104 results on '"Milan Dopita"'
Search Results
2. Capability of X-ray diffraction for the study of microstructure of metastable thin films
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David Rafaja, Christina Wüstefeld, Milan Dopita, Mykhaylo Motylenko, and Carsten Baehtz
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metastable thin films ,microstructure ,X-ray diffraction ,Crystallography ,QD901-999 - Abstract
Metastable phases are often used to design materials with outstanding properties, which cannot be achieved with thermodynamically stable compounds. In many cases, the metastable phases are employed as precursors for controlled formation of nanocomposites. This contribution shows how the microstructure of crystalline metastable phases and the formation of nanocomposites can be concluded from X-ray diffraction experiments by taking advantage of the high sensitivity of X-ray diffraction to macroscopic and microscopic lattice deformations and to the dependence of the lattice deformations on the crystallographic direction. The lattice deformations were determined from the positions and from the widths of the diffraction lines, the dependence of the lattice deformations on the crystallographic direction from the anisotropy of the line shift and the line broadening. As an example of the metastable system, the supersaturated solid solution of titanium nitride and aluminium nitride was investigated, which was prepared in the form of thin films by using cathodic arc evaporation of titanium and aluminium in a nitrogen atmosphere. The microstructure of the (Ti,Al)N samples under study was tailored by modifying the [Al]/[Ti] ratio in the thin films and the surface mobility of the deposited species.
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- 2014
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3. Mössbauer Spectroscopy of Triphylite (LiFePO4) at Low Temperatures
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Tomáš Kmječ, Jaroslav Kohout, Milan Dopita, Miroslav Veverka, and Jan Kuriplach
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lifepo4 ,mössbauer spectroscopy ,antiferromagnetic order ,density functional theory ,Physics ,QC1-999 - Abstract
Low temperature magnetic ordering in the LiFePO 4 compound is investigated experimentally using Mössbauer spectroscopy and theoretically via first principles calculations. The evaluation of experiment carried out on a powder sample is compatible with an antiferromagnetic order of Fe ion magnetic moments. When an external magnetic field is applied, Fe magnetic moments start to deviate slightly from the [010] easy magnetization direction. These findings are confirmed by means of first principles calculations, which also suggest the magnitude of single ion magnetic anisotropy and orbital and spin-dipolar contributions to the magnetic hyperfine field, which is eventually in a good agreement with the experiment. Diffraction and magnetic measurements complement the study.
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- 2019
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4. Investigation of Nanostructures with X-ray Scattering Techniques
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Dominik Kriegner and Milan Dopita
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organic films ,magnetic thin films ,nanowires ,scanning x-ray diffraction ,anomalous x-ray diffraction ,nanoparticles ,quantum dots ,grazing incidence small angle x-ray scattering ,x-ray beam induced current ,Crystallography ,QD901-999 - Abstract
n/a
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- 2019
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5. Magnetron-Sputtered Niobium Nanoparticles for Molecular Imaging of Brain Tissues through Surface-Assisted Laser Desorption/Ionization Mass Spectrometry
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Pavel Pleskunov, Vadym Prysiazhnyi, Daniil Nikitin, Tereza Košutová, Miroslav Cieslar, Ivan Gordeev, Zdeněk Krtouš, Suren Ali-Ogly, Ján Šomvársky, Mariia Protsak, Kateryna Biliak, Ksenia Kishenina, Antonín Bednařík, Milan Dopita, Jan Preisler, and Andrei Choukourov
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General Materials Science - Published
- 2022
6. Sputtered Ir–Ru based catalysts for oxygen evolution reaction: Study of iridium effect on stability
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Tomáš Hrbek, Peter Kúš, Tereza Košutová, Kateřina Veltruská, Thu Ngan Dinhová, Milan Dopita, Vladimír Matolín, and Iva Matolínová
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Fuel Technology ,Renewable Energy, Sustainability and the Environment ,Energy Engineering and Power Technology ,Condensed Matter Physics - Published
- 2022
7. Antibacterial studies of ZnO and silica capped manganese doped zinc sulphide nanostructures
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Sunil Kumar, Anita Jain, Sanjay Panwar, Indu Sharma, Suhaas Gupta, Milan Dopita, and Ravi Kant Choubey
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General Materials Science ,General Chemistry - Published
- 2023
8. Photothermal properties of aluminum oxide/Ag nanoparticles cermet-based coating synthesized by reactive magnetron co-sputtering
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Adrien Chauvin, Grégory Savorianakis, Lukas Horak, Milan Dopita, Michel Voué, Stephanos Konstantinidis, François Reniers, and Rony Snyders
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Materials Chemistry ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films - Published
- 2023
9. The Impact of Pt-Ir Nanoparticle Catalyst Structure on Oxygen Evolution and Reduction Activity
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Lucinda Blanco-Redondo, Yevheniia Lobko, Kateřina Veltruská, Jaroslava Nováková, Michal Mazur, Tomáš Hrbek, Milan Dopita, Iva Matolínová, and Vladimír Matolín
- Published
- 2023
10. Optimal Pt-Au Alloying for Efficient and Stable Oxygen Reduction Reaction Catalysts
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Xianxian Xie, Valentín Briega-Martos, Riccardo Farris, Milan Dopita, Mykhailo Vorokhta, Tomáš Skála, Iva Matolínová, Konstantin M. Neyman, Serhiy Cherevko, and Ivan Khalakhan
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General Materials Science - Abstract
Stabilization of cathode catalysts in hydrogen-fueled proton-exchange membrane fuel cells (PEMFCs) is paramount to their widespread commercialization. Targeting that aim, Pt-Au alloy catalysts with various compositions (Pt
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- 2022
11. Insights into the growth of nanoparticles in liquid polyol by thermal annealing
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Anastasiya P. Sergievskaya, Cinthia Antunes Corrêa, Milan Dopita, Anna Fucikova, David Cornil, Stephanos Konstantinidis, Adrien Chauvin, J. Vesely, and Jérôme Cornil
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Copper oxide ,Materials science ,Annealing (metallurgy) ,Nanoparticle ,chemistry.chemical_element ,Bioengineering ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Pentaerythritol ,Metal ,chemistry.chemical_compound ,Polyol ,Sputtering ,General Materials Science ,chemistry.chemical_classification ,General Engineering ,General Chemistry ,021001 nanoscience & nanotechnology ,Copper ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,chemistry ,Chemical engineering ,visual_art ,visual_art.visual_art_medium ,0210 nano-technology - Abstract
We report on the growth of metal- and metal-oxide based nanoparticles (NPs) in heated polyol solutions. For this purpose, NPs are produced by the sputtering of a silver, gold, or a copper target to produce either silver, gold, or copper oxide NPs in pentaerythritol ethoxylate (PEEL) which has been annealed up to 200 °C. The objective of the annealing step is the fine modulation of their size. Thus, the evolution of the NP size and shape after thermal annealing is explained according to collision/coalescence kinetics and the affinity between the metal-/metal-oxide and PEEL molecule. Moreover, highlights of few phenomena arising from the annealing step are described such as (i) the reduction of copper oxide into copper by the polyol process and (ii) the effective formation of carbon dots after annealing at 200 °C.
