and V-LTO@24 nanoflakes exhibited impressive electrochemical performance, with specific capacitance values of 357 and 442 F g^−1, respectively, at 1 A g⁻¹. The V-LTO@24 showed remarkable supercapacitor properties, demonstrating excellent rate capability and cycleability that surpass those of pure LTO@24. Full article

Lithium-rich layered oxide (LLO) has received extensive attention from researchers due to its high initial discharge capacity (≥250 mAh g⁻¹). However, defects such as its high initial irreversible capacity, voltage decay, and poor rate performance have severely limited its commercialization. These issues arise because the Li₂MnO₃ component in LLO is activated during the initial cycle, leading to the participation of lattice oxygen anions (O²⁻) in redox reactions. This results in irreversible oxygen loss (O₂) and subsequent structural phase transitions. To address these challenges, this study focuses on Li₁.₂Ni₀.₁₃Co₀.₁₃Mn₀.₅₄O₂ as the host material, utilizing abundant exposed (010) plane secondary particles and employing a vanadium (V) doping strategy to enhance electrochemical performance. The V forms strong V-O bonds with the lattice oxygen, effectively suppressing irreversible oxygen loss and improving structural stability. The results demonstrate that the LLO achieves the best electrochemical performance as the doping amount is 1 mol%, and the capacity retention improves from 74.5% (undoped) to 86% (V-doped) after 140 cycles at 0.5 C. Full article

Refractory metal-based Mo-Si-B alloys have long been considered the most promising candidates for replacing nickel-based superalloys in the aerospace and energy sector due to their outstanding mechanical properties and good oxidation of the Mo-silicide phases. In general, the addition of vanadium to Mo-Si-B alloys leads to a significant density reduction, while small amounts of titanium provide additional strengthening without changing the phase evolution within the Mo_ss-Mo₃Si-Mo₅SiB₂ phase field. In this work, high-energy ball milling studies on Mo-40V-9Si-8B, substituting both molybdenum and vanadium with 2 and 5 at. % Ti in all constituents, were performed to evaluate the potential milling parameters and investigate the effects of Ti doping on the milling characteristics and phase formation of these multicomponent alloys. After different milling durations, the powders were analysed with regard to their microstructure, particle size, oxygen concentration and microhardness. After heat treatment, the silicide phases (Mo,V)₃Si and (Mo,V)₅SiB₂ precipitated homogeneously within a (Mo,V) solid solution matrix phase. Thermodynamic phase calculations using the CALPHAD method showed good agreement with the experimental phase compositions after annealing, confirming the stability of the observed microstructure. Full article

Vanadium pentoxide (V₂O₅) has attracted considerable interest owing to its unique chemical and physical properties. However, traditional synthesis methods are often time-consuming, complex, and difficult to scale, limiting the broader applications of V₂O₅. Herein, we present a flame vapor deposition (FVD) method to enable rapid, scalable, and one-step synthesis of various V₂O₅ nanostructures under ambient pressure conditions. By optimizing critical synthesis parameters, specifically, source temperature (840 °C) and substrate temperature (610 °C), we achieved highly crystalline, one-dimensional (1D) V₂O₅ nanorods on a variety of substrates, including silicon (Si), fluorine tin doped (FTO) glass, stainless steel, and silicon dioxide (SiO₂). Moreover, we demonstrate the rapid growth of ultrathin, two-dimensional (2D) V₂O₅ nanoflakes with nanometer-scale thickness, as well as enhanced uniformity and coverage density with an externally applied electric field. This FVD method provides a simple, efficient, and scalable approach for synthesizing advanced V₂O₅ nanostructures, significantly expanding opportunities for their integration into various technological applications. Full article

