Search Results (704)

Four liquid crystalline racemates, with oligomethylene spacer lengths of three and five and terminal alkyl chain carbon numbers of six and seven (acronyms 3PhPhC6, 5PhPhC6, 3PhPhC7, and 5PhPhC7), were synthesized. Racemates were characterized by their mesomorphic and thermodynamic properties. Identification of the liquid crystalline phases was performed using polarizing optical microscopy (POM), and the temperatures and enthalpies of phase transitions were determined by differential scanning calorimetry (DSC). Two selected racemates were used as dopants in antiferroelectric mixtures with investigated properties, and the effects of their addition on the mesomorphic properties of these mixtures were examined. The helical pitch of the doped mixtures was also measured using UV-Vis spectrophotometry. Racemates containing six carbon atoms in the alkyl chain (C6) exhibit the following phase sequence of Cr-SmC_A-SmC-SmA-Iso, while racemates with seven carbon atoms (C7) exhibit the following phase sequence of Cr-SmC-SmA-Iso. Racemate-doped mixtures exhibit a very wide range of the antiferroelectric phase and slightly higher clearing points than the base mixtures. The helical pitch of the racemate-doped mixtures is longer than that of the base mixtures. Racemates containing seven carbon atoms in the alkyl chain have the potential to be used in the ferroelectric mixtures due to the absence of an anticlinic phase. Full article

Removing mercury (Hg²⁺) from aqueous environments remains a major environmental challenge due to its high toxicity and bioaccumulation. Graphene quantum dots (GQDs) are adsorbents that show promise in removing these contaminants, but their yield is low in their pristine form. This study investigates the effect of phosphorus (P) doping on vacancy-containing GQDs to enhance Hg²⁺ absorption using density functional theory (DFT) calculations. These were performed at the M06-2X/def2-TZVP level of theory to optimize the structures of GQDs, 1P-GQDs, and 2P-GQDs to evaluate adsorption energies, frontier molecular orbitals, and dipole moments. The results show that GQDs with vacancy have an adsorption energy of −65.21 kcal mol⁻¹, which increases to −104.54 kcal mol⁻¹ for 1P-GQDs, indicating the strongest Hg²⁺ binding. However, 2P-GQD shows a lower value of −73.47 kcal mol⁻¹, suggesting lower efficiency due to electronic competition between dopants. Dipole moments increase from 0.8192 D (GQD) to 4.6729 D (1P-GQD) and 5.7557 D (2P-GQD), confirming strong polarization induced by P incorporation. The HOMO-LUMO gap decreases from 2.204 eV to 1.937 eV after single doping. At the same time, after Hg²⁺ adsorption, the values increase to 5.153 eV (GQD), 3.462 eV (1P-GQD), and 2.068 eV (2P-GQD), indicating configuration-dependent electronic stabilization. PDOS analysis confirms weak cation-π interaction in GQD and strong orbital hybridization in 1P-GQD, consistent with a coordination-type bond. Doping a single phosphate atom optimizes the electronic structure of GQDs with a vacancy site, thereby improving charge transfer and adsorption strength through electronic balance. Full article

With the advancement of electronics and communication technologies, there is growing interest in high-performance microwave-absorbing materials. The material composition and structural design are critical factors influencing the electromagnetic wave (EMW) absorption capabilities. X-type barium ferrite (Ba₂Co₂Fe₂₈O₄₆) exhibits advantages in enhancing high-frequency magnetic loss and interface polarization through its unique hexagonal crystal structure and morphological design, while also optimizing impedance matching to a certain extent. However, the effective absorption bandwidth (EAB) of single-phase barium ferrite is often restricted. Therefore, doping with other elements is necessary to broaden the EAB. In this study, La³⁺-substituted X-type hexagonal ferrites Ba₂Co₂Fe_28−xLa_xO₄₆ (x = 0.00, 0.05, 0.10, 0.15, and 0.20) were successfully synthesized via a high-temperature solid-state reaction method, and the effects of different La³⁺ doping concentrations on the electromagnetic parameters and wave-absorbing performance of Ba₂Co₂Fe₂₈O₄₆ were investigated. After doping, the materials demonstrated excellent electromagnetic absorption performance: when x = 0.15, RL_min = −48.36 dB; when x = 0.10, EAB = 9.03 GHz (RL ≤ −5 dB). Full article

