Search Results (20)

Hydrogels represent a versatile class of materials with remarkable potential as three-dimensional matrices for nanoparticle integration. This study explores the mechanism of silver nanoparticle formation within a polyacrylamide–alginate hybrid hydrogel, employing a controlled reduction–oxidation reaction between silver nitrate (AgNO₃) and sodium borohydride (NaBH₄) across a temperature gradient (5–70 °C). Characterization techniques, including Raman, infrared, and UV-Vis spectroscopies, X-ray diffraction, and scanning electron microscopy, were employed to analyze the structural and optical properties of the nanoparticles and the hydrogel. The results show that, as the temperature rose, nanoparticle numbers decreased, while their size increased. Consistently octahedral in shape and averaging 100–120 nm, these nanoparticles revealed a temperature-dependent growth pattern, with rare larger crystals emerging more frequently at higher temperatures. The findings highlight the potential of hybrid hydrogels as effective matrices for the incorporation of metal nanoparticles, paving the way for applications in drug delivery, biosensing, and antimicrobial treatments. Full article

Double perovskite materials have emerged as key players in the realm of advanced materials due to their unique structural and functional properties. This research mainly focuses on the synthesis and comprehensive characterization of Ba₂CoWO₆ double perovskite nanopowders utilizing a high-temperature conventional solid-state reaction technique. The successful formation of Ba₂CoWO₆ powders was confirmed through detailed analysis employing advanced characterization techniques. Rietveld refinement of X-ray diffraction (XRD) and Raman data established that Ba₂CoWO₆ crystallizes in a cubic crystal structure with the space group Fm-3m, indicative of a highly ordered perovskite lattice. The typical crystallite size, approximately 65 nm, highlights the nanocrystalline nature of the material. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) discovered a distinctive morphology characterized by spherical shaped particles, suggesting a complex particle formation process influenced by synthesis conditions. To probe the electronic structure, X-ray Photoelectron Spectroscopy (XPS) identified cobalt and tungsten valence states, critical for understanding dielectric properties associated with localized charge carriers. The semiconducting character of the synthesized Ba₂CoWO₆ nanocrystalline material was confirmed through UV-Visible analysis, which revealed an energy bandgap value of 3.3 eV, which aligns well with the theoretical predictions, indicating the accuracy and reliability of the experimental results. The photoluminescence spectrum exhibited two distinct emissions in the blue-green region. These emissions were attributed to the transitions ³P₀→³H₄, ³P₀→³H₅, and ³P₀→³H₆, primarily resulting from the contributions of Ba²⁺ ions. The dielectric characteristics of the compound were analyzed across a different range of frequencies, spanning from 1 kHz to 1 MHz. Magnetic characterization using Vibrating Sample Magnetometry (VSM) revealed antiferromagnetic behavior of Ba₂CoWO₆ ceramics at room temperature, attributed to super-exchange interactions between Co³⁺ and W⁵⁺ ions mediated by oxygen ions in the perovskite lattice. Additionally, first-principles calculations based on the Generalized Gradient Approximation (GGA+U) with a modified Becke–Johnson (mBJ) potential were employed to gain a deeper understanding of the structural and electronic properties of the materials. This approach involved systematically varying the Hubbard U parameter to optimize the description of electron correlation effects. These results deliver an extensive understanding of the structural, optical, morphological, electronic, and magnetic properties of Ba₂CoWO₆ ceramics, underscoring their potential for electronic and magnetic device applications. Full article

