Iron-based superconductors, discovered in 2008, have attracted considerable attention due to their promising superconducting properties and their potential for high-field applications.

They share a FeAs or FeSe structural building blocks and exhibit a wide variety of structural families. Among them, the 1144 phase (AAeFe₄As₄ A=Alkaline and Ae=Alkaline earth metal), discovered in 2016, has attracted particular interest due to its robust superconducting properties. Within this family, CaKFe₄As₄ is considered one of the most promising compounds. The synthesis of these materials in polycrystalline form, relevant for superconducting wire applications, strongly affects their superconducting performance. In particular, intergrain properties, secondary phases, grain-boundary chemistry, and microstructural features such as porosity and density play a crucial role.

Chemical substitutions have been explored to optimize its superconducting properties, with partial replacement of Ca and K by elements with similar ionic radius (Na, La, Pr, Sr, and Ba). Previous studies on polycrystalline samples suggested that doping induces lattice distortions affecting the superconducting critical temperature (T_c), and enhancing the critical current density (J_c), although microstructural effects could not be excluded.

To distinguish intrinsic effects from microstructural contributions, single crystals of pristine and doped CaKFe₄As₄ were grown and investigated by single-crystal X-ray diffraction, from which the corresponding CIF files were obtained. Complementary morpho-structural and superconducting measurements were also performed to correlate the crystal structure with the physical properties.

The combined analysis highlights a clear correlation between structural modifications and superconducting behavior. Furthermore, the structural analysis suggests that defects introduced by doping act as effective pinning centers, explaining the observed enhancement of J_c.

In this work, we investigate the hysteresis behavior of a bilayer graphene system composed of mixed spins S = 7/2 and σ = 1/2 interacting through ferrimagnetic coupling. The system is described by a modified Blume–Capel Hamiltonian that incorporates both intra-layer and inter-layer exchange interactions (J1, J2, J3), as well as a uniaxial crystal field D and an external magnetic field. To analyze the magnetic properties, we employ Monte Carlo simulations based on the Metropolis algorithm, which allows us to explore the thermal and magnetic responses of the system in detail.

Particular attention is given to the effects of key physical parameters, including exchange interactions, crystal field, and temperature, on the hysteresis behavior. The obtained results reveal that the shape, size, and nature of the hysteresis loops are strongly dependent on these parameters. In particular, increasing temperature leads to enhanced thermal fluctuations, resulting in a gradual reduction in the hysteresis loop area. Above a certain critical temperature, the loops completely disappear, indicating a transition from a ferrimagnetic ordered phase to a paramagnetic state.

Moreover, variations in exchange interactions and crystal field significantly influence important magnetic characteristics such as coercivity, remanent magnetization, and loop symmetry. These findings are in good agreement with previous studies on multilayer magnetic systems and demonstrate the crucial role of competing interactions in determining the magnetic behavior.

Overall, this study provides valuable insights into the tunability of hysteresis properties in bilayer graphene systems, which could be useful for future applications in spintronics, particularly in the design of multistate magnetic memory devices.

In recent years, perovskite solar cells have been expected to become an alternative to silicon solar cells due to their high-power conversion efficiency and low production costs. However, the formation of PbI₂ during long-term storage, the resulting decrease in conversion efficiency, and the decrease in FF due to defects in the perovskite layer are challenges. In this study, rare-earth co-doped perovskite solar cells (Ce, Nd, Gd, Er, Yb) were fabricated to address these challenges. Rare earth elements are characterized by high localization of 4f orbitals and strong Lewis acidity. A decrease in trap density was observed in the Gd-doped device. In addition, an increase in the (100) orientation and an increase in crystal size were observed after ~4 months of storage at room temperature and humidity in a dark place. As a result, the fill factor increased to 0.640. In addition, the Gd-doped device was stored in a dark room at room temperature and humidity for ~4 months, and the conversion efficiency was greatly maintained without degradation. This study shows that rare-earth-doped perovskite solar cells are effective in suppressing PbI₂ formation due to long-term storage, the resulting decrease in conversion efficiency, and the reduction in FF due to grain boundary defects, providing a new strategy for perovskite solar cells.

