Iron silicide (β-FeSi₂) is an important semiconductor that has attracted significant attention for optoelectronic, photovoltaic, and thermoelectric applications. Its conductivity can be tuned to either n-type or p-type through doping, providing flexibility for device design. In thermoelectric (TE) applications, however, the introduction of dopants often leads to the formation of secondary metallic phases, which can degrade TE performance. The thermoelectric performance of p-type β-FeSi₂ is generally inferior to that of n-type material. Therefore, it is necessary to investigate the crystal structures and transport properties of p-type Al-doped β-FeSi₂.

The polycrystalline FeSi_2−xAl_x samples were prepared by arc melting followed by a heat treatment process to obtain the β-phase. The crystal structures were identified using X-ray diffraction, and the phase fractions were quantified by Rietveld refinement. The electrical resistivity and Seebeck coefficient were measured using both a Hall effect measurement system (ResiTest8300) and a homemade device. Thermal conductivity was measured using a power efficiency measurement system.

As a result, undoped FeSi₂ samples were initially crystallized in the ε and α-phases and transformed into a semiconducting β-phase (~97%) after heat treatment, confirming the essential role of thermal processing in β-phase formation. The unit cell volume increases with increasing Al doping level, which can be attributed to the larger atomic radius of Al compared to Si, indicating substitutional incorporation of Al into the Si sublattice. It is found that Al incorporation significantly affected secondary phase formation, reducing the β-phase fraction to below 70% for x ≥ 0.04. This result reveals a strong destabilization effect of Al on β-FeSi₂, which has not been clearly quantified in previous studies. Meanwhile, thermal conductivity decreased with increasing Al content, likely due to enhanced phonon scattering from point defects caused by Al substitution, consistent with previous reports. This study provides useful insights for material design and thermal-to-energy conversion applications.

Epitaxial thin films assume nowadays the leading role as functional material in several applications: among these, the deposition of cuprate High-Temperature Superconductors (HTSs) as modern Coated Conductors (CCs), where the epitaxial growth of the material is enabled through multiple oxide buffer layers, has led to huge advancements in the high-field magnet sector and thus fusion technology.

Iron-based superconductors (IBSs) constitute a novel class of superconducting materials, with critical temperatures in the 10 – 60 K range and extremely high critical magnetic fields. For IBS CCs, the materials' characteristics reduce the need for strict texturing, and deposition conditions are less demanding than those required for HTSs. Recently, we showed that a thin TiN film can represent an effective single buffer layer for an Fe(Se,Te) superconductor, enabling the oriented growth of high-performance films on biaxially textured Ni-W. This single buffer layer is furthermore appealing because TiN is electrically conductive. The resulting structure, fabricated by pulsed laser deposition, is characterized by simplicity and good performance.

However, several aspects require careful control, with a multi-layered system characterized by several critical interfaces: the chalcogenide and TiN are characterized by a high lattice mismatch (26 %). High-Resolution TEM images highlight, however, the epitaxy of Fe(Se,Te) on TiN, showing how a domain-matching epitaxy mechanism drives the film orientation. Moreover, the performance of the superconducting film is influenced by the structure and the presence of secondary phase inclusions at grain boundaries, affecting the regularity of the layered chalcogenide, as observed by TEM and diffraction analyses.

The results shown here unveil how different parameters influence the microstructural properties down to the atomic scale and how these are reflected in the superconducting behaviour, providing guidelines for the optimization of Fe(Se,Te) growth on simplified coated conductor architectures for a novel generation of superconducting tapes.

Introduction

Lithium niobate (LN) is a work-horse of photorefractive holography. Recently outstanding results on (Bi,Mg)-codoped congruent LN have been reported. As the photochromic effect often degrades the quality of photorefractive devices, our aim is to investigate the dynamics and mechanism of photochromism and photorefraction in (Bi,Mg)-codoped stoichiometric LN, separating their effects on the diffraction efficiency in two-wave mixing experiments.

Methods

Czochralski-grown samples with a Li/Nb ratio of 1.38:1, Bi concentrations of 2 or 4 mol%, and Mg concentrations of 1 or 2 mol% (all data in the melt) were used to investigate both photochromic and photorefractive effects at 405 and 443nm at temperatures between 10 and 45°C. A two-wave mixing simulator program was developed based on a one-center model involving photochromic and various photorefracive mechanisms.

Results

Apart from persistent light-induced absorption reported earlier [1] and small transients on the ms timescale, an important photochromic component was found to be saturating on a subsecond and decaying on a subminute timescale, the recovery governed by an activation energy of ~0.6eV. Photorefractive response was faster with τ≈30ms. The ratio of the photorefractive and photochromic diffraction efficiencies was determined as a function of the input intensity, showing the domination of the photorefractive one for total input intensities above some tens of mW/cm². Estimates of the recombination coefficient and the effective cross-section for electron excitation by photon absorption could be derived.