Laser ablation was used to successfully fabricate multiferroic bilayer thin films, composed of BaTiO₃ (BTO) and CoFe₂O₄ (CFO), on highly doped (100) Si substrates. This study investigates the influence of BaTiO₃ layer thickness (50–220 nm) on the films’ structural, magnetic, and dielectric properties. The dense, polycrystalline films exhibited a tetragonal BaTiO₃ phase and a cubic spinel CoFe₂O₄ layer. Structural analysis revealed compression of the CoFe₂O₄ unit cell along the growth direction, while the BaTiO₃ layer showed a tetragonal distortion, more pronounced in thinner BTO layers. These strain effects, attributed to the mechanical interaction between both layers, induced strain-dependent wasp-waisted behavior in the films’ magnetic hysteresis cycles. The strain effects gradually relaxed with increasing BaTiO₃ thickness. Raman spectroscopy and second harmonic generation studies confirmed BTO’s non-centrosymmetric ferroelectric structure at room temperature. The displayed dielectric permittivity dispersion was modeled using the Havriliak–Negami function combined with a conductivity term. This analysis yielded relaxation times, DC conductivities, and activation energies. The observed BTO relaxation time behavior, indicative of small-polaron transport, changed significantly at the BTO ferroelectric Curie temperature (Tc), presenting activation energies E_τ in the 0.1–0.3 eV range for T < Tc and E_τ > 0.3 eV for T > Tc. The BTO thickness-dependent Tc behavior exhibited critical exponents ν ~ 0.82 consistent with the 3D random Ising universality class, suggesting local disorder and inhomogeneities in the films. This was attributed to the composite structure of BTO grains, comprising an inner bulk-like structure, a gradient strained layer, and a disordered surface layer. DC conductivity analysis indicated that CoFe₂O₄ conduction primarily occurred through hopping in octahedral sites. These findings provide crucial insights into the dynamic dielectric behavior of multiferroic bilayer thin films at the nanoscale, enhancing their potential for application in emerging Si electronics-compatible magneto-electric technologies. Full article

Stabilized Li_6.25La₃Al_0.25 Zr₂O₁₂ (cubic LLZO or c-LLZO) is a Li⁺-conducting ceramic with ionic conductivities approaching 1 mS-cm. Processing c-LLZO so that it is suitable for use as a solid state electrolyte in all solid state batteries, however, is challenging due to the formation of secondary phases at elevated temperatures. The work described in this manuscript examines the formation of one such secondary phase La₂Zr₂O₇ (LZO) formed during sintering c-LLZO at 1000 °C. Specifically, spatially resolved Raman spectroscopy and X-ray Diffraction (XRD) measurements have identified gradients in Li distributions in the Li ion (Li⁺)-conducting ceramic Li_6.25La₃Al_0.25 Zr₂O₁₂ (cubic LLZO or c-LLZO) created by thermal processing. Sintering c-LLZO under conditions relevant to solid state Li⁺ electrolyte fabrication conditions lead to Li⁺ loss and the formation of new phases. Specifically, sintering for 1 h at 1000 °C leads to Li⁺ depletion and the formation of the pyrochlore lanthanum zirconate (La₂Zr₂O₇ or LZO), a material known to be both electronically and ionically insulating. Circular c-LLZO samples are covered on the top and bottom surfaces, exposing only the 1.6 mm-thick sample perimeter to the furnace’s ambient air. Sintered samples show a radially symmetric LZO gradient, with more LZO at the center of the pellet and considerably less LZO at the edges. This profile implies that Li⁺ diffusion through the material is faster than Li⁺ loss through volatilization, and that Li⁺ migration from the center of the sample to the edges is not completely reversible. These conditions lead to a net depletion of Li⁺ at the sample center. Findings presented in this work suggest new strategies for LLZO processing that will minimize Li⁺ loss during sintering, leading to a more homogeneous material with more reproducible electrochemical behavior. Full article

Tetra-n-butylammonium Bromide (TBAB) finds extensive use in diverse applications. An in-depth investigation into the effects of the formation conditions on TBAB hydrate is necessary to optimize the application process. This work focuses on examining the influence of the mass concentration of TBAB solution and the cooling rate on TBAB hydrate formation through optical microscopy and Raman spectroscopy. The TBAB hydrate formation process occurs in a confined space created by an optical sheet with a 0.03 mm deep groove. Four TBAB solutions of 13. 8 wt%, 18 wt%, 32 wt%, and 40 wt% are investigated, and the supercooling required for hydrate nucleation increases with concentration at a cooling rate of 0.5 K/min. Notably, Type A TBAB hydrate preferentially forms in all of the solutions, although type B hydrate is thermodynamically stable in the two dilute solutions. At a larger cooling rate of 2 K/min, two distinct crystal growth patterns are observed: one controlled by mass transfer and the other regulated by heat transfer. Increasing the cooling rate not only alters the optical morphology, but also reduces the supercooling due to a decrease in the Gibbs free energy barrier caused by a larger temperature gradient. This is beneficial for practical applications as it helps to alleviate the supercooling degree. Full article