Abstract (≈250 words)

A comprehensive study was conducted on the phase structure, microstructure, dielectric properties, and nonlinear current–voltage (J–E) behavior of doped CaCu₃Ti₄O₁₂ (CCTO) ceramics prepared using the conventional solid-state reaction method. The investigated compositions, including pure CCTO and Zr/rare-earth co-doped samples (Zr–Sc, Zr–Sm, Zr–Gd, and Zr–La), were sintered at 1080 °C for 8 h. X-ray diffraction analysis confirms that all ceramics crystallize in a cubic perovskite structure with the space group Im–3, indicating that the crystal structure remains stable after doping.

Microstructural observations reveal the formation of dense ceramics with a significant reduction in grain size as a result of Zr/rare-earth substitution. This grain refinement plays an important role in modifying the electrical behavior of the materials. Dielectric measurements show that the doped ceramics maintain a high relative permittivity (ε′ > 3.5 × 10³). In particular, the Zr–Sc composition exhibits excellent thermal stability, with a permittivity variation (Δε′) of less than ±15% up to 160 °C. Additionally, the dielectric loss (tanδ) is significantly reduced to 0.02 at 0.1 kHz at room temperature.

A remarkable enhancement in the breakdown electric field is also observed, reaching values more than 38 times higher than that of pure CCTO in the Zr⁴⁺/Sc³⁺ co-doped composition. Furthermore, the doped ceramics exhibit an energy efficiency exceeding 98%, demonstrating their strong potential for high-efficiency energy storage applications. These improvements in dielectric and nonlinear properties are mainly attributed to the increase in grain boundary resistance (Rgb), which is closely related to the reduction of oxygen vacancies in the doped ceramics.

Hydrogen (H₂) is regarded as a significant and environmentally sustainable energy carrier due to its high energy efficacy, zero toxicity, and pollution-free combustion, making it a potential long-term substitute for fossil fuels. However, efficient hydrogen storage remains a challenge. Among chemical hydrides, sodium borohydride (NaBH₄) is attractive due to its high hydrogen content (10.8 wt%) and environmentally favorable hydrolysis products. Nevertheless, its hydrolysis in water is slow and requires efficient catalysts to enhance hydrogen generation. Herein, cobalt-phosphorus (Co-P) catalysts with varying phosphorus contents were investigated for hydrogen generation via the hydrolysis of alkaline NaBH₄ solutions. The catalysts were fabricated on copper substrates through an electroless metal plating technique, with sodium hypophosphite (NaH₂PO₂) utilized as the reducing agent. The Co-P catalysts with different P amounts of 3, 5, 8, and 11 wt.% were obtained. The morphology, structure, and elemental composition of the prepared catalysts were characterized using a variety of analytical techniques, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS).

The hydrogen generation rate was evaluated in a solution containing 5 wt.% NaBH₄ and 0.4 wt.% NaOH at temperatures ranging from 313 to 343 K. The results indicate that Co-P catalysts have notable catalytic activity toward the hydrolysis of NaBH₄. The hydrogen generation rate exhibited a range from 1 to 10 L min^-1 g^-1 at 343 K, while the activation energy demonstrated a range from 49 to 85 kJ mol^-1, dependent on the phosphorus content. Specifically, the Co-P catalyst containing 11wt.% phosphorus was identified as the most efficient catalyst, exhibiting a hydrogen generation rate of 10.05 L min^-1 g^-1 at 343K. The excellent catalytic performance and cost-effectiveness of the electroless-deposited Co-P catalysts highlight their potential for efficient hydrogen production via NaBH₄ hydrolysis.

