Applied Physics A最新文献

In this study, pristine and Fe-doped ZnO nanostructures (2–6 vol% Fe) were synthesized via the co-precipitation method and labelled as Zn@2Fe, Zn@4Fe, and Zn@6Fe. XRD analysis confirmed the formation of polycrystalline ZnO with a hexagonal wurtzite structure. FESEM and HRTEM revealed well-defined, uniformly distributed hexagonal nanorods, which exhibited superior crystallinity and surface morphology. FTIR confirmed the effective integration of Fe³⁺ into the ZnO crystal lattice, while UV–Vis spectroscopy showed a blueshift and band gap widening from 3.41 eV (pure ZnO) to 3.16 eV (Zn@2Fe). BET analysis indicated increased surface area and porosity upon Fe doping, enhancing gas adsorption capacity. Among the samples, Zn@2Fe exhibited the best NO₂ sensing performance, with a maximum response of 6.5 at 180 °C, demonstrating good selectivity, stability, and rapid response-recovery time. The sensor showed a linear response over the 1–20 ppm NO₂ range and maintained consistent performance across multiple cycles. The enhanced sensing properties are attributed to increased surface reactivity, the formation of oxygen vacancies, and Fe³⁺/Fe²⁺ redox interactions. These results establish Zn@2Fe as a promising material for high-performance NO₂ gas sensors.

Graphical Abstract

This study investigates the complex heat transfer phenomena associated with the melting process in a ferromagnetic Carreau fluid, a topic that combines multiple nonlinear physical effects rarely addressed together. The Carreau fluid model effectively captures the non-Newtonian rheological behavior exhibited by various engineering and industrial materials, while the ferromagnetic property introduces additional control over the flow and thermal transport characteristics through externally applied magnetic fields. The combination of these effects gives rise to intricate patterns of motion, heat transfer, and mass transport that are of profound importance in advanced cooling systems, material processing, and magnetic field-assisted manufacturing technologies. The novelty of the present formulation lies in the simultaneous inclusion of melting and solute stratification phenomena within a ferromagnetic Carreau fluid framework, a coupling that has not been explored in previous studies. By incorporating both melting heat transfer and solute concentration gradients, this study introduces a new multi-physics model that captures phase change energy exchange, buoyancy modification, and mass diffusion effects simultaneously offering a more realistic representation of magnetized non-Newtonian systems. To analyze this highly coupled nonlinear system, the bvp4c solver, a robust numerical method for boundary value problems, is employed to obtain accurate and stable solutions for the velocity, temperature, and concentration fields. The investigation provides deep insight into the interplay among rheology, magnetization, melting, and solute stratification, revealing how these mechanisms collectively shape the heat and mass transfer characteristics of the flow. This integrated framework not only extends the theoretical understanding of ferromagnetic Carreau fluids but also advances the field beyond existing models by providing a foundation for designing thermo-magnetic systems that exploit controlled melting and stratification effects for enhanced performance.

This study employs a MHz burst-mode femtosecond laser to induce internal modification in 350-µm-thick n-type 4 H-SiC and to demonstrate wafer slicing using a single-/double-pulse (N = 1–2) configuration under a fixed average power of 4.5 W and a burst repetition rate of 600 kHz (burst energy ≈ 7.5 µJ). Microstructure, surface topography, and residual stress were evaluated using scanning electron microscopy, laser-scanning confocal microscopy, and Raman spectroscopy. Single-pass line modification shows that N = 1–2 provide higher sub-pulse peak intensity, promoting lateral-crack formation that facilitates separation, whereas N = 3–5 drive deeper modification without lateral cracks. Raman measurements reveal a characteristic tension–compression residual-stress distribution, with tensile stress above and predominantly compressive stress below the lateral cracks; for example, at N = 2, the stresses are + 77.5 MPa (tension) and − 51.7 MPa (compression) at y = ± 4 μm. Full-area slicing experiments demonstrate that N = 2 shortens the step-like period and reduces the sliced-surface roughness from Sz = 47.8 μm to 32.2 μm, while maintaining a tensile strength of 3.4 MPa. Comparative Raman analysis of the two sliced surfaces further shows that laser-induced amorphous Si/C and lattice disorder accumulate mainly above the crack plane, leading to an asymmetry between the upper and lower halves of the specimen. These results establish a minimal N = 2 (double-pulse) MHz-burst configuration that enhances lateral-crack interconnection and lowers surface roughness.