Mineral dehydration in the subduction zone enormously affects Earth’s geodynamics and the global geochemical cycles of elements. This work uses Raman spectroscopy and X-ray diffraction to investigate the dehydration process of antigorite under compression and shear loading conditions in a rotational diamond anvil cell (RDAC) at room temperature. In order to compare the shear effects, T301 stainless steel and Kapton plastic are applied as the gasket materials. In the experiment using a high-strength T301 stainless steel gasket, two new broad OH-stretching peaks of H₂O and H₃O₂⁻ appear at 3303 and 3558 cm⁻¹, respectively, at 1.7 GPa. The original sharp OH-stretching peaks of antigorite at 3668 and 3699 cm⁻¹ remain, while the central pressure is increased to 8.0 GPa, and the largest pressure gradient is about 2.5 GPa in the sample chamber. In another experiment with a low-strength gasket of Kapton plastic, two new OH-stretching broad peaks of H₂O and H₃O₂⁻ also start to appear at 3303 and 3558 cm⁻¹, respectively, at a lower pressure of 0.3 GPa, but the original sharp OH-stretching peaks of antigorite at 3668 and 3699 cm⁻¹ almost completely vanish as the central pressure reaches 3.0 GPa, with the largest pressure gradient at around 4.8 GPa. The comparison between the two experiments shows that antigorite is easier to dehydrate in the chamber of a Kapton plastic gasket with a larger gradient of shear stress. However, its axial compression stress is lower. The high-pressure Raman spectra of MgO₂(OH)₄ octahedron and SiO₄ tetrahedron in the low wavenumber zones (100–1200 cm⁻¹) combined with the micro-beam X-ray diffraction spectrum of the recovered product strongly support the structural breakdown of antigorite. This investigation reveals that the water-bearing silicate minerals have strong shear dehydration in the cold subduction zone of the plate, which has important applications in predicting the physical and chemical properties of subduction zones and deducing the rate of plate subduction. Full article

The glass crystallization regime plays a crucial role in the fabrication of glass ceramics: it affects both phase composition and microstructure, and thus the properties of the final product. In the search for new glass-ceramic materials, the development of a proper heat-treatment schedule involves the utilization of numerous glass samples that need to be thermally treated and then investigated to determine the values of the target characteristics. In this study, we evaluated the effect of crystallization temperature on the glass structure, phase composition, and hardness of glass ceramics in the ZnO-MgO-Al₂O₃-SiO₂ system containing TiO₂ and ZrO₂ as nucleators. To maximize the number of heat treatments, we performed polythermal crystallization of the glass in a wide temperature range with the help of a gradient furnace. Using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy, we showed the precipitation of gahnite nanocrystals as the main phase in the bulk of a single glass sample and observed a gradual change in its microstructure, transparency, and hardness. The dependence of Vickers hardness values on heat treatment temperature was found to follow a non-linear trend, revealing the optimal thermal range for glass crystallization. Full article

Near-infrared spectrophotometry and partial least squares regression (PLSR) were evaluated to create a pleasantly simple yet effective approach for measuring HNO₃ concentration with varying temperature levels. A training set, which covered HNO₃ concentrations (0.1–8 M) and temperature (10–40 °C), was selected using a D-optimal design to minimize the number of samples required in the calibration set for PLSR analysis. The top D-optimal-selected PLSR models had root mean squared error of prediction values of 1.4% for HNO₃ and 4.0% for temperature. The PLSR models built from spectra collected on static samples were validated against flow tests including HNO₃ concentration and temperature gradients to test abnormal conditions (e.g., bubbles) and the model performance between sample points in the factor space. Based on cross-validation and prediction modeling statistics, the designed near-infrared absorption approach can provide remote, quantitative analysis of HNO₃ concentration and temperature for production-oriented applications in facilities where laser safety challenges would inhibit the implementation of other optical techniques (e.g., Raman spectroscopy) and in which space, time, and/or resources are constrained. The experimental design approach effectively minimized the number of samples in the training set and maintained or improved PLSR model performance, which makes the described chemometric approach more amenable to nuclear field applications. Full article