In this study, we report the results of the structural characterization and electrochemical evaluation of novel cobalt-free layered Ruddlesden–Popper (RP) oxides, La₂SrFe₂O_7−δ and La₂SrFe_1.8Ga_0.2O_7−δ, as electrode materials for intermediate-temperature solid oxide cells. X-ray diffraction confirmed the formation of RP phases and phase stability after reducing treatment. The materials showed compatible thermal expansion behavior, with slightly lower thermal expansion coefficients for the Ga-doped composition. Oxygen pressure relaxation measurements demonstrated that the oxygen surface exchange coefficient increases with temperature and pO₂, while Ga substitution slightly reduces the O₂/oxide exchange rate, which may be associated with a lower concentration of oxygen vacancies. The electrical conductivity in air was higher for La₂SrFe₂O_7−δ than for the Ga-doped sample, while both compositions showed much lower conductivity under reducing conditions. Symmetrical cell impedance spectroscopy showed high polarization resistance for the electrodes, which was substantially reduced by applying a Ag current collector (0.43 Ω cm² for La₂SrFe₂O_7−δ and 0.73 Ω cm² for La₂SrFe_1.8Ga_0.2O_7−δ at 800 °C), consistent with the limited electronic conductivity of the oxide layers. Overall, both oxides exhibit structural stability, acceptable thermomechanical compatibility, and measurable oxygen exchange activity, making them promising candidates for further development as cobalt-free electrodes in solid oxide cells. Full article

Single-molecular white circularly polarized luminescence emitters show promise for use in chiral displays and solid-state lighting, but their design remains challenging because broadband emission, exciton utilization, color balance, and chiroptical activity must be integrated within one molecule. Herein, we report a chiral single-molecular white emitter, DCz-PTZ, constructed through a π-interrupted strategy by combining a rigid spiro framework, an oxygen-bridged carbazole/cyanobenzene segment, and a phenothiazine donor. The interrupted conjugation suppresses excessive charge-transfer (CT) domination and enables dual emissive channels, including short-wavelength locally excited (LE) emission and long-wavelength CT emission. DCz-PTZ exhibits near-ideal white emission in dilute toluene solution with CIE coordinates of (0.33, 0.33), and maintains balanced dual emission in 5 wt% doped films with CIE coordinates of (0.32, 0.34). Photophysical studies support the assignment of the yellow emission to a thermally activated delayed fluorescence (TADF)-active CT state. The enantiomers show mirror-image circularly polarized signals with |g_lum| up to 2.9 × 10⁻³. Optimized white organic light-emitting diodes (WOLEDs) achieve color rendering index (CRI) up to 92 and a maximum external quantum efficiency (EQE_max) of 1.3%. This work demonstrates a π-interrupted molecular strategy for integrating dual emission, TADF exciton utilization, and circularly polarized electroluminescence (CPEL) in a single chiral emitter. Full article

High-entropy alloy (HEA) coatings exhibit enhanced chemical stability when doped with carbon, primarily due to the strong bonding between carbon and transition metals. Typical transition metals used in these coatings include Cr, Fe, Co, Ni, Cu, Ti, V, W, Nb, Ta, and Zr. Owing to their excellent chemical stability, HEA coatings are widely employed to protect component surfaces operating in highly corrosive environments. Against this backdrop, the present study investigates the effect of carbon doping introduced via methane gas flow during the physical vapor deposition of TiAlTaZrNb HEA coatings on corrosion resistance. The morphology and structure of the coatings were analyzed by field emission scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. Corrosion protection and coating resistance were assessed through potentiodynamic polarization and electrochemical impedance spectroscopy. While increasing the methane flow resulted in an approximately 34% reduction in coating thickness, the overall coating resistance increased by one order of magnitude, reaching a maximum at a methane flow rate of 9 sccm, corresponding to the carbon solubility limit. This improvement was evidenced by a decrease in the corrosion rate from 8.02 × 10⁻² mm y⁻¹ for the uncoated H13 steel to 8.00 × 10⁻⁴ mm y⁻¹ for the HEA-coated samples. However, at higher methane flow rates, carbon precipitation and the formation of parallel microcracks contributed to an increase in corrosion rate. Full article