Plasmon-assisted photocatalysis often suffers from spatial nonuniformity in electromagnetic energy distribution, leaving significant portions of adjacent catalytic coatings weakly activated. A more effective approach involves modes that confine energy uniformly along the entire metal–catalyst interface. In the present research, we propose using Poynting vector vortices (PVVs) for photocatalytic activation. These vortices arise from surface plasmon polariton-like waves that circulate along the nanorod boundaries, analogous to whispering-gallery modes [1,2], and distribute electromagnetic energy uniformly around the rod perimeter. Unlike asymmetric excitations that localize fields on the illuminated side, these modes create a homogeneous electromagnetic environment along the full interface, which is particularly beneficial for activating conformal photocatalytic coatings.

We investigate these PVV modes in periodic arrays of Au and Ag nanorods coated with a photocatalytic film and supported on a dielectric SiO2 substrate. Using full-field finite-element simulations, we characterize the emergence of these PVV modes and evaluate the optical power dissipated within the surrounding catalytic layer. The circulating energy flow establishes a chiral electromagnetic topology that introduces local optical handedness even in geometrically symmetric structures. Such chiral field distributions may be relevant for catalytic processes sensitive to electromagnetic handedness, including emerging approaches to enantioselective photochemistry [3]. These findings highlight the potential of PVV modes for achieving more uniform and controllable photocatalytic activation across extended metal–catalyst interfaces.

[1] Cole, R. M., et al. "Easily coupled whispering gallery plasmons in dielectric nanospheres embedded in gold films." Physical review letters 97.13 (2006): 137401.

[2] Chen, Yongpeng, et al. "Recent progress on optoplasmonic whispering‐gallery‐mode microcavities." Advanced Optical Materials 9.12 (2021): 2100143.

[3] Goerlitzer, Eric Sidney Aaron, et al. "Molecular-induced chirality transfer to plasmonic lattice modes." ACS photonics 10.6 (2023): 1821-1831.

New oxovanadium(V) Schiff base complexes were successfully synthesized and characterized as potential catalytic materials for environmentally friendly oxidation processes. Two dinuclear water-soluble oxovanadium(V) complexes, [(L1H)VO(μ-O)]₂ (C1) and [(L2H)VO(μ-O)]₂ (C2), were prepared by refluxing vanadyl sulfate (VOSO₄) with the corresponding tetradentate Schiff base ligands in methanol under controlled conditions. The formation of the complexes was confirmed using several physicochemical characterization techniques, including Fourier-transform infrared spectroscopy (FT-IR), UV–visible spectroscopy, and elemental analysis, which provided evidence for the coordination of the Schiff base ligands to the vanadium center.

The catalytic performance of the synthesized complexes was evaluated in the oxidation of olefins in aqueous medium. Water was employed as a green and environmentally benign solvent in order to develop a more sustainable catalytic process. Different oxidizing agents were investigated to determine their influence on catalytic efficiency and product selectivity. The results demonstrated that the oxovanadium(V) complexes exhibit high catalytic activity toward olefin oxidation, affording excellent product yields under mild reaction conditions. Furthermore, the catalysts showed remarkable stability and recyclability, maintaining their catalytic performance over several successive reaction cycles without significant loss of activity.

These findings highlight the potential of dinuclear oxovanadium(V) Schiff base complexes as efficient and sustainable catalysts for oxidation reactions. The use of water as a solvent and the good recyclability of the catalysts make these systems promising candidates for green catalytic processes and environmentally friendly chemical transformations with potential relevance to energy-related and sustainable chemistry applications.