In this study, the structural evolution of the CdTe/ZnS composite passivation films on the surface of infrared HgCdTe material before and after annealing was comparatively explored. The surface morphology and microstructure of the passive films before and after annealing were characterized by scanning electron microscope, X-ray diffraction, atomic force microscopy, and Raman and X-ray photoelectron spectroscopy to determine the effects of the annealing process on the surface crystal defects of the films. The results show that annealing at 320 °C for three hours can improve crystal quality, ameliorate the surface density, and reduce the dislocation density of grains, while the Hg grains inhibited by tellurium-rich growth during the annealing process return to the normal growth state, and the S signal can be detected near the surface after annealing. This finding indicates that high-temperature annealing promotes the inhibited grain growth and also causes diffusion of surface elements, thus smoothing the compositional gradient at the passivation interface of the films. Full article

Contact metamorphism in coal is usually characterized by a rapid, brief, and exotherm reaction that can change the geothermal gradient. In this process, coal adjacent to the intrusive body can form thermally altered coal-based graphite (TACG). In order to further study the structural changes of TACG at different distances from the intrusive body, four TACG samples were collected in the Zhuji coal mine in the Huainan Coalfield, North China, and their vitrinite reflectance and Raman spectra were measured using polarizing microscopy and Raman spectroscopy. The results showed that: (1) affected by the temperature and stress of magmatic hydrothermal intrusion, the clay minerals in the coal seams appeared distributed in strips; the occurrence of ankerite and pyrite in the coal seams near the magmatic intrusions could be due to a late magmatic hydrothermal mineralization; (2) the R_max − R_min correlation for the TACG samples under study showed that thermal metamorphism was the main factor leading to the graphitization of the TACG samples, without an obvious pressure effect; (3) with the increase of the graphitization process, the D- and G-band showed some similar changes, specifically, their peak positions shifted to lower wave numbers, and the full width at half maximum (FW_G and FW_D) gradually decreased; the difference was that the intensity of the G-band increased, while that of the D-band decreased; (4) the graphitization degree of the TACG samples increased with the increase of the transverse size of the crystals, while the FW_G and FW_D values of the G- and D-band decreased; (5) in comparison to natural graphite, the TACG still presented structural defects. Full article

We synthesized a combinatorial library of Cu_xNi_1−x alloy thin films via co-sputtering from Cu and Ni targets to catalyze graphene chemical vapor deposition. The alloy morphology, composition, and microstructure were characterized via scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and X-ray diffraction (XRD), respectively. Subsequently, the Cu_xNi_1−x alloy thin films were used to grow graphene in a CH₄-Ar-H₂ ambient at atmospheric pressure. The underlying rationale is to adjust the Cu_xNi_1−x composition to control the graphene. Energy dispersive x-ray spectroscopy (EDS) analysis revealed that a continuous gradient of Cu_xNi_1−x (25 at. % < x < 83 at.%) was initially achieved across the 100 mm diameter substrate (~0.9%/mm composition gradient). The XRD spectra confirmed a solid solution was realized and the face-centered cubic lattice parameter varied from ~3.52 to 3.58 $\dot{\mathrm{A}}$, consistent with the measured composition gradient, assuming Vegard’s law. Optical microscopy and Raman analysis of the graphene layers suggest single layer growth occurs with x > 69 at.%, bilayer growth dominates from 48 at.% < x < 69 at.%, and multilayer (≥3) growth occurs for x < 48 at.%, where x is the Cu concentration. Finally, a large area of bi-layer graphene was grown via a Cu_xNi_1−x catalyst with optimized catalyst composition and growth temperature. Full article

Iron oxides/hydroxides are important magnetic minerals to provide information about changes in the forming environment. However, the magnetic behavior in agate has been rarely investigated. In this study, the magnetic behavior of the Xuanhua-type agate with intense yellow to red colors from the Xuanhua District (China) was investigated by temperature dependence of magnetic susceptibility, hysteresis loop, isothermal remanent magnetization and the analysis of remanent coercivity components from the gradient acquisition plot. Yellow goethite and red hematite can be quantitatively identified by XRD and Raman spectroscopy due to their relatively higher content. Results showed that the red, yellow and orange Xuanhua-type agate had different magnetic behavior, and magnetite existed in the yellow and orange ones. Fluid inclusions in such agate had the homogenization temperature of ~168 °C to 264 °C. All results suggested that the dehydration of goethite to form hematite was the main reason for the high remnant coercivity (above 1000 mT) of hematite in the red agate. The co-existence of magnetite and goethite in the yellow and orange agate reflects the transformation from Fe²⁺ to Fe³⁺, indicating the change in the redox property of the environment. Unique patterns mainly formed by hematite and goethite make it a popular gem-material with high research value. Full article

