Applied Physics A最新文献

The present study aimed to understand the structural, magnetic, and electrical features of MFe₂O₄ nanocrystals (M = Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺) synthesized via simple co-precipitation route and doing a comparative study with materials prepared using other routes. XRD showed the single-phase cubic structure formation for the samples only after calcination at 700^oC. An exception was obtained with MgFe₂O_4, which retains the Fe₂O₃ secondary phase, and CuFe₂O_4, which showed a structure transformation into a tetragonal phase. FT-IR spectroscopy indicated the pronouncing of the atomic weight effect on the ionic radii when discussing the present difference in the bands` positions. Agglomerated sphere-like cluster morphologies were detected through a TEM study. Magnetic studies showed ferromagnetic properties for CoFe₂O₄ and CuFe₂O₄, as well as superparamagnetic properties for the other ferrites. Also, only CoFe₂O₄ and CuFe₂O₄ showed hard ferrite types, while others indicated soft ones. The electrical investigations exhibited semi-conducting properties for all the samples, accompanied by a transition in the conduction mechanism from hopping to polaron as the temperature rose. The obtained conductivities order is CuFe₂O₄ > CoFe₂O₄ > ZnFe₂O₄ > NiFe₂O₄ > MgFe₂O₄. The low dielectric values obtained suggest the use of entire ferrites in microwave applications.

Carbon nitride is a good inorganic non-metallic material, and is widely used in the photocatalysis. However, its photocatalytic performance is significantly related to its morphological characteristics, especially its nanosheet-like morphology has recently attracted keen interest. In this paper, a soluble salt-assisted route is adopted. By ball milling melamine and Na₂SO₄ powder, the precursor can be evenly distributed over the surface of Na₂SO₄ particulates. Then through the thermal decomposition reaction, and finally by washing Na₂SO₄ with water, a large amount of carbon nitride nanosheet powders can be obtained. After the examinations by XRD, SEM, XPS, PL, and BET, the results show that the product has a hexagonal phase C₃N₄ structure, sheet-like morphology with two-dimensional sizes of several micrometers and a thickness of ten nanometers, a large surface area of 23.89 m²/g and a low PL intensity centered at 450 nm when compared with the bulk C₃N₄ powders, well known for enhancing its photocatalytic efficiency. According to expectation, the dye photocatalytic degradation rate over the C₃N₄ nanosheets is 90% in 30 min, but only 60% in the same time on bulk C₃N₄. Moreover the photocatalytic degradation reactions follow pseudo-first-order reaction kinetics, and the former rate constant is more than twice that the latter.

Graphical abstract

By ball milling melamine and sodium sulfate powder, the precursor can be evenly distributed over Na₂SO₄. Then through the thermal decomposition reaction, and finally by washing sodium sulfate with water, the pure carbon nitride nanosheets can be obtained

MBene, as a subset of the innovative two-dimensional material MXene, has attracted considerable research attention in recent years. The present study uses Monte Carlo simulation to investigate the magnetic behaviors, thermodynamic characteristics, and magnetocaloric effect of MnB. Our results indicate that reducing the exchange couplings and absolute magnitudes of the crystal field, or conversely, increasing the external magnetic field, can enhance the maximum values of the isothermal magnetic entropy change. In addition, the effects of the crystal field, exchange couplings and external magnetic field on the relative cooling power are investigated.

Based on the distinctive characteristics of Layered Double Hydroxides (LDHs), extensive research has focused on their sensory properties and their application as electrochemical and gas sensors using various methods such as cataluminescence (CTL) and resistance measurements. In this study, we have rigorously examined the sensing capabilities of the Ni-Cr LDH sensor in the presence of acetone and ethanol at room temperature. Subsequently, we have compared these results with the sensing properties of the Ni-Cr-Al LDH and Ni-Cr LDH/TiO₂ sensors under identical conditions, leading to a comprehensive discussion on the impact of Al³⁺ and titanium oxide on the sensors’ sensing properties. The Ni-Cr LDH/TiO₂ sensor showed better sensitivity to acetone and ethanol than the other two sensors. Besides, the Ni-Cr LDH/TiO₂ sensor exhibited shorter recovery and response times in the presence of acetone. Conversely, the Ni-Cr LDH sensor had quicker recovery and response times in the presence of ethanol, outperforming the other sensors.

A three-dimensional transient finite element model of laser cladding 316 L stainless steel was established to study the evolution of temperature and stress fields under different process parameters. The effects of process parameters on the surface morphology, hardness distribution and wear resistance of 316 L stainless steel cladding layer were investigated, and the wear mechanism was analyzed. The simulation results indicate that the nodal temperature trends during laser cladding are similar across different process parameters, with temperatures rising to a peak and then gradually cooling to room temperature as the heat source moves through. Residual stresses are primarily located on both sides of the bond between the cladding and the substrate, with the highest stresses in the laser scanning direction. Excessive or insufficient laser power and scanning speed result in poor surface quality of the cladding. The hardness of the cladding layer is negatively correlated with laser power and positively correlated with scanning speed, showing a gradual increase from the substrate-cladding interface to the top of the cladding. The friction coefficient of the cladding increases with laser power and decreases with scanning speed. The main wear mechanisms of the cladding coating are abrasive, adhesive, and oxidative wear.