High-sensitivity detection of formaldehyde is critically important for environmental protection and public health. Zinc oxide (ZnO) is a widely used core material for chemiresistive gas sensors; however, its conventional low-index facets suffer from a limited number of active sites, creating a bottleneck for further sensitivity enhancement. To overcome this limitation, this study pioneers the application of the highly reactive ZnO $\left[20\overline{2}1\right]$ high-index polar surface for formaldehyde detection. By leveraging its unique stepped atomic configuration and unprecedented density of coordination-unsaturated active sites, we systematically investigate the formaldehyde adsorption behavior and the underlying sensing mechanism using first-principles calculations based on density functional theory (DFT). The pristine ZnO $\left[20\overline{2}1\right]$ surface exhibits intrinsic metallic character. At a coverage of 1 monolayer (ML), the most stable G1 configuration achieves an adsorption energy of −1.54 eV per CH₂O molecule. Within a 2 × 1 supercell, formaldehyde adopts both associative and dissociative adsorption modes. At a lower coverage, formaldehyde forms a stable bidentate structure through dual C–O and Zn–O bonding interactions. Electronic structure analysis reveals significant orbital hybridization and interfacial charge redistribution upon adsorption. Notably, associative adsorption opens a bandgap of 0.04 eV at the Fermi level, inducing a metal-to-semiconductor transition. In contrast, dissociative adsorption results in pronounced n-type doping, thereby elucidating the microscopic origin of the resistivity decrease observed in ZnO-based sensors. Overall, this work highlights the structural advantages of high-index facets and demonstrates for the first time the superior formaldehyde adsorption capability of the ZnO $\left[20\overline{2}1\right]$ facet, providing robust theoretical guidance for the rational design of next-generation, high-performance gas-sensing materials. Full article

The success of dental implantation depends on both mechanical stability and the host’s immune response to the implanted biomaterials. Osteoimmunology emphasizes that early immune responses at the implant-tissue interface are critical for bone healing and long-term osseointegration. The immune response primarily consists of immune cells, particularly macrophages, neutrophils, and lymphocytes, which interact with osteogenic cells through cytokine networks and signalling pathways, such as RANK/RANKL/OPG. Additionally, it modulates both bone formation and resorption. This review focuses on summarizing the mechanisms that shape the immune response around implants by dental implant materials. It describes mechanisms related to bulk composition, surface topography, and mechanical properties, and highlights macrophage polarization and the transition from inflammation to regeneration. The review discusses current immunomodulatory strategies, including bioactive surfaces, ion doping, nanopatterning, drug-releasing surfaces, and responsive materials, as well as advances enabled by additive manufacturing. The review also discusses experimental models used to study osteoimmunological interactions and the clinical significance of immune dysregulation in peri-implant diseases. The design of biomaterials based on osteoimmunology represents a shift toward immune-compatible implants that aim to improve regenerative outcomes and long-term implant success. Full article

The built-in electric field induced by polarization in ZnO/Mg_0.2Zn_0.8O quantum wells can be screened to modulate the conduction-band potential profile and intersubband energy levels. To optimize the screening of the built-in electric field, we analyze the influence of an external electric field, temperature, and modulation doping. The position of the doped layer is varied within the heterostructure to improve field compensation, providing additional control over electron localization and intersubband energy separation. In this work, within the effective mass approximation and by self-consistently solving the Poisson and Schrödinger equations using the finite-difference method, we calculate the electronic structure and nonlinear optical response of an n-type doped ZnO/Mg_0.2Zn_0.8O quantum well heterostructure. Our results indicate a strong dependence of the confinement potential on the applied external electric field and the electrostatic potential arising from the doped layer. We demonstrate electronic Raman gain values on the order of ${10}^3$–${10}^4$ cm⁻¹ for specific values of field strength, temperature, and doped-layer position. This approach enables fine-tuning of the nonlinear optical response, which is crucial for the development of ZnO-based optoelectronic devices. Full article