Single wall carbon nanotubes (SWCNTs) were grown on either sized or desized carbon fabric in a self-designed reactor by Pulsed Laser Deposition (PLD). The uniqueness of the PLD system lies, among other things, in the ability to keep the substrate at a low temperature, compared to the 1100 °C needed for the SWCNTs synthesis, thus, rendering it undamaged. Samples were placed at different positions on a cold finger (CF), where a temperature gradient develops, in the range 25–565 °C. The chemical composition and morphology of desized and surface treatments, as well as SWCNTs grown on carbon fibres, were verified by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDX), while the quality of SWCNTs was proven by confocal micro-Raman Spectroscopy and High-Resolution Scanning Transmission Electron Microscopy (HR-STEM). Fibres covered with SWCNTs by PLD were characterized using contact angle and the surface free energy was calculated. A micro-droplet pull-out test was used to evaluate the effect of SWCNTs over interfacial properties of a carbon-epoxy composite. A 20% increase in interfacial shear strength (IFSS) was observed by deposition at 290 °C, compared to the commercial carbon fibre sizing. The carbon fibres kept their tensile properties due to the low deposition temperatures. Full article

A nanostructured hybrid material consisting of TiO₂ nanoparticles grown and stabilized on graphene oxide (GO) platelets, was synthesized and tested as nanofiller in a polymeric matrix of sulfonated polysulfone (sPSU) for the preparation of new and low-cost nanocomposite electrolytes for proton exchange membrane fuel cell (PEMFC) applications. GO-TiO₂ hybrid material combines the nanoscale structure, large interfacial area, and mechanical features of a 2D, layered material, and the hygroscopicity properties of ceramic oxides, able to maintain a suitable hydration of the membrane under harsh fuel cell operative conditions. GO-TiO₂ was synthetized through a new, simple, one-pot hydrothermal procedure, while nanocomposite membranes were prepared by casting using different filler loadings. Both material and membranes were investigated by a combination of XRD, Raman, FTIR, thermo-mechanical analysis (TGA and Dynamic Mechanical Analysis) and SEM microscopy, while extensive studies on the proton transport properties were carried out by Electrochemical Impedance Spectroscopy (EIS) measurements and pulse field gradient (PFG) NMR spectroscopy. The addition of GO-TiO₂ to the sPSU produced a highly stable network, with an increasing of the storage modulus three-fold higher than the filler-free sPSU membrane. Moreover, the composite membrane with 3 wt.% of filler content demonstrated very high water-retention capacity at high temperatures as well as a remarkable proton mobility, especially in very low relative humidity conditions, marking a step ahead of the state of the art in PEMs. This suggests that an architecture between polymer and filler was created with interconnected routes for an efficient proton transport. Full article

Poly(amidoamine) (PAMAM)-based electrolytes are prepared by dissolving the PAMAM half-generations G1.5 or G2.5 in propylene carbonate (PC), either with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) or sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) salts. The solutions, designed for ion battery applications, are studied in terms of ions transport properties. Raman Spectroscopy reveals information about the interactions between cations and PAMAM dendrimers as well as full dissociation of the salts in all solutions. Pulsed-field gradient Nuclear Magnetic Resonance (PFG NMR), measured as a function of both temperature and PAMAM concentration, are obtained for the cation, anion, solvent, and dendrimer molecules using lithium (⁷Li), sodium (²³Na), fluorine (¹⁹F), and hydrogen (¹H) NMR, respectively. It was found that lithium diffusion is slow compared to the larger TFSI anion and decreases with PAMAM concentration due to interactions between cation and dendrimer. Comparison of conductivities calculated from diffusion coefficients using the Nernst–Einstein equation, with conductivity measurements obtained from Impedance Spectroscopy (IS), shows slightly higher IS conductivities, caused among others by PAMAM conductivity. Full article