Conclusions

Despite its pronounced photochromism, LN:(Bi,Mg) is an efficient and fast photorefractive material, even at low intensities. This is due to various Bi-defect complexes promoted by Mg-codoping, introducing localized ground and higher pinned-exciton (exciton-polaronic) levels in the gap, both serving as potential donors [1]. The results are helpful for optimizing holographic systems and obtaining a better understanding of the microscopic behavior of LN:(Bi,Mg).

[1] L. Kovács et al., Phys. Rev. B 109, 214105 (2024)

Inorganic materials with layered architectures are made up of stacked atomic or molecular layers held together by weak van der Waals interactions. Examples of such materials include layered perovskites, clays, MXenes, transition metal dichalcogenides, layered double hydroxides, and carbon-based layered materials. The intercalation of various guest species (e.g., nanoparticles, molecules, polymer chains) into lamellar inorganic compounds is an effective strategy for creating multifunctional materials with enhanced physical and chemical properties relative to those of the parent compounds. Exfoliation of layered nanostructures into single nanosheets yields soft materials with distinct features. The intercalation process is affected by several critical factors, including interlayer distance, guest orientation in the interlayer space, and/or layer rigidity. Tailoring these factors enables the creation of high-performance intercalated materials with applications across energy storage, electronic devices, sensors, catalysis, and nanotechnology.

Herein, we report a soft chemical approach to intercalating copper species into the RbLaTa₂O₇ layered perovskite tantalate involving a copper halide precursor at a mild temperature. Both unmodified and (CuCl)⁺-intercalated layered perovskite were characterized using multiple techniques to assess structural, optoelectronic, and morphological changes. The shifting of the (001) diffraction line confirmed the successful insertion of (CuCl)⁺ species in between the perovskite layers. The FTIR technique validated structural modifications in the materials. UV-Vis spectroscopy demonstrated a decrease in the band gap of the (CuCl)⁺-intercalated layered tantalate, thereby enabling visible-light absorption. Preliminary photocatalytic performance evaluations indicate that (CuCl)⁺-based perovskite exhibits promising activity for phenol degradation, serving as an effective catalyst for environmental applications.

Acknowledgements. The authors thank the Inter-academic exchange project between the Romanian Academy and the Hungarian Academy of Sciences, Nr. Reg. A.R. 4389/25.09.2025; period: 2026 – 2028.

Introduction:
Green synthesis has emerged as an environmentally sustainable alternative to conventional chemical approaches for nanoparticle production. Fungal-mediated biosynthesis of silver nanoparticles (AgNPs) is particularly promising due to its efficiency in metal ion reduction and natural secretion of stabilizing biomolecules. This study examined whether stimulating phenol oxidase activity in culture media enhances the rate and yield of AgNP formation using the filamentous fungus Aspergillus niger.

Methods:
Six variants of Czapek–Dox medium were prepared using sucrose, starch, or glucose as carbon sources. Phenol oxidase stimulation was introduced into variants 2, 4, and 6 through copper(II) sulfate, oak sawdust, and hydrogen peroxide. A. niger was cultivated for 72 h in each medium, after which the biomass was transferred to ultrapure water for extracellular metabolite release. Following another 72 h, the biomass was removed, and a 1 mM silver nitrate solution was added to the filtrates. AgNP formation was monitored by UV–Vis spectroscopy over 120 h. Functional groups were identified by FTIR, and crystalline structure was confirmed using XRD.

Results:
A characteristic AgNP surface plasmon resonance peak at ~420 nm appeared in all variants. Media containing phenol oxidase stimulants showed notably higher absorbance and faster nanoparticle formation kinetics. FTIR spectra confirmed the presence of protein, enzyme, and carbohydrate functional groups involved in nanoparticle capping, while XRD verified the crystalline nature of the AgNPs across all samples.

Conclusions:
Phenol oxidase stimulation significantly enhanced the rate of AgNP biosynthesis without altering the nanoparticle structure or capping composition. Medium optimization, therefore, represents a critical step toward scaling fungal-based AgNP production for industrial applications.

Tetragonal tungsten bronzes (TTBs) represent an important class of functional ceramics, known for their high dielectric properties and thermal stability. Tailoring the properties of these materials through ionic substitution enables modulation of the crystal structure and, consequently, their electrical performance. In this context, the study of solid solutions A₂(Sm₁₋ₓREₓ)Ti₂Nb₃O₁₅ (A = Sr, Ba; RE = Nd, Sm, Gd, La) provides an ideal framework to examine the influence of rare-earth ionic radii on the TTB structure and its dielectric properties, offering key insights for the development of high-performance ceramics.