Tellurene has a wide bandwidth and low propagation loss at near-infrared wavelengths due to its nonlinear absorption coefficient. Therefore, we prepared tellurene–polyvinyl alcohol (Te-PVA) film as a saturable absorber in an Er-doped fiber laser by liquid phase exfoliation and spin-coating. The modulation depth was 5.25% and the saturation intensity was 17.02 MW/cm. The nonlinear optical properties of the film and its application in high-stability mode-locked operation were studied. A mode-locked pulse with a fundamental frequency of 8.48 MHz and a central wavelength of 1560.10 nm was obtained, with a signal-to-noise ratio which was greater than 75 dB. A traditional soliton mode-locked operation with a pulse width of 1.41 ps was achieved. In addition, eighth- and 19^th-harmonic mode-locked operations were obtained by adjusting the pump power and polarization controller. Our results show that Te-PVA film functioned as a saturable absorber which enabled harmonic mode-locking with an SNR of 75 dB in an Er-doped fiber laser. It is thus an excellent ultra-fast photonics material. Full article

Twist-angle engineering in van der Waals bilayers enables excitonic and valley phenomena that are not accessible in naturally stacked crystals. In a dual-gated $3^{\circ }$ twisted bilayer WSe₂ device, low-temperature polarization-resolved photoluminescence spectroscopy reveals a pronounced Stark shift of the interlayer exciton, yielding an effective electron–hole separation of 0.26 nm and indicating a strongly hybridized interlayer excitonic state. The degree of circular polarization (DOCP) is strongly doping-dependent but only weakly affected by the vertical electric field: at zero magnetic field, the DOCP is about 30% in the electron-doped regime and about 18% in the hole-doped regime. An out-of-plane magnetic field of 9 T sharpens this contrast to about 35% and 13%, respectively, suggesting distinct intervalley depolarization dynamics in the two doping regimes. Together, these results show that an electric field primarily tunes exciton energy, whereas doping and a magnetic field control valley polarization, highlighting small-angle twisted bilayer WSe₂ as a promising platform for tunable excitonic and valley-optoelectronic functionalities. Full article

Developing circularly polarized phosphorescence (CPP) materials integrating long-afterglow room-temperature phosphorescence (RTP) and chiral optical properties is highly attractive but challenging. Herein, we report a facile and efficient strategy to achieve enhanced CPP by doping chiral naphthyl phosphoric acid derivatives (BNP-CZ, BNP-DPA, BNP-TPA) into a thermally cured Bisphenol A Epoxy Resin (DGEBA) matrix crosslinked with 1,8-diaminooctane (DAO). The rigid crosslinked network effectively suppresses nonradiative transitions and stabilizes triplet excitons, affording a long phosphorescence lifetime of up to 973 ms and a high photoluminescence quantum yield of 26.55%. Significantly, the BNP-CZ@DAO exhibits remarkably boosted CPP signals and realizes the switch from circularly polarized fluorescence (CPF) in solution to CPP in the thermally cured resin film. Benefiting from the long afterglow and chiral optical properties, these polymers are successfully applied in multi-dimensional anticounterfeiting with high security. This work provides a universal and scalable approach for developing high-performance CPP materials. Full article