In the present work, the effect of adding Ba_0.4Sr_0.4Ca_0.2Fe₁₂O₁₉ hard nanoparticles and the immersion in seawater for different durations (0, 2, 6, 12, and 24 h) on the mechanical characteristics of the Bi, Pb-2223 superconductor phase were studied. A conventional solid-state reaction method was used to produce the (Ba_0.4Sr_0.4Ca_0.2Fe₁₂O₁₉)_x/(Bi_1.6, Pb_0.4)-2223 composites (0.00 ≤ x < 0.40 wt%). X-ray diffraction (XRD) confirmed the primary phase formation of the tetragonal (Bi_1.6, Pb_0.4)-2223. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) studies were also carried out to demonstrate the microstructural analyses of the samples during seawater immersion. Compared to the pure (Bi_1.6, Pb_0.4)-2223 phase, SEM and EDX verified the improvement of the adsorption of seawater elements upon adding the nanoparticles. This resulted in faster grain size reduction in the (Bi_1.6, Pb_0.4)-2223 phase than in the pure sample before immersion. Vickers microhardness ((:Hv)) Measurements were performed for 30 s at room temperature, with applied stresses ranging from 0.49 to 9.80 N after immersion in the seawater for different durations (0, 2, 6, 12, and 24 h). For the sample with x = 0.04 wt%, (:Hv) values enhanced with percentages of 67.72% and 98.44%, before and after immersion in seawater for 24 h, respectively. This suggests that the mechanical properties of the (Bi_1.6, Pb_0.4)-2223 phase were enhanced by a small addition of these nanoparticles and the salts of seawater adsorbed on the sample’s surface. The modified proportional sample resistance (MPSR) model offered the most accurate theoretical analysis in the plateau limit region, before and after seawater immersions, with a less than 5% variance. Furthermore, the incorporation of Ba_0.4Sr_0.4Ca_0.2Fe₁₂O₁₉ into the superconductor had a positive impact on several mechanical characteristics, including fracture toughness (K), yield strength (Y), and elastic modulus (E). All these mechanical parameter values followed the same trend, increasing with the increase in immersion time. However, they are at their height with the presence of 0.04 wt% of these nanoparticles. The toughness increased by 27.31% of the pure sample at this point. After that, when the immersion time rose from 0 to 24 h, this number increased by 42.59%.

High entropy alloys (HEAs) are multi-component metallic materials renowned for their exceptional thermal stability, superior corrosion resistance, and other outstanding properties, which make them highly promising for various applications. This study investigates the tensile mechanical characteristics of the Al_0.3CoCr_xFeNi high entropy alloys with varying chromium (Cr) contents (at%) through Molecular Dynamics simulations (MD). The results indicate that the tensile strength and elongation exhibit similar fluctuations. The mechanism of plastic deformation in the alloy transitions from a combined process involving both dislocation slip and twin deformation to one that is primarily characterized by single twin deformation. This change can be attributed to the lattice distortion induced by the incorporation of Cr into the alloy. Furthermore, a thorough investigation was conducted to assess the influence of temperature and strain rates on the mechanical properties of these alloys. Temperature fluctuations significantly affect the mechanical characteristics of the Al_0.3CoCr_xFeNi high-entropy alloys. As the temperature increases, the Young’s modulus, tensile strength, and toughness decrease. Under the conditions of low strain rates and gradually rising temperature, the tensile strength, Young’s modulus, and elongation of the Al_0.3CoCr_1.0FeNi HEAs decreased by 4.55 GPa, 12.91 GPa, and 2.9%, respectively. The plastic deformation mechanism gradually shifts from predominantly twin deformation to the coexistence of twin and dislocation slip. The tensile strength and elongation rise with an increase in strain rate. This phenomenon is attributed to the high stress levels at elevated strain rates, which activate multiple dislocation sources simultaneously, thereby increasing the number of dislocations and their interactions, leading to enhanced strength.

The polycrystalline double perovskite La₂NiFeO₆ nanocrystallites were synthesized using the wet chemical sol–gel method. X-ray diffraction (XRD) analysis confirmed the formation of a single-phase material with a monoclinic P_21/n structure and an estimated crystallite size of 17 nm. Selected Area Electron Diffraction (SAED) patterns revealed the presence of diffraction rings, further indicating the monoclinic structure. Dielectric and impedance studies, conducted as functions of temperature and frequency, highlighted the contributions of grains and grain boundaries to the relaxation processes. The AC conductivity values ranged from 2.45 × 10^–5 S/m to 5.51 × 10^–5 S/m S/m over a temperature range of 300 K to 473 K at a frequency of 2 kHz. Notably, La₂NiFeO₆ exhibits novel ferromagnetic semiconductor properties and undergoes a spin glass transition at approximately 50 K. This comprehensive investigation provides the first report on the structural, dielectric, and magnetic properties of La₂NiFeO₆, underscoring its potential as a promising material for advanced data storage and spintronic device applications.

Carbon nanoparticles (CNPs) with unique photoluminescence properties have promising potential for detecting volatile organic compounds. In this work, employing folic acid as the carbon source and citric acid as the surface modifier, blue fluorescent CNPs were synthesized using a simple and inexpensive hydrothermal method. These CNPs feature an amorphous carbon structure and present a reduced size of 24 nm and an increased presence of carbonyl groups on their surface owing to the incorporation of citric acid, demonstrating enhanced surface defect states and exhibiting excitation-dependent fluorescence behavior. The citric acid-assisted composite CNPs exhibit excellent optical selectivity towards triethylamine (TEA), with a particularly optical response, enhancing at low concentrations and quenching at high concentrations. The synergistic effect of electron transfer results in high sensitivity and a low detection limit of 0.28 µM. The synthesized CNPs serve as fluorescent probes for TEA in an aqueous medium. The detection mechanism of citric acid-assisted CNPs is explored in detail.