Scientific highlights

 
Nuclear magnetic resonance (NMR) is an exceptional technique that has wide applications in science, medicine and industry. NMR spectroscopy is used, for example, to characterize new anticancer drugs or to study the treatment of nuclear waste. Paramagnetic NMR (pNMR) spectroscopy is an extremely useful technique for the characterization of paramagnetic substances, while NMR spectroscopy is traditionally used to investigate diamagnetic substances. However, these two techniques are closely linked by the hyperfine interaction between electrons and nuclei in paramagnetic systems. In this work, we describe the elementary theory behind the hyperfine interaction and pNMR shifts. We divide the overall pNMR shift into three fundamental physical mechanisms: Fermi-contact (FC), paramagnetic spin-orbital (PSO) and spin-dipolar (SD). And we discuss recent progress in understanding the structural and electronic principles underlying these mechanisms.
Even after decades of progress in the analysis of pNMR spectra, their interpretation still lags behind that of NMR spectra of diamagnetic substances. This work is a step towards alleviating this imbalance and leading to a deeper understanding of the chemical concepts underlying hyperfine interaction and its manifestation in paramagnetic NMR spectra.
 

Publication:

• NOVOTNY, Jan – KOMOROVSKÝ, Stanislav** – MAREK, Radek**. Paramagnetic Effects in NMR Spectroscopy of Transition-Metal Complexes: Principles and Chemical Concepts. In Accounts of chemical research. Reviews, 2024, vol. 57, no. 10, pp. 1467−1477. (2023: 16.4 – IF, Q1 – JCR, 5.948 – SJR, Q1 – SJR). https://doi.org/10.1021/acs.accounts.3c00786 Typ: ADCA

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Mnt as a natural material and POxs as biodegradable polymers are environmentally friendly, and therefore nanomaterials consisting of these components appear to be promising for various applications. In this work, the adsorption capacities of hybrid systems of montmorillonite and nonionic polymers, three poly(2-alkyl-2-oxazoline) (POxs) with different alkyl chain lengths, were systematically studied for the first time. The adsorption isotherms of the polymers showed a sharp increase in adsorption at low contents of the polymers used for modification. When the Mnt surface was saturated with POxs, a plateau appeared on the adsorption curve and the amount of polymer in the nanocomposite did not change any more. The structural characteristics of the prepared nanocomposites were studied using XRD and FT-IR methods. With increasing amount of polymer, the interlayer space of Mnt increased up to a polymer content in the nanocomposite of 6.0 mmol g–1, at higher amounts it practically did not change. Adsorption capacity is an important parameter in the design of nanocomposite materials. By knowing the limiting amount of polymer, it is possible to better adapt the conditions of material preparation, and thus influence the functionality of the nanocomposite for a specific application.

Publication:

• PRIBUS, Marek** – JANKOVIČ, Ľuboš – KUREKOVÁ, Valéria – BARLOG, Martin – MADEJOVÁ, Jana. Intercalation Characteristics of Montmorillonite Modified with Poly(2-n-alkyl-2-oxazoline)s. In Macromolecules, 2024, vol. 57, no. 17, p. 8362–8373. (2023: 5.1 – IF, Q1 – JCR, 1.401 – SJR, Q1 – SJR). https://doi.org/10.1021/acs.macromol.4c00291

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Developing high-performing phosphors for white light LED sources is a rapidly advancing field of luminescence research. This study presents the synthesis of novel Eu-doped Y₃Al₅O₁₂ (YAG) phosphors through a sol-gel method and flame synthesis process, leading to an amorphous microsphere. This allows the reduction of Eu³⁺ to Eu²⁺ in an amorphous state at a significantly lower temperature (800 °C) than traditional ceramic methods (1600 °C).
The emission spectrum of the YAG:Eu²⁺ phosphor in microspheres exhibited a wavelength covering the visible light spectrum – a range spanning from 450 to 800 nm, with a prominent peak at 565 nm.