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- 2021
12. The Effect of Annealing Temperature on Antiferroelectric Zirconia
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Anthony A. Gaskell, Zheng Wang, Milan Dopita, Dominik Kriegner, Nujhat Tasneem, and Asif I. Khan
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- 2022
13. Evolution of the PtNi Bimetallic Alloy Fuel Cell Catalyst under Simulated Operational Conditions
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Daniel J. S. Sandbeck, Milan Dopita, Marco Bogar, Ivan Khalakhan, Yurii Yakovlev, Mykhailo Vorokhta, Heinz Amenitsch, Serhiy Cherevko, Peter Kúš, and Iva Matolínová
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Ostwald ripening ,Materials science ,Alloy ,02 engineering and technology ,Electrolyte ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Corrosion ,Catalysis ,symbols.namesake ,Chemical engineering ,engineering ,symbols ,General Materials Science ,Thin film ,0210 nano-technology ,Bimetallic strip - Abstract
Comprehensive understanding of the catalyst corrosion dynamics is a prerequisite for the development of an efficient cathode catalyst in proton-exchange membrane fuel cells. To reach this aim, the behavior of fuel cell catalysts must be investigated directly under reaction conditions. Herein, we applied a strategic combination of in situ/online techniques: in situ electrochemical atomic force microscopy, in situ grazing incidence small angle X-ray scattering, and electrochemical scanning flow cell with online detection by inductively coupled plasma mass spectrometry. This combination of techniques allows in-depth investigation of the potential-dependent surface restructuring of a PtNi model thin film catalyst during potentiodynamic cycling in an aqueous acidic electrolyte. The study reveals a clear correlation between the upper potential limit and structural behavior of the PtNi catalyst, namely, its dealloying and coarsening. The results show that at 0.6 and 1.0 VRHE upper potentials, the PtNi catalyst essentially preserves its structure during the entire cycling procedure. The crucial changes in the morphology of PtNi layers are found to occur at 1.3 and 1.5 VRHE cycling potentials. Strong dealloying at the early stage of cycling is substituted with strong coarsening of catalyst particles at the later stage. The coarsening at the later stage of cycling is assigned to the electrochemical Ostwald ripening process.
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- 2020
14. Synthesis and Physical Properties of Uranium Thin-Film Hydrides Uh2 and Β-Uh3
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Evgenia Tereshina-Chitrova, Ladislav Havela, Mykhaylo Paukov, Oleksandra Koloskova, Lukas Horak, Milan Dopita, Mayerling Martinez, Miroslav Cieslar, Zbynek Šoban, Thomas Gouder, and Frank Huber
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- 2022
15. Synthesis and physical properties of uranium thin-film hydrides UH2 and \b{eta}-UH3
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Evgenia A. Tereshina-Chitrova, Ladislav Havela, Mykhaylo Paukov, Oleksandra Koloskova, Lukáš Horák, Milan Dopita, Mayerling Martinez Celis, Miroslav Cieslar, Zbyněk Šobáň, Thomas Gouder, and Frank Huber
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Condensed Matter - Materials Science ,Materials Chemistry ,Metals and Alloys ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Surfaces and Interfaces ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
Formation of thin uranium hydrides films, UH2 and \b{eta}-UH3, synthesized by a reactive dc sputtering of uranium metal, was explored using variable deposition conditions. Obtained stable oxygen-free hydride films were studied by a variety of methods, both in situ (photoelectron spectroscopy - XPS), and ex-situ (x-ray diffraction - XRD, transmission electron microscopy - TEM), electrical resistivity, and magnetometry). Both types of hydrides are ferromagnetic, the Curie temperatures of UH2 and \b{eta}-UH3 are approx. 120 and 170 K, respectively. Ferromagnetism in the thin films is robust and does not depend on structure details while electrical resistivity data reflect disorder in both types of hydrides.
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- 2022
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16. Unraveling the Surface Chemistry and Structure in Highly Active Sputtered Pt3Y Catalyst Films for the Oxygen Reduction Reaction
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Milan Dopita, Tomáš Skála, Rosemary Brown, Konstantin M. Neyman, Ivan Khalakhan, Thomas Vonderach, Iva Matolínová, Henrik Grönbeck, Niklas Lindahl, Vladimír Matolín, Mykhailo Vorokhta, and Björn Wickman
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Materials science ,Oxide ,chemistry.chemical_element ,Proton exchange membrane fuel cell ,02 engineering and technology ,Yttrium ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Overlayer ,Catalysis ,chemistry.chemical_compound ,chemistry ,X-ray photoelectron spectroscopy ,Chemical engineering ,General Materials Science ,Thin film ,0210 nano-technology ,Platinum - Abstract
Platinum is the most widely used and best performing sole element for catalyzing the oxygen reduction reaction (ORR) in low-temperature fuel cells. Although recyclable, there is a need to reduce the amount used in current fuel cells for their extensive uptake in society. Alloying platinum with rare-earth elements such as yttrium can provide an increase in activity of more than seven times, reducing the amount of platinum and the total amount of catalyst material required for the ORR. As yttrium is easily oxidized, exposure of the Pt-Y catalyst layer to air causes the formation of an oxide layer that can be removed during acid treatment, leaving behind a highly active pure platinum overlayer. This paper presents an investigation of the overlayer composition and quality of Pt3Y films sputtered from an alloy target. The Pt3Y catalyst surface is investigated using synchrotron radiation X-ray photoelectron spectroscopy before and after acid treatment. A new substoichiometric oxide component is identified. The oxide layer extends into the alloy surface, and although it is not completely removed with acid treatment, the catalyst still achieves the expected high ORR activity. Other surface-sensitive techniques show that the sputtered films are smooth and bulk X-ray diffraction reveals many defects and high microstrain. Nevertheless, sputtered Pt3Y exhibits a very high activity regardless of the film's oxide content and imperfections, highlighting Pt3Y as a promising catalyst. The obtained results will help to support its integration into fuel cell systems.