The compounds A₂(Sm₁₋ₓREₓ)Ti₂Nb₃O₁₅ (A = Sr, Ba; RE = Nd, Sm, Gd, La) were synthesized via solid-state reaction. The resulting ceramics were characterized using various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and dielectric measurements. Substitution with different rare-earth elements in the TTB compounds leads to a gradual decrease in lattice parameters as the ionic radius decreases (from La to Gd), accompanied by a space group transition from P4bm for La, Sm, and Nd to P4/mbm for Gd. Dielectric properties show significant variation depending on the rare-earth element, with high dielectric constants and low losses, reflecting the influence of local polarization and structural distortions. SEM observations reveal changes in grain morphology and size consistent with the effects induced by ionic substitution. Overall, these results highlight a direct correlation between the RE ionic radius, lattice distortions, and dielectric properties, confirming the crucial role of substitution chemistry in tuning the properties of tetragonal tungsten bronzes.

Introduction:
Coumalic acid (2H-pyran-2-one-5-carboxylic acid) is an oxygen-rich heterocyclic compound containing both carboxylic and lactone functional groups, making it a suitable ligand for coordination with metal ions. Zinc(II), a d¹⁰ metal center with a preference for oxygen donor atoms, readily forms stable complexes with carboxylate-containing ligands. Studying Zn(II)–coumalic acid interactions provides insight into coordination behavior, ligand binding modes, and structural diversity. This study investigates the formation of zinc(II) complexes using nitrate and acetate precursors.

Methods:
Zinc(II) complexes were synthesized by reacting aqueous solutions of zinc(II) nitrate hexahydrate and zinc(II) acetate dihydrate with coumalic acid under ambient conditions. The resulting solids were isolated and characterized by FTIR, PXRD, TGA/DSC, and UV–Vis spectroscopy. These techniques were used to evaluate coordination modes, structural features, thermal stability, and solution behavior. A comparative analysis of nitrate- and acetate-derived systems was conducted.

Results:
Complex formation was confirmed in both systems, indicating effective coordination through oxygen donor atoms. Spectroscopic data suggest that coordination primarily involves the deprotonated carboxylate group, with possible participation of the lactone carbonyl oxygen. Coumalic acid may act as a mono- or bidentate ligand, enabling the formation of stable coordination motifs. The obtained solids exhibit characteristic spectroscopic features and thermal behavior consistent with coordinated zinc(II) systems.

Conclusions:
Zinc(II) forms stable complexes with coumalic acid through coordination involving oxygen donor atoms, predominantly from the carboxylate group. The results highlight the ligand’s versatility and its ability to support different coordination modes, contributing to the structural diversity of Zn(II) complexes.

Funding:
This research was funded by the European Union-NextGenerationEU Project “Advanced Interdisciplinary Approaches to Environmental Chemistry: From Materials to Sustainable Solutions for Pollution” (Grant number: 581-UNIOS-101).

Introduction:
Calcium oxalate (CaOx) is the dominant mineral phase in human kidney stones, making the understanding of its nucleation, growth, and phase selection essential for elucidating urolithiasis mechanisms. Phthalate esters are ubiquitous plasticizers with diverse hydrophobic and steric properties, and rising human exposure has increased interest in their potential interactions with urinary constituents. This study investigates how structurally distinct phthalates (DIDP, DINP, DEHP, DNOP, BBP, DBP, DIBP) influence CaOx precipitation under physiologically relevant conditions.

Methods:
CaOx was precipitated in aqueous media in the presence or absence of individual phthalates under controlled conditions (pH 6.5, ionic strength 0.05 M, 37 °C). Crystal morphology was assessed using light microscopy, and phase composition was determined by PXRD and FTIR.

Results:
In the additive‑free system, crystallization yielded exclusively COT, with crystals uniformly dispersed throughout the solution. In contrast, all phthalate-containing systems exhibited pronounced aggregation of crystals around hydrophobic additive domains. This aggregation was accompanied by clear morphological alterations, including variations in crystal dimensions and habit. While most phthalates had no measurable impact on phase composition, DINP uniquely induced partial transformation from COT to the thermodynamically more stable calcium oxalate monohydrate, indicating a structure-dependent effect on CaOx stability.

Conclusions:
Phthalate esters consistently promoted crystal aggregation and induced morphology changes, supporting predominantly surface‑mediated interactions influenced by molecular size, hydrophobicity, and chain branching. DINP was the only compound capable of modifying CaOx phase stability, likely due to its branched isononyl structure perturbing the hydration environment of COT. These findings indicate that aggregation is a common response to all tested phthalates. However, more detailed investigations are required to fully clarify the underlying mechanisms.