Publication:

• GHADAMYARI, Marzieh – KLEMENT, Róbert – HOSSEINI, Hossein Ebrahim – PARCHOVIANSKÝ, Milan – KRAXNER, Jozef – GALUSEK, Dušan – NARAYANASAMY, Sathya – HACK, Erwin – BLUGAN, Gurdial – MICHÁLKOVÁ, Monika. Preparation and characterization of YAG microspheres doped with Eu2+/Eu3+ for broad band emission. In Open Ceramics, 2024, vol. 19, art no. 100654. (2023: 2.9 – IF, Q1 – JCR, 0.534 – SJR, Q2 – SJR). https://doi.org/10.1016/j.oceram.2024.100654 Typ: ADMA

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Synthesis and characterisation of the new mixed-cation fluorides KNa₂ZrF₇ and KNa₂HfF₇ (refined composition KNa₂Hf_0.44(1)Zr_0.56(1)F₇), together with isostructural KNa₂ZrF₇ (space group Pmn2₁), are presented in this work. The compounds have been obtained from aqueous solutions and structurally analysed at room temperature by powder and single-crystal X-ray diffraction. The solid-solid phase transformations have been revealed during the differential scanning calorimetry experiments and further confirmed by temperature-dependent X-ray powder diffraction. It has been found that the mixed-cation phases Na₂KZrF7_{, Na2KHfF7 and Na2K(Zr,Hf)F7 undergo irreversible phase transformations, which can be explained by their decomposition over 673 K.}

Publication:

MATSELKO, Oksana** – POUPON, Morgane – SAMOLOVA, Erika – VASKOVÁ, Zuzana – KUBÍKOVÁ, Blanka – NETRIOVÁ, Zuzana – MIČUŠÍK, Matej – BOČA, Miroslav. Complexity of the KNa₂ZrF₇, KNa₂HfF₇, and KNa₂(Hf,Zr)F₇ compounds. In Journal of Solid State Chemistry, 2024, vol. 334, art no. 124655. (2023: 3.2 – IF, Q2 – JCR, 0.6 – SJR, Q2 – SJR). https://doi.org/10.1016/j.jssc.2024.124655 Typ: ADCA

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A simple method for producing pseudo-ternary eutectic ceramic composites has been developed. Bulk ceramic composites based on Al₂O₃-Al₃Y₅O₁₂-ZrO₂, featuring various microstructural characteristics, were prepared using spark plasma sintering (SPS) of ceramic powders synthesized by Pechini’s method.
The calcination temperature and duration, as well as the SPS program, were found to influence the microstructural features of the bulk composites. The powders were calcined at temperatures ranging from 900°C to 1200°C for up to 5 hours. The bulk composites were then created through spark plasma sintering at temperatures between 1000°C and 1500°C, with a dwelling time of 1 to 10 minutes.

Patent application:

• Vakhshouri M., Najafzadehkhoee A., Talimian A., Galusek D., A method for producing eutectic ceramics composites based on the pseudo-ternary system of Al₂O₃-Al₃Y₅O₁₂-ZrO₂, Data number: 1000048537, Industrial Property Office of the Slovak Republic, Filed date: 30 January 2024.

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Advanced carbon materials for energy applications often contain nitrogen, which affects their properties. Conventional analytical techniques for nitrogen provide limited information, which makes material design difficult. An advanced technique called temperature-programmed desorption (TPD) has been developed up to 2,100 °C [1]. Using X-ray photoelectron spectroscopy, elemental analysis and model simulations, it was found that the gas emissions provide information about the composition and structural type of nitrogen. TPD allows for the quantification of nitrogen at the 10 ppm level, which is two orders of magnitude more sensitive than conventional methods and provides the basis for a new generation of research focusing on structural design at the ppm level with significant potential for industrial applications. Model simulations performed at the Institute of Advanced Studies in the Slovak Academy of Sciences using the DFT method significantly contributed to the reliable validation of the results obtained by the new TPD technique at Tohoku University in Japan. The models simulated the gas release processes for different structures surrounding nitrogen in graphene.