My comments concern the important error in the structure analysis of the studied sample. The presented structural data do not correspond to (BiFeO₃)_0.80(MgTiO₃)_0.20, as supposed by authors. The numerical data are copied from BiFe_0.75Mn_0.25O₃ but the diffraction pattern is similar to BiMg_0.5Ti_0.5O₃ crystal.

This study investigates the microstructural evolution and corrosion behaviour of a CoCrFeMnNi high-entropy alloy (HEA) weld overlay applied to additively manufactured Inconel 718 (IN718) for high-temperature solar concentrator tube applications. Potentiodynamic polarization tests in 3 M NaCl solution revealed that the as-built AM IN718 exhibited a corrosion rate of 16.30 mils/year, indicating superior resistance in aqueous chloride media. In comparison, the HEA overlayed IN718 exhibited a more negative E_corr (- 0.633 V), higher I_corr (2.314X10⁻⁶ A), lower Rp (9920.8 Ω-cm²), and an elevated corrosion rate of 49.66 mils/year, relative to AM IN718 (-0.526 V, 6.827X10⁻⁷ A, 35,078.9 Ω-cm², and 16.30 mils/year, respectively). For high-temperature assessment, specimens were exposed to molten LiCl–KCl-EuCl₃ salt at 500 °C for 96 h. Under molten salt conditions, the HEA weld overlay significantly enhanced corrosion resistance as reflected by the reduced mass gain of 0.34 g/cm² compared to uncoated IN718, which recorded a mass gain of 0.95 g/cm². Microstructural characterization demonstrated pronounced grain refinement, formation of stable phases, and suppression of oxygen and chlorine ingress within the HEA-coated region. The overlay effectively mitigated salt-induced degradation and preserved substrate integrity. Hence, CoCrFeMnNi HEA weld overlay is a promising surface engineering approach to extend the service life of IN718 components in aggressive, high-temperature environments.

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Tungsten oxide (WO₃) thin films are being studied for a wide variety of sensing applications. This paper discusses structural, morphological, and optical characteristics of RF sputtered WO₃ films deposited on Si (100) substrates and subsequently annealed at 600 °C for 1 h in air. The films are named as T1 (450 nm thick), T2 (2000 nm thick), and T3 (3000 nm thick). All the annealed WO₃ films showed the presence of monoclinic and orthorhombic mixed phases. The WO₃ films exhibited multiple Raman peaks due to the W-W vibration modes (134 cm^− 1, 187 cm^− 1), O-W-O bending modes (274 cm^− 1, 326 cm^− 1), and W-O-W stretching modes (717 cm^− 1, 806 cm^− 1). Increased Raman peak intensities with the film thickness arise due to the improved crystalline quality. Optical band gaps of the films are found to be 3.4 eV (T1), 2.88 eV (T2), and 2.84 eV (T3). The variation of the band gaps seems to be due to the presence of different proportions of monoclinic and orthorhombic phases. The films showed coupling of IR-photons and surface phonons in the 800–980 cm^− 1 regions in the infrared (IR) attenuated total reflectance (IR-ATR) spectroscopy measurement. The WO₃ films exhibited the surface phonon polariton (SPP) absorption dip at 920 cm^− 1 (T1), 875 cm^− 1 (T2), and 897 cm^− 1 (T3). Corresponding broadening (full width half maxima) of the SPP dip are found to be 99 cm^− 1 (T1), 125 cm^− 1 (T2), and 57 cm^− 1 (T3). Improved texture coefficient (TC) corresponding to the (002) plane in the sample T3 (3.6) can be attributed to the underlying reason for sharper SPP absorption in the T3 sample compared to TC of the other two films (T1: 1.6, and T2: <1.0) as the Evanescent wave come out normally from the film surface during the IR-ATR spectroscopy measurement.