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- 2019
17. Influence of thermal treatment on the structure and electrical conductivity of thermally expanded graphite
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Alina Madalina Darabut, Yevheniia Lobko, Yurii Yakovlev, Miquel Gamón Rodríguez, Kateřina Veltruská, Břetislav Šmíd, Peter Kúš, Jaroslava Nováková, Milan Dopita, Maryna Vorokhta, Vladimír Kopecký, Marek Procházka, Iva Matolínová, and Vladimír Matolín
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Mechanics of Materials ,General Chemical Engineering - Published
- 2022
18. Cerium Oxalate Morphotypes: Synthesis and Conversion into Nanocrystalline Oxide
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Petr Brázda, Milan Dopita, Pavlina Markova, Mirko Antonio Vacca, and Vaclav Tyrpekl
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Precipitation (chemistry) ,Oxalic acid ,Oxide ,chemistry.chemical_element ,Nanocrystalline material ,law.invention ,Inorganic Chemistry ,Grain growth ,chemistry.chemical_compound ,Cerium ,chemistry ,Chemical engineering ,law ,Calcination ,Physical and Theoretical Chemistry ,Cerium oxalate - Abstract
Cerium dioxide is a scientifically and technologically important material with a wide range of potential applications, particularly in solid oxide fuel cells and catalysis. Herein, we report a study focusing on the synthesis of nanocrystalline cerium dioxide via thermal decomposition of the oxalate salt. Simply by changing reaction conditions (temperature, concentration, acidity, strike) during the precipitation of the cerium solution with oxalic acid, we were able to obtain different morphologies. The main reaction parameters were mapped and linked to the morphology of the final products. Additionally, it was proved that oxalate precipitation is a robust reaction proceeding at relatively extreme contitions. Moreover, the conversion of cerium oxalate to nanocrystalline oxide was followed to monitor the progress of the reaction, the texture evolution, and the grain growth. The results showed that, for unvaried heating cycle, the grain size of converted material is linked to morphology. The thinner was the original microcrystal the smaller were the CeO2 nanocrystals after calcination. In addition, the grains were found smaller near the edges of the ex-oxalate microcrystals. In both cases, this behavior results from asymmetrical limitations of diffusion during grain growth.
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- 2019
19. Lattice defects in severely deformed biomedical Ti-6Al-7Nb alloy and thermal stability of its ultra-fine grained microstructure
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Jakub Čížek, Veronika Polyakova, Irina P. Semenova, Kristína Bartha, Milan Dopita, Josef Stráský, Pavel Zháňal, Michal Hájek, František Lukáč, Miloš Janeček, and Petr Harcuba
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Materials science ,Scanning electron microscope ,Mechanical Engineering ,Alloy ,Metals and Alloys ,Recrystallization (metallurgy) ,02 engineering and technology ,Thermal treatment ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,0104 chemical sciences ,Positron annihilation spectroscopy ,Solid solution strengthening ,Mechanics of Materials ,Vacancy defect ,Materials Chemistry ,engineering ,Composite material ,0210 nano-technology - Abstract
Biomedical Ti-6Al-7Nb alloy was prepared by a dedicated thermal treatment followed by equal-channel angular pressing (ECAP) and extrusion. Ultra-fine grained duplex microstructure consisting of deformed primary α-grains and fragmented α + β region was achieved. Microstructural changes during heating with the rate of 5 °C/min were studied by in-situ electrical resistance. Microstructure after deformation and also after subsequent heating was thoroughly characterized by scanning electron microscopy, X-ray diffraction, and positron annihilation spectroscopy (PAS). X-ray diffraction and positron annihilation spectroscopy proved a very high dislocation density and the presence of high concentration of vacancy clusters in deformed material. The ultra-fine grained microstructure of Ti-6Al-7Nb alloy is stable up to 440 °C, while upon heating to 550 °C and to 660 °C, the dislocation density decreases and vacancy clusters disappear. Enhanced microhardness can be achieved by ECAP followed by aging at 500 °C. Upon heating to 660 °C, the microhardness decreases due to ongoing recovery and recrystallization. Coincidence Doppler broadening (CDB), a special method of PAS, proved that dislocation cores are preferentially occupied by Al atoms that are known to cause substitutional solid solution strengthening.
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- 2019
20. Spin fluctuations in hydrogen-stabilized Laves phase UTi2H5
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Ladislav Havela, Petr Doležal, Oleksandra Koloskova, Milan Dopita, M. Paukov, Peter Minárik, Daria Drozdenko, Michał Falkowski, Silvie Mašková, and V. Buturlim
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010302 applied physics ,Magnetization dynamics ,Materials science ,Hydrogen ,Condensed matter physics ,chemistry.chemical_element ,Field dependence ,02 engineering and technology ,Laves phase ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Magnetic susceptibility ,chemistry ,Electrical resistivity and conductivity ,Seebeck coefficient ,Lattice (order) ,0103 physical sciences ,0210 nano-technology - Abstract
Uranium Laves phase UTi2 does not exist in a pure form, but can be stabilised by the presence of hydrogen, which can be absorbed in concentration exceeding 5 H atoms/f.u. Low temperature specific heat, magnetic susceptibility, and resistivity indicate that UTi2H5 is a spin fluctuator close to the verge of magnetic ordering. Its susceptibility follows at high temperatures the Curie–Weiss law with U effective moment µeff[ = 3.1 µB/U and paramagnetic Curie temperature Θp = −200 K. The temperature dependence of specific heat exhibits a pronounced and weakly field dependent upturn in Cp/T versus T below 10 K reflecting the effect of spin fluctuations. It can be described by an additional T½ term. The Sommerfeld coefficient γ = 256 mJ/mol K2 classifies the compound as a mid-weight heavy fermion. Spin fluctuations are affecting also electrical and thermal transport and thermoelectric power, which all resemble UAl2. A lattice anomaly at ≈ 240 K, attributed to the melting of hydrogen sublattice, refl...
- Published
- 2019
21. 57Fe-enriched perovskites M(Fe0.5Nb0.5)O3 (M – Pb, Ba) studied by Mössbauer spectroscopy, NMR and XRD in the wide temperature range 4.2–533 K
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Milan Dopita, J. Bednarcik, J. Plocek, Denisa Kubániová, V. Chlan, Martin Cesnek, Miroslav Maryško, Tomáš Kmječ, Jaroslav Kohout, K. Zaveta, and M. Adamec
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010302 applied physics ,Materials science ,Transition temperature ,Analytical chemistry ,02 engineering and technology ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,0103 physical sciences ,Mössbauer spectroscopy ,Antiferromagnetism ,Multiferroics ,0210 nano-technology ,Hyperfine structure ,Powder diffraction - Abstract
The 57Fe enriched almost single-phase perovskites Pb(Fe0.5Nb0.5)O3 (PFN) and Ba(Fe0.5Nb0.5)O3 (BFN), prepared by a ceramic method (solid-state synthesis), were studied by Mossbauer spectroscopy, nuclear magnetic resonance (NMR), conventional and synchrotron X-ray powder diffraction (XRD). The temperature dependences of hyperfine and structural parameters of PFN, BFN from 4.2 K to temperatures above ferroelectric ordering of PFN (TS ∼ 375 K), with attention to the values of magnetic and structural transitions, were obtained. The antiferromagnetic magnetic ordering transitions were found under the Neel temperatures TN ∼ 167(3) K and 32(2) K for PFN and BFN, respectively. The spin-glass transition was at TG ∼ 10(3) K and 20(5) K for PFN and BFN, respectively. In PFN sample a small change of structural parameters around TN and structural change from trigonal to cubic structure at T ∼ 400 K was observed by XRD. The temperature dependence of XRD shows stable cubic structure in the temperature range from 4.2 K to 530 K for BFN. From Mossbauer and NMR spectroscopies it is found that both structures have perturbed environments for Nb and Fe. However, in case of PFN the low values of transferred hyperfine fields disfavour random Fe/Nb arrangement and allow proposing a picture of Fe/Nb arrangement.
