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2. Mn-induced stabilization of a ▫$\beta$▫-alumina-type defect structure in barium hexaferrite nanoplateletsDarko Makovec, Matic Poberžnik, Janvit Teržan, Tomaž Mertelj, Damjan Vengust, Goran Dražić, Darja Lisjak, Sašo Gyergyek, 2026, izvirni znanstveni članek Povzetek: Hexaferrite nanoplatelets exhibit size-dependent structural variations influencing their magnetic properties. Here, we synthesized Mn-substituted barium ferrite nanoplatelets via hydrothermal methods, achieving up to ∼27% Fe substitution. Advanced STEM and Raman analyses revealed depletion of Fe(2b) trigonal lattice sites and associated oxygen vacancies, forming a β-alumina-type ferrite structure─representing the first pure Ba2+ β-ferrite analogue. First-principles modeling confirmed the thermodynamic stabilization of this defected structure at higher Mn/Fe ratios. Mn substitution reduced nanoplatelet size and suppressed magnetic properties, which were restored upon annealing at 800 °C, reverting to the M-type hexaferrite structure with expected magnetic behavior. These findings elucidate nanoscale structural adaptations induced by chemical substitution and offer insights into tailoring the magnetic properties of barium ferrite nanoplatelets through controlled synthesis and post-treatment.
Objavljeno v DiRROS: 23.03.2026; Ogledov: 123; Prenosov: 94
 Celotno besedilo (11,07 MB)
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3. Nonconductive ferrofluids from permanently magnetic nanoplatelets hybridized with polar phosphonic ligandsAli Tufani, Nina Popov, Janez Kovač, Stanislav Čampelj, Andraž Mavrič, Tomas Landovsky, Martin Cigl, Petra Vaňkátová, Martin Loula, Vladimíra Novotná, Matic Poberžnik, Gabriela Herrero-Saboya, Layla Martin-Samos, Alenka Mertelj, Darja Lisjak, 2025, izvirni znanstveni članek Povzetek: Ferrofluids composed of permanently magnetic nanoplatelets of barium hexaferrite (BHF NPLs) represent a remarkable class of materials that can form a ferromagnetic liquid state at sufficiently high concentrations. To date, the surfactant dodecylbenzenesulfonic acid (DBSA) has demonstrated an excellent colloidal stability of the BHF NPLs in alcohols. However, a key limitation of DBSA is its labile adsorption onto the NPLs, meaning that the surface coverage by surfactant molecules is highly sensitive to various factors. In this study, we demonstrate that polar ligands based on phosphonic acids and phosphonate esters offer a viable alternative to DBSA, providing enhanced robustness and colloidal stability in low-polar solvents. Phosphonic ligands with the different electron-withdrawing groups and alkyl chain lengths of the terminal chain and linker were synthesized. Their attachment to the surface of the BHF NPLs was studied for various conditions and followed by a combination of spectroscopic techniques, thermogravimetry, and electrokinetic measurements. The results confirmed the theoretically predicted surface condensation of the ligands onto the BHF NPLs surfaces at 120 °C in 1-hexanol, whereas at lower temperatures or in more polar solvents the ligands were mostly physisorbed. The NPL hybrids with chemisorbed ligands having surface densities of at least 0.4 molecules per nm2 formed stable ferrofluids in 1-hexanol. Due to the relatively low polarity of 1-hexanol, the ligands remain protonated and the ferrofluids have negligible electric conductivity and are suitable for the development of novel magneto-optic sensors that can operate under an electric field.