The production of formic acid (FA) from lignocellulose and its derived sugars represents a pivotal upgrading reaction in biorefinery. This work prepared a Mn-Mo doped carbon nanotube composite catalyst for the catalytic oxidation of glucose into FA in an O₂ atmosphere, under extremely low Mn (3.27%) and Mo (0.40%) loading conditions, displaying a comparable performance with the traditional vanadium-based catalyst suffering from toxicity issues. It was confirmed that the doping of Mo led to the formation of MnMoO_X and increased the contents of low-valence Mn species (Mn²⁺ + Mn³⁺), lattice oxygen (O_latt), and surface adsorbed oxygen (O_ads) based on various characterization methods, such as XRD, XPS, TEM and ICP, which were beneficial to improve the catalytic performance. The maximum FA yield of 58.8% could be achieved over Mn₉Mo₁O_X@MWCNT after reaction for 6 h at 140 °C, which was far more than that obtained with undoped MnO_X@MWCNT (14.5%) at the identical conditions. Glyoxylic acid and arabinose were identified as two main intermediates, suggesting that the transformation of glucose into FA over Mn₉Mo₁O_X@MWCNT involved two different paths. This work proved that manganese-based catalyst was a green alternative for upgrading lignocellulose via catalytic oxidation. Full article

This study details the manufacture of vanadium-doped ZnS thin films via a cost-effective spray pyrolysis technique at varying concentrations of vanadium (4, 8, and 12 wt.%). The XRD data demonstrate the hexagonal structure of the vanadium-doped ZnS layers. The analysis of their structural properties indicates that the crystallite size (D) of the vanadium-doped ZnS films decreased as the vanadium concentration rose. The strain and dislocation density of the analyzed films were enhanced by increasing the vanadium content from 4 to 12 wt.%. The linear optical results of the vanadium-doped ZnS films revealed that the refractive index values were improved from 2.31 to 3.49 by increasing the vanadium concentration in the analyzed samples. Further, the rise in vanadium content enhanced the absorption coefficient. The energy gap (Eg) study indicates that the vanadium-doped ZnS films exhibited direct optical transitions, with the Eg values diminishing from 3.74 to 3.15 eV as the vanadium concentration increased. The optoelectrical analysis shows that the rise in vanadium concentration increases the dispersion energy from 9.48 to 12.76 eV and reduces the oscillator energy from 3.69 to 2.17 eV. The optical carrier concentration of these layers was improved from 1.49 × 1053 to 2.15 × 1053, while the plasma frequency was decreased from 4.34 × 1013 to 3.67 × 1013 by boosting the vanadium concentration from 4 to 12 wt.%. Simultaneously, the increase in vanadium content improves the nonlinear optical parameters of the vanadium-doped ZnS films. The hot probe method identifies these samples as n-type semiconductors. The findings suggest that these samples serve as an innovative window layer. Full article

V-doped ZrO₂ support materials were synthesized through a hydrothermal method, followed by a deposition–precipitation process to load Au clusters using an H₄AuClO₄ precursor. This study investigated the impact of vanadium doping on propylene epoxidation over the corresponding Au-supported catalysts. Vanadium incorporation significantly enhanced propylene conversion and promoted acrolein production, leading to reduced propylene oxide selectivity. Propylene epoxidation at higher temperatures accelerated the decomposition of oxygenates into CO₂. Vanadium addition to ZrO₂ altered the interactions between Au and V-doped ZrO₂, thereby modifying the chemical states of Zr, Au, and V and forming surface oxygen vacancies and active oxygen species. These changes defined the catalytic performance of the materials. Full article

The peroxymonosulfate (PMS)-assisted photocatalytic process has shown considerable potential for the treatment of wastewater. g-C₃N₄-based catalysts are widely applied to eliminate organic pollutants in wastewater. However, the bulk catalyst prepared by dicyandiamide has the drawback of a low surface area (10 m²/g), while the porous catalyst prepared by urea suffers from a low catalyst yield based on urea (3.5%). To address these challenges, a porous V-doped carbon nitride (V/CN) was designed through one-step thermal polymerization using urea and dicyandiamide as the carbon nitride precursor and NH₄VO₃ as the V precursor. When the ratio of urea to dicyandiamide was 10:1, the yield of V/CN was improved, while it maintained a rich porous structure with a specific surface area (64.6 m²/g). The synergetic effect of V doping and nanosheet and hollow tubular structures facilitated the separation of photogenerated carriers, leading to boosting the photocatalytic activity of g-C₃N₄ in the PMS system. V/CN(10:1) could completely degrade CBZ within 20 min, exhibiting an equivalent catalytic efficiency comparable to that of V/CN prepared by urea (V/UCN), while markedly surpassing both V/DCN and CN prepared by urea alone (UCN) in performance. This study presents an economical and effective approach for the photocatalytic degradation of pharmaceutical pollutants in aquatic environments. Full article