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- 2019
22. Rapid floating zone growth of Ni2MnGa single crystals exhibiting magnetic shape memory functionality
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Václav Holý, Petr Cejpek, R. H. Colman, Milan Dopita, Oleg Heczko, Ladislav Straka, and Martin Veis
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Diffraction ,Materials science ,Single crystal growth ,Mechanical Engineering ,Metals and Alloys ,Analytical chemistry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Magnetization ,Reference sample ,Magnetic shape-memory alloy ,Mechanics of Materials ,Homogeneity (physics) ,Materials Chemistry ,0210 nano-technology ,human activities ,Single crystal ,Directional solidification - Abstract
To obtain a material exhibiting magnetically induced reorientation (MIR), one of the magnetic shape memory effects, a well-developed method for single crystal growth is crucial. A [ 100 ] oriented Ni2MnGa single crystal exhibiting MIR was successfully prepared using the floating-zone technique with a high speed of 80 mm/h. The comparison with a sample grown by Bridgman method and a reference sample grown in AdaptaMat Ltd. by directional solidification is provided based on elemental homogeneity, crystallographic quality by x-ray diffraction, transformation behaviour and magnetic properties. All these methods indicated that the single crystal grown by floating zone with high speed is comparable or superior to the samples prepared by other methods. Importantly, the magnetization measurement revealed that the single crystal prepared this way exhibits MIR down to 10 K.
- Published
- 2019
23. From positive to colossal negative thermal expansion in a novel family of bimetallic imidazolates
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Sanja Burazer, Lukáš Horák, Yaroslav Filinchuk, Milan Dopita, Radovan Černý, and Jasminka Popović
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Inorganic Chemistry ,Structural Biology ,General Materials Science ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Biochemistry - Published
- 2021
24. Antiferroelectric negative capacitance from a structural phase transition in zirconia
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Michael Hoffmann, Zheng Wang, Nujhat Tasneem, Ahmad Zubair, Prasanna Venkatesan Ravindran, Mengkun Tian, Anthony Arthur Gaskell, Dina Triyoso, Steven Consiglio, Kandabara Tapily, Robert Clark, Jae Hur, Sai Surya Kiran Pentapati, Sung Kyu Lim, Milan Dopita, Shimeng Yu, Winston Chern, Josh Kacher, Sebastian E. Reyes-Lillo, Dimitri Antoniadis, Jayakanth Ravichandran, Stefan Slesazeck, Thomas Mikolajick, and Asif Islam Khan
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Condensed Matter - Materials Science ,Condensed Matter::Materials Science ,Multidisciplinary ,Affordable and Clean Energy ,General Physics and Astronomy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Chemistry ,Physics - Applied Physics ,Applied Physics (physics.app-ph) ,General Biochemistry, Genetics and Molecular Biology - Abstract
Crystalline materials with broken inversion symmetry can exhibit a spontaneous electric polarization, which originates from a microscopic electric dipole moment. Long-range polar or anti-polar order of such permanent dipoles gives rise to ferroelectricity or antiferroelectricity, respectively. However, the recently discovered antiferroelectrics of fluorite structure (HfO2 and ZrO2) are different: A non-polar phase transforms into a polar phase by spontaneous inversion symmetry breaking upon the application of an electric field. Here, we show that this structural transition in antiferroelectric ZrO2 gives rise to a negative capacitance, which is promising for overcoming the fundamental limits of energy efficiency in electronics. Our findings provide insight into the thermodynamically forbidden region of the antiferroelectric transition in ZrO2 and extend the concept of negative capacitance beyond ferroelectricity. This shows that negative capacitance is a more general phenomenon than previously thought and can be expected in a much broader range of materials exhibiting structural phase transitions.
- Published
- 2021
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25. Co-sputtering of gold and copper onto liquids: a route towards the production of porous gold nanoparticles
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Stephanos Konstantinidis, Abdel-Aziz El Mel, Milan Dopita, Jérôme Cornil, Cinthia Antunes Corrêa, Adrien Chauvin, David Cornil, Pierre-Yves Tessier, Anna Fucikova, Elen Duverger-Nédellec, Anastasiya P. Sergievskaya, J. Vesely, Charles University [Prague] (CU), Centre d'Innovation et de Recherche en Matériaux Polymères (CIRMAP), Université de Mons (UMons), Institut des Matériaux Jean Rouxel (IMN), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Ecole Polytechnique de l'Université de Nantes (EPUN), Université de Nantes (UN)-Université de Nantes (UN), Institute of Physics of the Czech Academy of Sciences (FZU / CAS), Czech Academy of Sciences [Prague] (CAS), and University of Mons [Belgium] (UMONS)
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Copper oxide ,Materials science ,Annealing (metallurgy) ,Alloy ,Nanoparticle ,chemistry.chemical_element ,Bioengineering ,02 engineering and technology ,engineering.material ,010402 general chemistry ,01 natural sciences ,chemistry.chemical_compound ,Sputtering ,General Materials Science ,Electrical and Electronic Engineering ,ComputingMilieux_MISCELLANEOUS ,Nanoporous ,Mechanical Engineering ,General Chemistry ,021001 nanoscience & nanotechnology ,Copper ,0104 chemical sciences ,chemistry ,Chemical engineering ,Mechanics of Materials ,Colloidal gold ,engineering ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,0210 nano-technology - Abstract
Effective methods for the synthesis of high-purity nanoparticles (NPs) have been extensively studied for a few decades. Among others, cold plasma-based sputtering metals onto a liquid substrate appears to be a very promising technique for the synthesis of high-purity NPs. The process enables the production of very small NPs without using any toxic reagents and complex chemical synthesis routes, and enables the synthesis of alloy NPs which can be the first step towards the formation of porous NPs. In this paper, the synthesis of gold-copper alloy NPs has been performed by co-sputtering gold and copper targets over pentaerythritol ethoxylate. The resulting solutions contain a mixture of gold, copper oxide, and alloy NPs having a radius of few angstroms. The annealing of these NPs, inside the solution, has been performed in order to increase their size and further induce the dealloying of the Au-Cu NPs. The resulting NPs exhibit either a nanoporous structure or are self-organized in an agglomerate of small NPs.
- Published
- 2020
26. Core@shell nanoparticles by inflight controlled coating
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Amir Mohammad Ahadi, Hana Libenská, Tereza Košutová, Miroslav Cieslar, Veronika Červenková, Dejan Prokop, Milan Dopita, Hynek Biederman, and Jan Hanuš
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Acoustics and Ultrasonics ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
Controlled synthesis of core@shell nanoparticles (NPs) for certain applications is a difficult challenge in many nanotechnology projects. In this report, a conventional arrangement composed of a gas aggregation source (GAS) is employed to generate the core NPs, which are subsequently coated by the shell materials in a secondary planar magnetron sputtering. The important difference to the usual system is the application of the two opposing planar magnetrons in a closed field configuration. The prepared core Ag NPs by a GAS are coated/treated by the two magnetrons with Ti targets. Our findings clearly show that the shell thickness can be controlled by tuning the power delivered to the secondary magnetron plasma. Characterizations of the prepared films, by x-ray diffraction technique, disclose multi-crystalline cores covered by amorphous shells. Based on x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy measurements, different chemistry on the NPs surfaces and volume of the NPs can be achieved by tuning the operation conditions. Furthermore, the thermal annealing process leads to the growth of the crystallite size which results in emerging some microparticles caused by accelerating Ag surface mobility. The employed technique promises a reliable route to synthesize different heterogeneous NPs with stoichiometry tunable in a wide range for multi-functional devices.