Publication:

• YOSHII, Takeharu** – NISHIKAWA, Ginga – PRASAD, Viki Kumar – SHIMIZU, Shunsuke – KAWAGUCHI, Ryo – TANG, Rui – CHIDA, Koki – SATO, Nobuhiro – SAKAMOTO, Ryota – TAKATANI, Kouhei – MORENO, Daniel – ŠKORŇA, Peter – SCHOLTZOVÁ, Eva – SZILAGYI, Robert** – NISHIHARA, Hirotomo**. Quantitative and qualitative analysis of nitrogen species in carbon at the ppm level. In Chem, 2024, vol. 10, no. 8, p. 2450-2463. (2023: 19.1 – IF, Q1 – JCR, 6.556 – SJR, Q1 – SJR). https://doi.org/10.1016/j.chempr.2024.03.029 Typ: ADCA

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Deep ocean creatures, such as lanternfish, rely heavily on bioluminescence to communicate with each other and their surroundings. This ability to produce light is crucial for various survival strategies, including attracting mates, luring prey, and evading predators. The light emitted can vary in time, intensity, and even colour, allowing these organisms to convey complex signals.
Recent research has explored materials that mimic this natural phenomenon by changing the colour of emitted light in response to external stimuli. This study focuses on the integration of organic dyes with 2D materials forming structures that exhibit tunable optical properties. These materials respond to changes in their environment, such as the presence of specific solvents, leading to photoluminescent alterations.
The crucial component is the naphthalene dipyridine dication, synthesized by Prof. Kawamata’s lab. This compound can form excimer species due to non-covalent π-π interactions within the confined space, particularly when triggered by the presence of DMSO. Moreover, its reversible nature renders this material as a potential candidate in applications such as optoelectronics, sensors and imaging technologies.

Publication:

• MATEJDES, Marián – ŠKORŇA, Peter – SLANÝ, Michal – KLEMENT, Róbert – BUJDÁK, Juraj – KAWAMATA, Jun – BREU, Josef. Excimer formation in a 2D confined space. In Materials Today Chemistry, 2024, vol. 42, art no. 102436. (2023: 6.7 – IF, Q1 – JCR, 1.239 – SJR, Q1 – SJR). https://doi.org/10.1016/j.mtchem.2024.102436 Typ: ADCA

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Tetraboron carbide (B₄C) is considered one of the most important ceramic materials for the defense, nuclear and engineering industries, due to its excellent combination of properties, such as extremely high hardness, refractoriness, chemical inertness, high temperature stability and low density. Difficult preparation and insufficient oxidation resistance limit the wider use of this exceptional material. For this reason, B₄C-SiC-based composites were developed in collaboration with the Vinča Institute of Nuclear Sciences in Serbia. The influence of SiC in the form of fibres (2.5 to 10 wt.%) and particles (25 – 75 wt.%) on the sinterability and high-temperature properties of B₄C-SiC materials, which were prepared at the IIC SAS in the temperature range of 1850 – 2000°C and a pressure of 70 MPa, was systematically studied. In both cases, the sinterability of the materials significantly improved with increasing SiC content. The B₄C material with 5 wt.% SiC fibres achieved the highest hardness (43 GPa) among all of the investigated composites, and only a relatively mild damage was observed after an oxy-acetylene flame treatment at the temperature of 1800°C (Fig. 1a). The materials with the addition of SiC particles also showed a relatively mild damage after laser ablation testing, where the surface temperature of the samples exceeded 10 000 K. Under these conditions, only local melting and fragmentation occurred (Fig. 1b), but the unaffected areas were free of cracks. In both works, the applicability of these materials in oxidating conditions at high temperatures was significantly improved.