In recent years, doped half-Heusler compounds have attracted significant attention due to their tunable electronic, magnetic, and transport properties, making them promising candidates for spintronics applications. In this work, we investigate the effect of magnetic Mn doping on the structural stability, electronic structure, magnetism, and intrinsic anomalous Hall effect of the half-Heusler compound HfPtSi using first-principles density functional theory (DFT) calculations. Phonon dispersion calculations confirm the dynamical stability of both pristine and Mn-doped HfPtSi. The calculated electronic band structure shows that pristine HfPtSi exhibits semiconducting behavior. However, substitution of Mn at the Hf site significantly modifies the electronic structure and induces a ferromagnetic ground state with a magnetic moment of 3 μB per unit cell. As a result, the doped system exhibits half-metallic behavior, where the spin-up channel becomes metallic while the spin-down channel remains insulating. The emergence of ferromagnetism together with strong spin–orbit coupling (SOC) gives rise to a pronounced anomalous Hall effect originating from enhanced Berry curvature near the Fermi level. The calculated anomalous Hall conductivity reaches approximately 200 Ω⁻¹ cm⁻¹ at the Fermi level and increases to about 500 Ω⁻¹ cm⁻¹ at 100 meV above the Fermi level, which is comparable to several reported half-metallic ferromagnets. These results suggest that Mn-doped HfPtSi is a promising candidate for next-generation spintronic devices.

The synthesis methodologies and reaction parameters directly affect the structure and morphology of materials such as perovskite-type compounds. In this work, sodium niobate (NaNbO₃) was produced using the combined EDTA/citrate complexation method, with ratios of 1:1:3 metal ions (sodium and niobium): EDTA: citric acid, and pre-treatment at 230 °C and temperature calcination at 700 °C. The sample was analyzed using XRD with Rietveld refinement and UV-Vis ERD. The study revealed that the material has an orthorhombic crystal structure and P2₁ma space group identified by CIF 9014103. Based on the atomic positions obtained from Rietveld refinement, it was observed that each NaNbO₃ sample maintained a basic perovskite network, particularly the BO₆ polyedra centered on the niobium cation site, with lattice parameters of a = 5.565Å, b = 7.774 Å and c = 5.521 Å. The crystallite size of sodium niobate was obtained using a Scherrer-type relationship, with a value of 169.91 nm. But the synthesis method promoted significant distortions within the NbO₆ coordination polyhedra. The bandgap value obtained was 2.69 eV, which is lower than those reported in the literature (~3.4 eV). These variations can be attributed to changes in the crystalline structure and particle morphology, which may undergo phase transitions that affect their electronic properties and, consequently, their bandgap. Therefore, the synthesis method used is effective in producing NaNbO₃ with tunable properties, expanding its potential for technological applications such as hydrogen production and storage.

Iron silicide is an earth-abundant and environmentally friendly material system that crystallizes in several phases, including metallic ε-FeSi and α-Fe₂Si₅, and semiconducting β-FeSi₂. Among them, β-FeSi₂ has attracted considerable interest for optoelectronic, photovoltaic, and thermoelectric applications due to its tunable electrical conductivity. Both n-type and p-type conduction can be achieved through transition-metal doping; however, performance optimization is often limited by dopant solubility and the emergence of secondary metallic phases. Previous studies mainly inferred solubility limits from lattice parameter shifts or qualitative phase identification, with a lack of quantitatively correlating bulk phase fractions and local elemental distribution.

Polycrystalline Fe_1−xM_xSi₂ (M = Mn, Co, Ni) samples were prepared by arc melting followed by a two-step heat treatment to promote the formation of the β phase. Dopant concentrations were systematically varied within controlled ranges. Phase identification and quantitative analysis were performed using X-ray diffraction combined with Rietveld refinement, while microstructure and elemental distributions were examined by SEM-EDS at multiple locations to evaluate reproducibility and local dopant incorporation.

The evolution of phase fractions reveals that increasing dopant concentration promotes the formation of metallic ε and α-phases. Although the β-phase remains dominant (>95%) over a finite composition range, local compositional analysis indicates earlier saturation of dopant incorporation within the β-matrix. The estimated solid-solution limits are approximately 6.3% for Mn and 8.8% for Co, while Ni exhibits significantly lower solubility. Beyond these limits, excess dopants segregate and contribute to metallic phase formation, which correlates with degradation in thermoelectric performance. The combined bulk and local analyses provide a practical strategy to evaluate dopant solubility and phase stability in β-FeSi₂, offering guidance for optimizing transition-metal doping in semiconductor-based energy materials.