- Published
- 2022
27. Thermally-driven morphogenesis of niobium nanoparticles as witnessed by in-situ x-ray scattering
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Peter Kúš, Sanja Burazer, Jan Hanuš, Andrei Choukourov, Milan Dopita, Tereza Košutová, Pavel Pleskunov, Ivan Gordeev, Lukáš Horák, Daniil Nikitin, and Miroslav Cieslar
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Materials science ,Annealing (metallurgy) ,Niobium ,chemistry.chemical_element ,Nanoparticle ,Atmospheric temperature range ,Sputter deposition ,Condensed Matter Physics ,Amorphous solid ,chemistry ,Chemical engineering ,Phase (matter) ,Niobium nanoparticles ,Small angle x-ray scattering ,In-situ x-ray diffraction ,Niobium pentoxide ,Thermal evolution ,General Materials Science ,Crystallite - Abstract
Highly porous structures consisting of niobium nanoparticles (Nb NPs) are prepared using magnetron sputtering and inert gas aggregation method. Alongside the thermally-driven evolution of nanoparticle morphology, the microstructural genesis is probed in-situ by x-ray diffraction for the temperature range up to 800 °C. The as-deposited Nb NPs are formed by the Nb core and NbOx shell. The elevated temperature triggers the gradual oxidation that proceeds until 200 °C. Above this point the structure is fully amorphous. Further increase of the temperature to 450 °C leads to a transition to the crystalline TT-Nb2O5 phase, which hexagonal structure was solved in the current study. The subsequent rise of the temperature to 600 °C results in the conversion to the orthorhombic T-Nb2O5 phase. Up to this state, the size of nanoparticles corresponds to the size of crystallites. The annealing above 600 °C causes coalescence of NPs with the formation of hundreds-of-nanometers large structures.
- Published
- 2022
28. Effect of the substrate temperature during gold-copper alloys thin film deposition by magnetron co-sputtering on the dealloying process
- Author
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Adrien Chauvin, Lukáš Horák, Pierre-Yves Tessier, Elen Duverger-Nédellec, Abdel-Aziz El Mel, Milan Dopita, Charles University [Prague] (CU), Institut des Matériaux Jean Rouxel (IMN), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Ecole Polytechnique de l'Université de Nantes (EPUN), and Université de Nantes (UN)-Université de Nantes (UN)
- Subjects
Materials science ,Nanoporous ,Scanning electron microscope ,Nanotechnology ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Sputtering ,Residual stress ,Cavity magnetron ,Materials Chemistry ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,Deposition (phase transition) ,Thin film ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS - Abstract
Nanoporous gold is of great interest for many applications due to its three dimensional interconnected porosity at nanoscale. Among all currently use techniques to obtain nanoporous gold, dealloying is one of the most used method to create a well-controlled nanoporous morphology. Only few studies report on the creation of nanoporous gold from alloy thin film deposited by magnetron co-sputtering. However, this deposition technique allows easy tune of the morphology at nanoscale. In this paper, we report on the creation of different morphologies of nanoporous gold obtained after dealloying in nitric acid of Au-Cu thin film deposited by magnetron co-sputtering. The influence of the substrate temperature during film deposition is studied by means of scanning electron microscopy and X-ray scattering analysis. We demonstrate the impact of the as-grown thin film morphology on the final nanoporous structure. We further explain the relationship between the different nanoporous morphologies and the residual stress on the as-grown thin film.
- Published
- 2020
29. Unraveling the Surface Chemistry and Structure in Highly Active Sputtered Pt
- Author
-
Rosemary, Brown, Mykhailo, Vorokhta, Ivan, Khalakhan, Milan, Dopita, Thomas, Vonderach, Tomáš, Skála, Niklas, Lindahl, Iva, Matolínová, Henrik, Grönbeck, Konstantin M, Neyman, Vladimír, Matolín, and Björn, Wickman
- Abstract
Platinum is the most widely used and best performing sole element for catalyzing the oxygen reduction reaction (ORR) in low-temperature fuel cells. Although recyclable, there is a need to reduce the amount used in current fuel cells for their extensive uptake in society. Alloying platinum with rare-earth elements such as yttrium can provide an increase in activity of more than seven times, reducing the amount of platinum and the total amount of catalyst material required for the ORR. As yttrium is easily oxidized, exposure of the Pt-Y catalyst layer to air causes the formation of an oxide layer that can be removed during acid treatment, leaving behind a highly active pure platinum overlayer. This paper presents an investigation of the overlayer composition and quality of Pt
- Published
- 2019
30. Nanoscale Morphological and Structural Transformations of PtCu Alloy Electrocatalysts during Potentiodynamic Cycling
- Author
-
Ivan Khalakhan, Milan Dopita, Mykhailo Vorokhta, Olaf Brummel, Manon Bertram, Iva Matolínová, Vladimír Matolín, Peter Kúš, Yurii Yakovlev, Jörg Libuda, and Fabian Waidhas
- Subjects
Materials science ,Absorption spectroscopy ,Alloy ,Proton exchange membrane fuel cell ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,General Energy ,Chemical engineering ,chemistry ,engineering ,Physical and Theoretical Chemistry ,Thin film ,0210 nano-technology ,Platinum ,Bimetallic strip - Abstract
PtCu bimetallic alloys are known to provide better activity than pure platinum in proton exchange membrane fuel cells. However, such catalysts undergo complex degradation processes during fuel cell operation, resulting in deterioration of their activity. By using in situ electrochemical (EC) atomic force microscopy combined with in situ EC infrared reflection absorption spectroscopy, we provide a comprehensive investigation of morphological and structural transformations of PtCu model thin film catalysts during accelerated degradation tests (ADTs). The ADTs consist of potentiodynamic cycling to three different upper potentials relevant for different modes of fuel cell operation. The results show that, depending on the upper potential limit, PtCu alloy electrocatalysts are subject to drastic changes in the surface composition, morphology, and structure.
- Published
- 2018
31. Origin of negative resistivity slope in U-based ferromagnets
- Author
-
Ladislav Havela, Silvie Mašková, Milan Dopita, I. Tkach, V. Buturlim, and M. Paukov
- Subjects
Materials science ,Magnetoresistance ,Condensed matter physics ,Scattering ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Atomic units ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Weak localization ,Condensed Matter::Materials Science ,Paramagnetism ,Ferromagnetism ,Electrical resistivity and conductivity ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Electrical and Electronic Engineering ,010306 general physics ,0210 nano-technology - Abstract
Ultra-nanocrystalline UH3-based ferromagnets with TC ≈ 200 K exhibit a flat temperature dependence of electrical resistivity with a negative slope both in the ferromagnetic and paramagnetic range. The ordered state with randomness on atomic scale, equivalent to a non-collinear ferromagnetism, can be affected by magnetic field, supressing the static magnetic disorder, which reduces the resistivity and removes the negative slope. It is deduced that the dynamic magnetic disorder in the paramagnetic state can be conceived as continuation of the static disorder in the ordered state. The experiments, performed for (UH3)0.78Mo0.12Ti0.10, demonstrate that the negative resistivity slope, observed for numerous U-based intermetallics in the paramagnetic state, can be due to the strong disorder effect on resistivity. The resulting weak localization, as a quantum interference effect which increases resistivity, is gradually suppressed by enhanced temperature, contributing by electron-phonon scattering, inelastic in nature and removing the quantum coherence.