Funding:

This research was funded by the European Union—NextGenerationEU. Project “Advanced Interdisciplinary Approaches to Environmental Chemistry: From Materials to Sustainable Solutions for Pollution” (Grant number: 581-UNIOS-101).

The quasi-ternary system Ag₂S−Sb₂S₃−GeS₂ is of interest since the initial binary compounds and ternary compounds Ag₃SbS₃, AgSbS₂, Ag₈GeS₆, Ag₁₀Ge₃S₁₁ and Ag₂GeS₃ of the limiting quasi-binary systems exhibit promising properties for applications in solar energy, thermoelectricity, optoelectronics and biomedicine.

The samples for the study of the Ag₂S–Sb₂S₃−GeS₂ system were obtained by direct single-temperature synthesis from high-purity (at least 99.99 wt.%) elements silver, antimony, germanium and sulfur in evacuated quartz containers. The ampoules were heated to the maximum synthesis temperature of 1220 K, cooled to 500 K, annealed at 500 K for 500 h, and then quenched in air.

The identification of the synthesized samples employed X-ray phase analysis, microstructure analysis, and differential thermal analysis.

Two compounds are formed in the Ag₂S−Sb₂S₃−GeS₂ system at 500 K, Ag₁₁Sb₃GeS₁₂ (intersection of AgSbS₂–Ag₈GeS₆ and Ag₃SbS₃–Ag₂GeS₃ sections) and Ag₂₃Sb₃Ge₇S₃₀ (intersection of Sb₂S₃–Ag₁₀Ge₃S₁₁ and Ag₃SbS₃–Ag₂GeS₃ sections). The isothermal section thus consists of eight two-phase equilibria on the boundary sides, and eleven in the middle of the quasi-ternary system, separating ten three-phase fields.

Vertical section Ag₃SbS₃–Ag₂GeS_3,which is a quasi-binary system, was investigated. Both quaternary compounds Ag₁₁Sb₃GeS₁₂ and Ag₂₃Sb₃Ge₇S₃₀ form at this section at 25 mol.% Ag₂GeS₃ and 70 mol.% Ag₂GeS₃, respectively, and melt congruently at 1047 K and 1077 K, respectively. Ag₁₁Sb₃GeS₁₂ has two polymorphous transitions at 527 K and 605 K; Ag₂₃Sb₃Ge₇S₃₀ has a polymorphous transition at 880 K.

The crystal structure of both compounds was determined by powder XRD. Ag₁₁Sb₃GeS₁₂ (Ag_0.917Ge_0.083Sb_0.250S) crystallizes in cubic space group F-43m, and Ag₂₃Sb₃Ge₇S₃₀ (Ag_1.600Ge_0.400Sb_0.268S₂) crystallizes in tetragonal space group I-42d.

The rapid rise of antimicrobial resistance poses a critical threat to global health, accounting for more than 35,000 deaths annually across the EU, Iceland, and Norway alone. This escalating burden necessitates the development of innovative antimicrobial materials that can overcome the limitations of conventional approaches. Unlike antibiotic-releasing coatings, metal oxide nanoparticles (NPs) offer durable, long-term antimicrobial activity without inducing resistance, positioning them as a promising next-generation solution. Their high physicochemical stability, robustness, and low cytotoxicity further support their integration into biomedical and surface-coating applications. Among these, copper oxide (CuO) and zinc oxide (ZnO) nanoparticles stand out due to their strong intrinsic antimicrobial activity and biological relevance as essential trace elements [1,2].

In this work, we present a systematic investigation of mono- and multicomponent nanoparticle systems, including CuO, ZnO, Y₂O₃, and multimetallic Cu–Zn–Y oxide nanoparticles. The nanomaterials were synthesised using a controlled approach based on different anionic precursors, with tannic acid acting as a stabilising and structure-directing agent.

The antibacterial performance of the prepared nanoparticles was evaluated against Staphylococcus aureus, revealing pronounced antimicrobial activity across all systems, with clear differences linked to structural and compositional variations. The results demonstrate that nanoparticle size, morphology, and surface chemistry are key determinants of antibacterial efficiency, while multimetallic Cu–Zn–Y nanoparticles exhibit enhanced tunability and potential for synergistic effects.

Overall, this study provides new insights into the structure–activity relationships governing nanoparticle-mediated antibacterial effects, and establishes a rational framework for the design of advanced, biocompatible antimicrobial coatings. The findings highlight the potential of multimetallic nanoparticle systems as versatile platforms for next-generation biomedical and surface-engineering applications.

The authors acknowledge Croatian Science Foundation support through the UIP project BIO-METONIC.

References

1 .Matijaković Mlinarić, N. et al. , ACS Appl. Nano Mater. 7, 12550–12563 (2024).

2. Matijaković Mlinarić, N. et al. Nanomaterials 14, 570 (2024).