This study provides a rigorous analysis of the phase stability, mechanical behavior, and surface integrity of a non-equiatomic (FeCoNiCr)₈₅Ga₁₅ high-entropy alloy (HEA). By transitioning from the conventional equiatomic design to a gallium-doped 3d-transition metal matrix, we explore the interplay between lattice distortion and phase separation. Synthesized via vacuum arc melting, the as-cast alloy exhibits a non-homogeneous dendritic morphology consisting of a Cr-Fe-Co rich face-centered cubic (FCC) matrix and Ni-Ga rich body-centered cubic (BCC) interdendritic regions. While global thermodynamic criteria (δ = 3.65, ΔH_mix = −9.28 kJ/mol, and Ω = 2.23) favor single-phase solid solution stability, the Valence Electron Concentration (VEC = 7.46) precisely forecasts this dual-phase structure. Following low-temperature annealing at 250 °C for 24 h, high lattice strain energy drives a significant morphological transformation where the continuous interdendritic network resolves into discrete, phase-separated B2/BCC “islands”. Mechanical and tribological characterizations reveal that this low-temperature thermal activation triggers precipitate hardening; the macro-hardness increases from 146 ± 11 HB to 153 ± 7.5 HB and the micro-hardness rises from 186 ± 4 HV_0.5 to 206 ± 17.5 HV_0.5, yielding enhanced resistance to oxidation-delamination wear. However, electrochemical evaluation in a 3.5 wt.% NaCl solution highlights a fundamental trade-off: the formation of localized galvanic micro-cells between the phase-separated islands and the matrix causes the corrosion current density (i_corr) to increase from ≈10⁻⁹ A/cm² in the as-cast state to ≈10⁻⁶ A/cm² post-heat treatment, accompanied by a heightened susceptibility to localized pitting. These findings elucidate the primary role of electronic structure and minor p-block additions in regulating the lifecycle performance of transition metal HEAs under extreme conditions. Full article

In this study, we employed one of the green synthesis methods utilizing water extracts prepared from solid industrial wastes of Rosa damascena Mill. (RD) and Oriental variety tobacco (Nicotiana tabacum)-mixed stems and leaves (O) as a natural reducing agent for PdCl₂ to obtain environmentally friendly Pd nanoparticles (PdNPs). Transmission electron microscopy (TEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDX) in TEM were applied to determine the morphology, microstructure, phase, and elemental composition of PdNPs synthesized. The concentration of PdNPs in the suspensions was quantified by inductively coupled plasma optical emission spectroscopy (ICP-OES), which is essential for their intended application. Furthermore, the synthesized PdNPs were incorporated as dopant into a polymer matrix (PAZO) developed for optical applications. As will be demonstrated, doping PAZO with specific concentrations (0.1, 0.2, 0.25, 0.3, 0.4, 0.5, and 1 wt. %) of green PdNPs enhances the maximal value of the photoinduced birefringence by more than 50%. This improvement enables more efficient inscription of polarization-selective holographic optical elements in the resulting photoanisotropic nanocomposite materials with nearly 25% higher diffraction efficiency. Using a digital polarization holographic setup, the spatial modulation of polarization was recorded on thin nanocomposite films of the azopolymer PAZO, doped with certain concentrations of the green PdNPs. Full article

Perovskite-type oxides are among the most promising cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to their mixed ionic–electronic conductivity and compositional flexibility. Many high-performance cathodes rely on Sr substitution at the A-site, often associated with surface segregation and long-term degradation. In this work, we explore an alternative strategy based on defect engineering and phase interactions in Sr-free composites. Perovskite-fluorite composites based on LaFe_0.8Co_0.2O₃ were synthesized through a one-pot route designed to promote the formation of a perovskite phase and a limited amount of fluorite-type ceria. This approach allows the introduction of small fractions of Ce into the perovskite lattice, favoring the cooperative coexistence with La-doped CeO₂. Structural, microstructural and spectroscopic characterization indicates that Ce influences the crystallization pathway and composite defect chemistry. Variations in lattice parameters and Raman features suggest modifications of perovskite structure consistent with defect formation and lattice distortion. Reduction properties and electrical conductivity measurements indicate that Ce incorporation in the perovskite and oxide interaction affect charge transport and oxygen mobility. The electrochemical results demonstrate that the optimal trade-off between activation energy (Ea) and polarization resistance (Rp) is achieved for the sample, with a nominal cerium content, Ce/(La + Ce) of 0.16. Moreover, the electrochemical properties are found to correlate with the nominal cerium content, which regulates defect chemistry and the resulting composite composition. Overall, results suggest that the one-pot synthesis promotes beneficial interactions between the perovskite and ceria phases, allowing the development of Sr-free ferrite-based materials with enhanced functional properties, minimizing the amount of ceria in the composite. Full article