- Published
- 2018
32. Laves phase UTi2 stabilized by hydrogen and its magnetic properties
- Author
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Milan Dopita, Ladislav Havela, Peter Minárik, M. Paukov, S. Sowa, V. Buturlim, Daria Drozdenko, N.-T.H. Kim-Ngan, and Silvie Mašková
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Hydride ,Intermetallic ,02 engineering and technology ,Laves phase ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Paramagnetism ,Lattice constant ,Ferromagnetism ,Phase (matter) ,0103 physical sciences ,Electrical and Electronic Engineering ,0210 nano-technology ,Ground state - Abstract
We describe basic magnetic properties of uranium-based hydrides UTi2Hx, reported in literature as a cubic Laves phase, although the UTi2 binary phase does not exist. Using a high-temperature hydrogenation, we successfully synthesized two types of such hydrides, presumably with different H concentrations, one with a smaller lattice parameter a = 850.3 pm, which is a paramagnet close to the verge of magnetic ordering, the other with a = 858.8 pm, with a ferromagnetic ground state and ordering temperature TC = 54 K.
- Published
- 2018
33. A Janovec‐Kay‐Dunn‐Like Behavior at Thickness Scaling in Ultra‐Thin Antiferroelectric ZrO 2 Films (Adv. Electron. Mater. 11/2021)
- Author
-
Milan Dopita, Sebastian E. Reyes-Lillo, Yasmin Mohamed Yousry, Nujhat Tasneem, Josh Kacher, Asif Islam Khan, Nazanin Bassiri-Gharb, and Mengkun Tian
- Subjects
Materials science ,Condensed matter physics ,Antiferroelectricity ,Electron ,Scaling ,Electronic, Optical and Magnetic Materials - Published
- 2021
34. A Janovec‐Kay‐Dunn‐Like Behavior at Thickness Scaling in Ultra‐Thin Antiferroelectric ZrO 2 Films
- Author
-
Mengkun Tian, Yasmin Mohamed Yousry, Josh Kacher, Milan Dopita, Sebastian E. Reyes-Lillo, Asif Islam Khan, Nazanin Bassiri-Gharb, and Nujhat Tasneem
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,0103 physical sciences ,Antiferroelectricity ,Cubic zirconia ,02 engineering and technology ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,Scaling ,Electronic, Optical and Magnetic Materials - Published
- 2021
35. Structure identification of Fe–Fe x O y core–shell nanoparticles and their time stability
- Author
-
Tereza Vaclavu, Jan Filip, Daniel Niznansky, Michal Vaclavu, Jan Endres, Milan Dopita, and Stanislav Danis
- Subjects
Inorganic Chemistry ,Structural Biology ,General Materials Science ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Biochemistry - Published
- 2021
36. Fast Debye equation calculation on graphics processing units – GPU used for calculation and fitting of nanoparticle real structure
- Author
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Milan Dopita, Lukáš Horák, Václav Holý, and Martin Rudolph
- Subjects
Inorganic Chemistry ,Structural Biology ,General Materials Science ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Biochemistry - Published
- 2021
37. MGML – Materials Growth and Measurement Laboratory
- Author
-
Pavel Javorský, Jan Prokleška, Klára Uhlířová, Petr Čermák, Milan Dopita, and Martin Žáček
- Subjects
Inorganic Chemistry ,Structural Biology ,General Materials Science ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Biochemistry - Published
- 2021
38. Phase transformations in Ti–Nb–Zr–Ta–O beta titanium alloys with high oxygen and reduced Nb and Ta content
- Author
-
Dalibor Preisler, Josef Stráský, Petr Harcuba, Tereza Košutová, Milan Dopita, Michaela Janovská, Michal Hájek, and Miloš Janeček
- Subjects
Inorganic Chemistry ,Structural Biology ,General Materials Science ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Biochemistry - Published
- 2021
39. Time evolution of Au and Ag nanofluids prepared by direct deposition of gas aggregated nanoparticles into the liquid polymer
- Author
-
Tereza Košutová, Daniil Nikitin, Pavel Pleskunov, Renata Tafiichuk, Andrei Choukourov, and Milan Dopita
- Subjects
Inorganic Chemistry ,Structural Biology ,General Materials Science ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Biochemistry - Published
- 2021
40. Residual- and linker-free metal/polymer nanofluids prepared by direct deposition of magnetron-sputtered Cu nanoparticles into liquid PEG
- Author
-
Pavel Pleskunov, Miroslav Cieslar, Marian Varga, Jan Hanuš, Andrei Choukourov, Daniil Nikitin, Mariia Protsak, Lukáš Ondič, Kateryna Biliak, Milan Dopita, Ksenia Kishenina, Tomáš Popelář, and Renata Tafiichuk
- Subjects
chemistry.chemical_classification ,Materials science ,technology, industry, and agriculture ,Polymer ,Polyethylene glycol ,Sputter deposition ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Metal ,Colloid ,chemistry.chemical_compound ,Nanofluid ,Chemical engineering ,chemistry ,visual_art ,Cavity magnetron ,PEG ratio ,Materials Chemistry ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry ,Spectroscopy - Abstract
Colloidal solutions of metal nanoparticles (NPs) are typically produced by multi-step methods using a variety of chemicals. Resultant nanofluids require extra purification steps to remove the reactions by-products and modification steps to introduce anticoagulants for the solution stabilization. Here, we suggest a single-step method to produce nanofluid in which only two components are present: 22 nm-sized Cu NPs as a filler and polyethylene glycol (PEG, 400 g/mol) as a liquid base. The method employs magnetron sputtering to synthesize Cu NPs in a gas aggregation cluster source and their subsequent loading into vacuum-compatible PEG. The resultant nanofluid demonstrates strong plasmonic and photoluminescent activity, and shows enhanced stability over time, in contrast to conventional colloidal solutions. The approach offers an alternative for the production of nanofluids in which the processes of the NP formation are decoupled from the processes of their mixing with the liquid base.