In this work, the effects of Ta₂O₅ incorporation on the structure and dielectric properties of BT–BNT ceramics were systematically investigated. Ta₂O₅ addition was found to reduce tetragonality and improve the temperature stability of the dielectric permittivity. At Ta₂O₅ contents of 3 and 3.5 mol%, the room-temperature relative permittivities were 1143 and 1074, respectively, with capacitance variation within ± 15% over − 55 to 200 °C, meeting the X9R specification. However, both compositions exhibited a pronounced increase in dielectric loss above 100 °C, limiting their practical applicability. By introducing 0.8 mol% MnO₂ into the Ta-optimized composition (x = 0.03), the room-temperature dielectric loss was reduced to 0.01, and the high-temperature loss remained below 0.01 over the 100–200 °C range. Detailed analyses indicate that the enhanced thermal stability is associated with reduced tetragonality, increased B-site disorder, and a diffuse tetragonal–cubic phase transition, which collectively modify the ferroelectric–relaxor behavior. In contrast, the suppression of high-temperature dielectric loss arises from changes in high-temperature conduction mechanisms induced by Mn modification. These findings provide a viable strategy for developing BT–BNT based X9R-type MLCCs with simultaneously improved thermal stability and low dielectric loss.

Columbite-tantalite (Coltan) samples from Venezuela have been studied by the new procedures of Vacuum Deposition Laser Ablation (VD-LA), Liquid-Phase Laser Ablation (LP-LA), and by direct irradiation of finely pulverized material deposited as a liquid suspension coupled with Total Reflection X-Ray Fluorescence (TXRF). With VD-LA, the beam from pulsed third harmonic Nd:YAG laser pulses impinges directly on the face of the mineral sample in vacuum, depositing the ablated material on TXRF sample carriers. With LP-LA, mineral specimens were placed under distilled de-ionized water in a quartz cell and subjected to pulsed laser ablation. The nanoparticle suspension produced was analyzed by TXRF. Products were studied by Scanning Electron Microscopy, showing that liquid-phase ablated material forms spherical nanoparticles, with the composition close to the bulk concentration of the ablated products. The results of contained radioactivity, as well as the TXRF analysis, show the existence of significant variability in the composition of mineral specimens obtained from the Aguamena area in Venezuela.

This paper unveils the theoretical probing, microcontroller realization, and image encryption of a quadratically damped Josephson junction (JJ) circuit with 4π-periodic superconducting current (QDJJC4PSC). The differential equation representing the model is established based on the fundamental Kirchhoff’s laws and steady state analysis results in two steady states: the stable and saddle nodes, distinguished by the Routh-Hurwitz criteria. Numerical simulations demonstrate a range of dynamic behaviours, including bursting oscillations, periodic, chaotic, coexisting, hidden, periodic bubbles and chaotic bubbles attractors, and antimonotonicity phenomenon. The experimental validation of the simulated results using microcontroller implementation shows qualitative agreement. Offset boosting control unveils the perfect transition of complex signals in the voltage and current state QDJJC4PSC variables. The NIST-800.22 tests validate the ability of the chaotic attractor uncovered in the QDJJC4PSC to be used for generating random numbers. The key generation, the steps of the proposed encryption and decryption algorithms based on zigzag permutation and XOR diffusion are presented, as well as the results of the various analyses conducted to evaluate the security and robustness of the proposed encryption scheme. The chaotic characteristic uncovered in the QDJJC4PSC has successfully demonstrated its use for medical images encryption applications based on zigzag permutation and XOR diffusion. The results underscore the practical impact and methodological rigor of our findings.

The magnetocaloric effects of the La_0.52Y_0.15Ca_0.33MnO_3-δ compound is reported to cover an extensive temperature range, approaching room-temperature and lower temperatures, making it a viable candidate for magnetic refrigeration. Moreover, the relative cooling power of the La_0.52Y_0.15Ca_0.33MnO_3-δ compound reaches 454 J/Kg, surpassing the levels of popular magnetic refrigerants like (La–Sr)MnO₃, J/Kg, (La–Sr)MnO₃, (La–Ca–Pb)MnO₃, and for Gd, and La_1-xCa_xMnO₃ compounds. The La_0.52Y_0.15Ca_0.33MnO_3-δ compound can function as an individual magnetic refrigerant in MR at temperatures close to room temperature and below ones. La_0.52Y_0.15Ca_0.33MnO_3-δ compound is a promising magnetic refrigerant for different purposes.