X-ray diffraction analysis of the pseudo-binary SrFe_1−xV_xO_3−δ system showed that the solid solution formation limit at atmospheric oxygen pressure corresponds to x ≈ 0.1. SrFe_0.9V_0.1O_3−δ has a cubic perovskite-type structure with the Pm$\overline{3}$m space group. The oxygen nonstoichiometry variations in SrFe_0.9V_0.1O_3−δ, measured by coulometric titration in the oxygen partial pressure range of 10⁻²¹ to 0.5 atm at 1023–1223 K, can be adequately described using an ideal solution approximation with V⁵⁺ as the main oxidation state of vanadium cations. This approach was additionally validated by statistical thermodynamic modeling. The incorporation of vanadium decreases both oxygen deficiency and the average iron oxidation state with respect to undoped SrFeO_3−δ. As a result, the electrical conductivity, thermal expansion and chemical expansivity associated with the oxygen vacancy formation all become lower compared to strontium ferrite. At 923 K, the conductivity of SrFe_0.9V_0.1O_3−δ is 14% lower than that of SrFeO_3−δ but 21% higher compared to SrFe_0.9Ta_0.1O_3−δ. The area-specific polarization resistance of the porous SrFe_0.9V_0.1O_3−δ electrode deposited onto 10 mol.% scandia- and 1 mol.% yttria-co-stabilized zirconia solid electrolyte with a protective Ce_0.9Gd_0.1O_2−δ interlayer, was 0.34 Ohm×cm² under open-circuit conditions at 1173 K in air. Full article

The ability to treat the surface of an object with coatings that counteract the change in radiance resulting from the object’s blackbody emission can be very useful for applications requiring temperature-independent radiance behavior. Such a response is difficult to achieve with most materials except when using phase-change materials, which can undergo a drastic change in their optical response, nullifying the changes in blackbody radiation across a narrow range of temperatures. We report on the theoretical design, giving the possibility of extending the temperature range for temperature-independent radiance coatings by utilizing multiple layers, each comprising a different phase-change material. These designed multilayer coatings are based on thin films of samarium nickelate, vanadium dioxide, and doped vanadium oxide and cover temperatures ranging from room temperature to up to 140 °C. The coatings are numerically engineered in terms of layer thickness and doping, with each successive layer comprising a phase-change material with progressively higher transition temperatures than those below. Our calculations demonstrate that the optimized thin film multilayers exhibit a negligible change in the apparent temperature of the engineered surface. These engineered multilayer films can be used to mask an object’s thermal radiation emission against thermal imaging systems. Full article

After the deposition process, the lattice structure of doped germanium remains low. Post-processing annealing reorders the structure and increases the output parameters. Thin films of germanium doped with gold (Ge:Au) and vanadium (Ge:V) were magnetron-sputtered on glass substrates. The course of the activation process was monitored in situ. Two different methods of post-processing thermal activation of the films were studied. The first method was to place the structure at an elevated temperature for a specified period of time. The second method involved placing the structure on a heating table and cycling the heating and cooling several times from room temperature to about 823 K. Both methods fulfill their function well. The differences come down to research aspects. The best thermoelectric parameters were achieved for germanium doped with 0.95 at.% vanadium. The Seebeck coefficient of 212 μV/K and the power factor of 1.24 mW·m⁻¹·K⁻² were obtained at 500 K. Full article