- Published
- 2021
41. A Facile Way for Acquisition of a Nanoporous Pt–C Catalyst for Oxygen Reduction Reaction
- Author
-
Iva Matolínová, Peter Kúš, Ivan Khalakhan, Mykhailo Vorokhta, Xianxian Xie, Jaroslava Nováková, Kateřina Veltruská, Yurii Yakovlev, Milan Dopita, and Thu Ngan Dinhová
- Subjects
Materials science ,Chemical engineering ,Mechanics of Materials ,Nanoporous ,Mechanical Engineering ,Oxygen reduction reaction ,Fuel cells ,Sputter deposition ,Porous catalyst ,Pt c catalyst - Published
- 2021
42. Microstructure development of ultra fine grained Mg-22 wt%Gd alloy prepared by high pressure torsion
- Author
-
H.S. Kim, Miloš Janeček, Milan Dopita, Jung Gi Kim, T. Vlasák, Radomír Kužel, Tomáš Krajňák, Tomáš Kmječ, Peter Minárik, Jakub Čížek, Petr Hruška, M. Vlček, and Michaela Šlapáková
- Subjects
010302 applied physics ,Materials science ,Mechanical Engineering ,Alloy ,Metallurgy ,Torsion (mechanics) ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Critical value ,Microstructure ,01 natural sciences ,Grain size ,Positron annihilation spectroscopy ,Mechanics of Materials ,0103 physical sciences ,engineering ,General Materials Science ,Crystallite ,Dislocation ,0210 nano-technology - Abstract
A hardenable lightweight Mg-22 wt%Gd alloy with ultra fine grained (UFG) structure was prepared by high pressure torsion (HPT) at ambient temperature. The development of microstructure during HPT processing was investigated. A homogeneous UFG structure with grain size of 300 nm was achieved after 15 HPT revolutions. The UFG alloy exhibits enhanced strength due to work strengthening by tangled dislocations forming a dense forest throughout grains. Dislocation density in the sample was determined by positron annihilation spectroscopy (PAS) and X-ray line profile analysis (XLPA). It was found that there is an additional source of X-ray profile broadening in addition to small crystallites and micro-strains caused by dislocations. The additional micro-strain component was attributed to lattice modulation by Gd-rich nano-wires formed by agglomeration of Gd solutes and to strains arising from boundaries of crystallite domains and inter-domain interactions. Analysis of the influence of the crystallite size on the strength of UFG Mg-22 wt%Gd alloy revealed a breakdown in the Hall-Petch relationship when the crystallite size decreased below a critical value of ≈30 nm.
- Published
- 2017
43. In situ probing of magnetron sputtered Pt-Ni alloy fuel cell catalysts during accelerated durability test using EC-AFM
- Author
-
Roman Fiala, Milan Dopita, Vladimír Matolín, Ivan Khalakhan, Peter Kúš, Nataliya Tsud, Mykhailo Vorokhta, Tomáš Skála, and Michal Václavů
- Subjects
Materials science ,Annealing (metallurgy) ,General Chemical Engineering ,Alloy ,Analytical chemistry ,02 engineering and technology ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Durability ,0104 chemical sciences ,X-ray photoelectron spectroscopy ,Chemical engineering ,Cavity magnetron ,Electrochemistry ,engineering ,Chemical stability ,Thin film ,0210 nano-technology ,Spectroscopy - Abstract
As-deposited Pt-Ni and annealed Pt-Ni alloy catalyst films prepared by magnetron co-sputtering were investigated in order to quantify their ageing during accelerated durability test. The parameters of the durability test were chosen to simulate severe potential conditions that may occur at start-up/shut-down cycles of a fuel cell. Using in situ electrochemical atomic force microscopy complemented with ex situ energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, synchrotron radiation photoelectron spectroscopy and X-ray diffraction provided step-by-step correlation of chemical and morphology changes induced by catalyst’s aging processes. We show that the as-deposited Pt-Ni films face severe chemical stability problem which leads to almost complete destruction of the alloy during the durability test. On the other hand Pt-Ni films annealed in vacuum are more resistive to morphological and chemical changes. It was confirmed that upon annealing due to redistribution of Pt and Ni atoms Pt-skin is formed on catalyst surface, which is responsible for a better stability during the aging test.
- Published
- 2017
44. Formation of different alumina phases and magnesium aluminate spinel during contact of molten AlSi7Mg0.6 alloy with mullite and amorphous silica
- Author
-
Claudia Voigt, Milan Dopita, Christos G. Aneziris, Anton Salomon, Tilo Zienert, Olga Fabrichnaya, and David Rafaja
- Subjects
010302 applied physics ,Materials science ,General Chemical Engineering ,Alloy ,Spinel ,Metallurgy ,Spark plasma sintering ,Mullite ,02 engineering and technology ,General Chemistry ,engineering.material ,021001 nanoscience & nanotechnology ,01 natural sciences ,Aluminium alloy inclusions ,visual_art ,0103 physical sciences ,5052 aluminium alloy ,engineering ,Aluminium alloy ,visual_art.visual_art_medium ,6063 aluminium alloy ,General Materials Science ,0210 nano-technology - Abstract
Corrosion of alumina-based metal melt filters functionalized by 3Al2O3·2SiO2 or fused SiO2 was investigated using local chemical and microstructure analyses and thermodynamic calculations. Molten aluminium alloy AlSi7Mg0.6 was employed as corrosion medium. The aluminium alloy was melted in a Spark Plasma Sintering apparatus in order to avoid the melt flow. During the reaction with the AlSi7Mg0.6 melt, 3Al2O3·2SiO2 partly decomposed, and Al2O3 reacted with magnesium from the melt and with oxygen from SiO2 to MgAl2O4. Silicon precipitated in the aluminium alloy. For corundum functionalized by fused SiO2, metastable γ-Al2O3 was detected additionally to the above phases for short reaction times.
- Published
- 2017
45. Mössbauer Spectroscopy of Triphylite (LiFePO4) at Low Temperatures
- Author
-
Jan Kuriplach, Milan Dopita, Tomáš Kmječ, Jaroslav Kohout, and M. Veverka
- Subjects
Materials science ,Condensed matter physics ,Magnetic moment ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,lcsh:QC1-999 ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Ion ,Magnetization ,Magnetic anisotropy ,antiferromagnetic order ,0103 physical sciences ,Mössbauer spectroscopy ,Antiferromagnetism ,lifepo4 ,010306 general physics ,0210 nano-technology ,Hyperfine structure ,mössbauer spectroscopy ,density functional theory ,lcsh:Physics - Abstract
Low temperature magnetic ordering in the LiFePO 4 compound is investigated experimentally using Mö, ssbauer spectroscopy and theoretically via first principles calculations. The evaluation of experiment carried out on a powder sample is compatible with an antiferromagnetic order of Fe ion magnetic moments. When an external magnetic field is applied, Fe magnetic moments start to deviate slightly from the [010] easy magnetization direction. These findings are confirmed by means of first principles calculations, which also suggest the magnitude of single ion magnetic anisotropy and orbital and spin-dipolar contributions to the magnetic hyperfine field, which is eventually in a good agreement with the experiment. Diffraction and magnetic measurements complement the study.