Objavljeno v DiRROS: 21.05.2025; Ogledov: 962; Prenosov: 271
Celotno besedilo (2,29 MB) |
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6. Editors' choise - The effect of anchor group and alkyl backbone chain on performance of organic compounds as corrosion inhibitors for aluminum investigated using an Integrative experimental-modeling approachIngrid Milošev, Dolores Zimerl, Charly Carrière, Sandrine Zanna, Antoine Seyeux, Jernej Iskra, Stojan Stavber, Fatah Chiter, Matic Poberžnik, Dominique Costa, Anton Kokalj, Philippe Marcus, 2020, izvirni znanstveni članek Objavljeno v DiRROS: 14.05.2025; Ogledov: 829; Prenosov: 252
Celotno besedilo (5,21 MB) |
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9. DFT study of ▫$\mathrm{Cl^-}$▫ ingress into organic self-assembled monolayers on aluminumFatah Chiter, Dominique Costa, Matic Poberžnik, Ingrid Milošev, Philippe Marcus, Anton Kokalj, 2023, izvirni znanstveni članek Povzetek: We address the mechanism by which organic layers on aluminum substrate hinder the penetration of Cl− toward the metal substrate. Localized corrosion by chlorides on Al and its alloys is a major problem, and organic molecules that form self-assembled monolayers on metal substrates may provide efficient corrosion protection. In one of our previous works, we established experimentally that long-chain n-alkyl carboxylic acids form protective layers against Cl− corrosion on Al substrates. In a different work, we identified, using implicit models of the organic layer and metal substrate, two essential effects by which organic layers hinder the penetration of Cl− ions toward the metal substrate. The first effect is due to the inferior solvation of ions in the organic layer compared to that in an aqueous solvent. The second effect is due to the electric field at the electrochemical interface, and the extent to which it affects the penetration of Cl− depends on the electrode potential and the thickness of the organic layer. Both effects are related to a low dielectric constant of the self-assembled monolayer. In the present study, we continue our investigation and explicitly model the organic monolayer and Al substrate using density-functional-theory calculations. To this end, we consider organic monolayers consisting of either dodecanoic- or hexanoic-acid molecules. Current calculations confirm the findings of the simplified implicit models, i.e. the energy barrier for the Cl− penetration increases with the thickness of the organic monolayer and with Cl− concentration in the monolayer. Furthermore, we propose a new mechanism by which Cl− penetrates the organic monolayer. Due to the considerably inferior solvation of Cl− in the organic layer compared to that in water, calculations suggest that it is energetically easier to locally “open” the organic monolayer by creating a hole large enough to accommodate water molecules and Cl−. The presence of water molecules ensures a stronger Cl− solvation and a better electrostatic screening between anions. While the energy barrier for the Cl− penetration via the local “opening” mechanism is suggested to be smaller than for the penetration of Cl− into dense homogeneous organic monolayer, it is still significant enough to pose a considerable kinetic barrier for the penetration of Cl− from the aqueous solution into the organic monolayer at room temperature.
Ključne besede: aluminium, chlorides, self-assembled monolayer, localized corrosion, density-functional theory
Objavljeno v DiRROS: 29.04.2025; Ogledov: 1057; Prenosov: 456
Celotno besedilo (2,33 MB)
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10. Atypical adsorption of hydrogen on native ultrathin aluminum oxide filmsMatic Poberžnik, Anton Kokalj, 2025, izvirni znanstveni članek Povzetek: We report on an unusual hydrogen adsorption mode on native ultrathin aluminum-oxide films. Based on systematic density-functional theory (DFT) calculations on a model oxide film of varying thickness—i.e., α–Al2O3(001) supported on Al(111)—we show that on ultrathin films, H preferentially adsorbs on surface Al ions instead of O ions, as one would expect from chemical intuition. The so-adsorbed H is in hydride form, and for ultrathin films, it gets the electron charge from Al atoms at the oxide/metal interface. In contrast, for thicker films, this electron transfer ceases, and the charge instead predominantly comes from the surface O ions, making H adsorbed at Al sites inferior to H adsorbed at O sites. We further show that H adsorbed at Al sites can lead to H2 formation, which we propose to be connected to the experimentally observed hydrogen evolution in pits formed during the pitting corrosion of aluminum, where the protective oxide film has considerably degraded and is very thin
Objavljeno v DiRROS: 15.04.2025; Ogledov: 784; Prenosov: 194
Celotno besedilo (2,54 MB) |
