Finished projects

Impact of radiation on distinctive physical properties of advanced materials for nuclear facilities
GAČR 14-12449S (2014-2016)

Guarantees:
prof. Ing. Marcel Miglierini, DrSc. (FJFI ČVUT)
Ing. Adriana Lančok, Ph.D. (UACH AV ČR)
doc. Mgr. Jaroslav Kohout, Dr. (MFF UK)


The long-term reliability of construction materials operating in nuclear facilities under harsh conditions: intense radiation, high temperature, and in the presence of corrosion agents is a serious technologic, economic, and environmental demand. In this project, we shall elucidate the impact of irradiation upon surface and bulk physical properties including structural arrangements and magnetic ordering in advanced alloys. They comprise metallic glasses and nanocrystalline alloys for particle accelerators and construction steels for nuclear reactors. Structural transformations (amorphous to nanocrystalline) and modifications imposed by thermal treatment and irradiation by ions and/or neutrons will be studied by Mössbauer and NMR spectroscopy and by nuclear forward scattering of synchrotron radiation employing 57Fe nuclei as local probes of hyperfine interactions in the studied materials. Originality of the expected results rests with our effort to determine the relationship between structural arrangement and magnetic state as depending on different types of structural modifications.

Magnetic, ferroelectric and relaxor properties and their cross coupling in relaxor perovskite multiferroics
GAČR P204/13/11473S (2013-2016)

Guarantees:
Valentyn Laguta, DrSc. (FZU AV ČR)
prof. RNDr. Helena Štěpánková, CSc. (MFF UK)


Magnetoelektrická relaxorová multiferoika vykazují kromě současné přítomnosti feroelektrického a magnetického uspořádání také vlastnosti spinových a dipólových skel nebo relaxorových neergodických fází. Tyto vlastnosti souvisejí s nehomogenitami v nanometrické škále indukovanými neuspořádaností poloh iontů a nábojových stavů. Kombinace a řízení různých stupňů uspořádanosti nabízí nové možnosti, jak získat materiály s novými funkčními vlastnostmi směřujícími k technickým aplikacím. V projektu objasníme podstatu termodynamických fází s různými typy spinového a dipólového uspořádání a s různou magnetoelektrickou (ME) vazbou pro skupinu relaxačních multiferoik založených na perovskitech Pb(Fe2/3W1/3)O3 a Pb(Fe1/2Nb1/2)O3. K řešení budou využity různé jak lokální, tak makroskopické charakterizační techniky (NMR, EPR, Mössbauerova, magnetická a dielektrická spektroskopie), a to ve vzájemné součinnosti s teoretickým modelováním. Budou objasněny mechanismy formování multiferoických fází a ME cross-coupling efektů na atomární úrovni a specifikovány cesty ke zlepšení ME charakteristik.

Hyperfine interactions in multiferroics
GAUK 107-10/253354 (2012-2015)

Guarantees:
Mgr. Tomáš Kmječ (MFF UK)
doc. Mgr. Jaroslav Kohout, Dr. (MFF UK)
Mgr. Denisa Kubániová (MFF UK)
RNDr. Karel Závěta, CSc. (FZU AV ČR)

Multiferroics combining magnetic and ferroelectric ordering are at the forefront of basic research for their high application potential. They are used in spintronics, memory elements, as sensors or detectors. Hyperfine interactions yield information about ordering in multiferroics and contribute to the understanding of microscopical mechanism of magnetoelectric effect – coupling of magnetic and electric moments. Mössbauer spectroscopy, using 57Fe nucleus as local probe, is the basic method to study hyperfine interactions. It provides information on valences of iron atoms and their magnetic moments in different crystallographic sites, local crystal symmetry and the effect of cation surrounding. In the first year of the project we shall prepare and characterize ε-Fe2O3 nanoparticles showing promising magnetic and multiferroic properties for data storage. With selected samples dependences of hyperfine parameters on temperature and magnetic field up to 6T will be measured. In the next years we suppose investigations of magnetite (Fe3O4), which displays multiferroic properties under the temperature of Verwey transition (TV~125K) and perovskite samples with chemical composition Pb(Fe1/2Nb1/2)O3, Pb(Fe2/3W1/3)O3 where the ferroelectric transition occurs under ~380 K, but the temperatures of magnetic transitions are not yet well determined. DC magnetic measurements, XRD, SEM, TEM and EDXRF will be used for sample characterization.

Program rozvoje vědních oblastí na Univerzitě Karlově
PRVOUK 107-04/1107 (2011-2015)

Program navazuje na čtyři výzkumné záměry úspěšně řešené fyzikální sekcí MFF UK v posledních letech a zahrnuje tak rozvoj veškerého fyzikálního výzkumu na fakultě. Program odpovídá dlouhodobému záměru rozvoje výzkumu na MFF UK a zaměřuje na čtyři stěžejní oblasti. Oblast Fyzika kondenzované fáze – nové materiály a technologie se zaměřuje na komplexní studium souvislostí reálné elektronové, atomové a magnetické struktury s objemovými a povrchovými fyzikálními vlastnostmi makroskopických, mezoskopických i nanostrukturních systémů. Organickou součástí je vývoj a využití nejnovějších technologií přípravy a charakterizace vysoce kvalitních materiálů s definovanými fyzikálními vlastnostmi.

Hyperfine interactions in nanosized and low-dimensional iron oxides
GAČR P204/10/0035 (2010-2014)

Guarantees:
doc. Mgr. Jaroslav Kohout, Dr. (MFF UK)
Ing. Adriana Lančok, Ph.D. (UACH AV ČR)
Ing. Miroslav Veverka, Ph.D. (FZU AV ČR)


Miniaturization of electronic elements including magnetic ones concentrates interest on systems of magnetic nanoparticles motivated by their broad application potential especially in medicine (increase of MRI contrast, magnetic hyperthermia, targeted transport). The aim of the project is to use the study of hyperfine interactions for elucidation of new specific properties of magnetic nanosystems connected to the growing influence of the surface effects with the decrease of the particle sizes. For this purpose we shall use the combination of Mössbauer Spectroscopy and NMR with high resolution yielding a slightly different and complementary spectrum of information. With respect to the isotope specificity of both methods we shall deal with the iron compounds where in particular the nuclei of the stable isotope 57Fe will be the local probe. The decisive role for the successful handling of the project will be played by the production of required materials – nanoparticles of Fe oxides with the spinel and hexagonal structures including their nanocomposites in various matrices.

Study of xerogels by means of Mössbauer spectroscopy
GAČR 203/07/P011 (2007-2009)

Guarantees:
Ing. Adriana Lančok, Ph.D. (UACH AV ČR)


A large variety of glasses and glass ceramics may be obtained by sol-gel process from hydrolysis of tetraethoxysilane. The overall transformation evolves by hydrolysis and polycondensation reactions leading to the growth of clusters that eventually collide together to form a gel. The structure and properties of the final product have been found to be strongly dependent on the initial conditions of preparation.The project will deal with silica xerogels based on Fe2O3/SiO2 prepared by help of ultrasonic activation and subsequent annealing in nitrogen atmosphere or air with the concentration of iron oxide about 20 to 30 wt.%. The goal of this project is the study of xerogel materials particularly by means of Mössbauer spectroscopy and aims at detailed characterisation of systems and effects of condition of preparation on their structuralisation. The search of optimum conditions for design and synthesis of hybrid materials and nanocomposites possessing targeted properties, and the ...