- Published
- 2019
46. Crystal Structure and Magnetic Properties of Uranium Hydride UH
- Author
-
Ladislav, Havela, Mykhaylo, Paukov, Milan, Dopita, Lukáš, Horák, Daria, Drozdenko, Martin, Diviš, Ilja, Turek, Dominik, Legut, Lukáš, Kývala, Thomas, Gouder, Alice, Seibert, and Frank, Huber
- Abstract
A new type of uranium binary hydride, UH
- Published
- 2018
47. Crystal structures and magnetism of the hydrides of Tb2T2Ga and Tb3Co3Ga (T = Co, Ni)
- Author
-
Milan Dopita, Yaroslav Tokaychuk, Roman Gladyshevskii, Nazar Saidov, Khrystyna Miliyanchuk, Silvie Maskova-Cerna, and Ladislav Havela
- Subjects
Materials science ,Hydrogen ,Magnetism ,Hydride ,Intermetallic ,chemistry.chemical_element ,02 engineering and technology ,Crystal structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,Crystallography ,Ferromagnetism ,chemistry ,Materials Chemistry ,Ceramics and Composites ,Antiferromagnetism ,Curie temperature ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
Hydrogenation effects on the crystal structures and magnetic properties of Tb2Co2Ga, Tb2Ni2Ga, and Tb3Co3Ga were studied. Tb2Co2Ga, Tb2Ni2Ga (both structure type W2CoB2), and Tb3Co3Ga (structure type W3CoB3) are structurally related belonging to inhomogeneous linear structure series based on the TlI- (also referred to as CrB type) and YAlGe- (ordered derivative of the binary type UPt2) type structure motives. The hydrides Tb2Co2GaH6.2, Tb3Co3GaH9.7, and Tb2Ni2GaH5.1 were synthesized at room temperature with hydrogen pressures of 52–53 kPa. Hydrogenation results in strongly anisotropic lattice volume expansion ΔV/V = 19.2–20.0%. It also leads to a decrease of the Curie temperature in ferromagnetic Tb2Co2Ga and Tb3Co3Ga and practically suppresses the antiferromagnetic ordering in Tb2Ni2Ga. A model of the crystal structure of the hydride Tb3Co3GaH10 with four hydrogen positions was suggested based on stronger effect of hydrogenation on the TlI-type slabs. The more complex character of the magnetic phase transitions for Tb2Co2Ga and Tb3Co3Ga presumes involvement of Co in the magnetism of these compounds, while Tb2Ni2Ga acts as a typical 4f-electron system with dominating RKKY exchange interactions.
- Published
- 2021
48. Hydrogen in U-T alloys: Crystal structure and magnetism of UH3-V
- Author
-
M. Paukov, Ladislav Havela, V. Buturlim, Milan Dopita, Khrystyna Miliyanchuk, Oleksandra Koloskova, and Peter Minárik
- Subjects
Materials science ,Magnetic moment ,Magnetism ,Mechanical Engineering ,Metals and Alloys ,Vanadium ,chemistry.chemical_element ,Thermodynamics ,02 engineering and technology ,Crystal structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Nanocrystalline material ,0104 chemical sciences ,Ferromagnetism ,chemistry ,Mechanics of Materials ,Phase (matter) ,Materials Chemistry ,Orthorhombic crystal system ,0210 nano-technology - Abstract
U-V alloys with variable phase composition were prepared using ultrafast cooling. 15 at.% V is not sufficient to suppress entirely the orthorhombic α-U type of phase and higher alloying concentrations lead to a segregation of pure vanadium. The alloys are stable with respect to H2 exposure at pressures of 105 Pa. Nevertheless hydrogenation proceeds slowly at high H2 pressures. Resulting hydrides exhibit a common β-UH3 structure. This is unusual among the U-T systems, which yield either α-UH3 or nanocrystalline β-UH3 structures. The UH3-V system is ferromagnetic with the Curie temperatures monotonously increasing with the V concentration to TC = 190 K for 15 at.% V. Magnetic moments remain on the level of 1.0 μB/U. The results prove that the increase of TC in alloyed U hydrides of the UH3-T type does not depend on particular structure details or type of the T element, although the latter modifies somewhat the maximum TC values achieved. The situation can be understood assuming that the substitution of U by T provides an enhanced H/U ratio, while the U-H interaction is a prominent element of the 5f moments formation and ordering.
- Published
- 2021
49. Temperature versus composition phase diagram and temperature evolution of structure and modulation of Ni2MnGa1-xInx single crystals
- Author
-
J. Valenta, Petr Doležal, K. Vlášková, Milan Dopita, Petr Opletal, and Petr Cejpek
- Subjects
Materials science ,Mechanical Engineering ,Metals and Alloys ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Lattice constant ,chemistry ,Mechanics of Materials ,Diffusionless transformation ,Phase (matter) ,Materials Chemistry ,Curie temperature ,0210 nano-technology ,Single crystal ,Indium ,Monoclinic crystal system ,Phase diagram - Abstract
A series of single crystal Ni2MnGa1-xInx samples, varying in compositions between x = 0 to 0.15, were grown by Bridgman method. Critical temperatures were obtained from the magnetisation and electrical resistivity measurements. A Curie temperature and the temperatures of pre-martensitic and martensitic transformation decrease with increasing indium content. The decrease rate is faster than the rate published previously on polycrystalline samples, since no martensitic transformation was observed in our samples with the indium content x > 0.05. The results of X-ray diffraction measurements of low temperature martensitic phase show significant decrease of monoclinic lattice parameter a and increase of monoclinic lattice parameter c and γ angle with respect to increasing indium content. Composition dependence was observed also for the modulation vector in martensitic and pre-martensitic phase, where its x and y coordinates gain values around 3/7 and 1/3 respectively.
- Published
- 2021
50. Role of disorder in magnetic and conducting properties of U–Mo and U–Mo–H thin films
- Author
-
Ladislav Havela, F. Huber, Lukáš Horák, Oleksandra Koloskova, Milan Dopita, Zbyněk Šobáň, M. Paukov, A. Seibert, Thomas Gouder, and E.A. Tereshina-Chitrova
- Subjects
Materials science ,Condensed matter physics ,Hydride ,02 engineering and technology ,Sputter deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Amorphous solid ,Weak localization ,Curie temperature ,General Materials Science ,Texture (crystalline) ,Thin film ,0210 nano-technology ,Critical field - Abstract
Crystal structure, magnetic and electrical properties of thin U–Mo films and their hydrides prepared by reactive sputter deposition from metallic targets were studied. The films are metallic but with high values of electrical resistivity. Both bcc U0.79Mo0.21 thin film and the hydride (UH3)0.74Mo0.26 (β-UH3 structure type) have a very strong texture. Superconductivity is identified below Tc = 0.55 K for U0.79Mo0.21. The critical field of 1.0 T is exceeding that of α-U (0.3 T). The hydride film (UH3)0.74Mo0.26 is a ferromagnet with the Curie temperature TC = 165 K, higher concentration of Mo somewhat reduces the TC value. Deposition on a cooled substrate reduces the grain size of the hydride, approaching the limit of amorphous state. The U–Mo films and hydrides exhibit the net negative temperature coefficient of resistivity, TCR = dρ/dT, attributed to the randomness on atomic scale, yielding very strong scattering of electrons and weak localization.
- Published
- 2021
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