Publication:

• MATOVIĆ, Branko** – MALETAŠKIĆ, Jelena – DORDEVIĆ, Marija Prekajski – TATARKO, Peter – HANZEL, Ondrej – HIČÁK, Michal – CHLUP, Zdeněk – CVIJOVIĆ-ALAGIĆ, Ivana. Fabrication of boron carbide ceramics reinforced with silicon carbide fibers. In Ceramics International, 2024, vol. 50, no. 21B, p. 42188-42194. (2023: 5.1 – IF, Q1 – JCR, 0.938 – SJR, Q1 – SJR). https://doi.org/10.1016/j.ceramint.2024.08.062 Type: ADCA
• MATOVIĆ, B.** – TATARKO, Peter – MAKSIMOVIĆ, V. – MALETAŠKIĆ, J. – STOILJKOVIĆ, M. – HANZEL, Ondrej – CVIJOVIC-ALAGIC, I. Densification of additive-free B4C-SiC composites by spark plasma sintering. In Journal of the European Ceramic Society, 2024, vol. 44, no. 9., p. 5340-5346. (2023: 5.8 – IF, Q1 – JCR, 1.198 – SJR, Q1 – SJR). ISSN 0955-2219. Dostupné na: https://doi.org/10.1016/j.jeurceramsoc.2023.12.024 Type: ADCA
• Projekty: APVV-21-0402; VEGA 2/0007/21

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Low-temperature molten salt synthesis is a relatively new procedure that has been successfully used for the preparation of YAG (Y3Al5O12) and Nd doped YAG (Nd:YAG). It is for the first time demonstrated that crystallized YAG and Nd doped YAG may be produced without the use of any alumina at temperatures as low as 630 °C (compared to 1600 °C of the solid – state conversion) utilizing only the molten cryolite (Na₃AlF₆)-yttria (Y₂O₃), reaction mixture where cryolite works as a solvent and source of Al and yttria as a solute and source of Y and O. It will be shown that the molten fluoride synthesis procedure using molten Na₃AlF₆ could be a feasible way for the synthesis of YAG and potentially other oxide materials.

Publication:

1. KORENKO, Michal** – ŠIMKO, František** – ALLIX, Mathieu – RAKHMATULLIN, Aydar – PITCHER, Michael J. – KING, Graham. Determination of the Na3AlF6–Y2O3 Phase Diagram and Its Implications for Low-Temperature YAG/Nd:YAG Synthesis. In Crystal Growth & Design, 2024, vol. 24, no. 18, pp. 7494–7503. (2023: 3.2 – IF, Q1 – JCR, 0.649 – SJR, Q2 – SJR). https://doi.org/10.1021/acs.cgd.4c00684 Typ: ADCA

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An innovative sintering strategy has been devised to produce fine-grained transparent yttrium oxide. Limited amounts of Al₂O₃ and SiO₂ (≤1 wt.%), were used as sintering additives. The composition of the liquid phase produced by the additives continually changes during sintering. Using the variations of the liquid phase composition, the densification of samples was promoted at lower temperatures, and grain growth was suppressed during the final stages of sintering. Translucent yttrium oxide was obtained after sintering at 1650°C for 2 min, a significantly lower temperature, 100-200°C, than the conventional sintering schedules, with a fine-grained microstructure immune to grain growth.

Publication:

• NAJAFZADEHKHOEE, Aliasghar – TALIMIAN, Ali** – GIRMAN, Vladimír – SEDLÁK, Richard – HVIZDOŠ, Pavol – MACA, Karel – GALUSEK, Dušan. Liquid phase sintering of yttrium oxide: The effect of Al2O3 and SiO2 additives. In Journal of the European Ceramic Society, 2024, vol. 44, p. 383-392. (2023: 5.8 – IF, Q1 – JCR, 1.198 – SJR, Q1 – SJR). https://doi.org/10.1016/j.jeurceramsoc.2023.08.055

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