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Nanostructured materials based on metal oxides - structure and thermal stability
Václavů, Tereza ; Kužel, Radomír (advisor) ; Čapková, Pavla (referee) ; Klementová, Mariana (referee)
Title: Nanostructured materials based on metal oxides - structure and thermal stability Author: Tereza Václavů Department: Department of Condensed Matter Physics Supervisor: prof. RNDr. Radomír Kužel, CSc. Abstract: The structure and temperature stability of two nanocrystalline ma- terials were studied. First, titanate nanotubes prepared by hydrothermal synthesis were studied from room temperature up to 1000 ◦ C in air and helium atmospheres and in vacuum with the aid of in situ X-ray diffraction (XRD) and calorimetry combined with electron microscopy. The nanotubes exhibit different behavior and structure transformations during heating in different atmospheres. A difference between vacuum and He atmosphere was observed; also a different final product was observed after annealing: In air, the nanorods disintegrated to nanoparticles, whereas in vacuum nanowires formed. The second material studied was a nanocrystalline particle system with an iron core protected against oxidation by an oxide layer. The structure of these nanoparticles was determined by XRD and Mossbauer spectroscopy. The tem- perature stability and induced transformations of these samples were studied by in situ XRD and X-ray small-angle scattering (SAXS). The long-time stability of the structure of these nanoparticles was studied as well;...
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Structure analysis of some transition metal silicides using X-ray diffraction and dynamical refinement against electron diffraction data
Antunes Corrêa, Cinthia ; Janeček, Miloš (advisor) ; Kalvoda, Ladislav (referee) ; Kužel, Radomír (referee)
Title: Structure analysis of some transition metal silicides using X-ray diffraction and dynamical refinement against electron diffraction data Author: Cinthia Antunes Corrˆea Department: Physics of Materials Supervisor: prof. RNDr. Miloš Janeček, CSc., Department of Physics of Materials Abstract: This thesis presents the crystal structure analysis of several transition metal silicides. The crystal structures were studied primarily by precession electron diffraction tomography (PEDT) employing the dynamical refinement, a method recently developed for accurate crystal structure refinement of electron diffraction data. The optimal values of the parameters of the method were proposed based on the comparison between the dynamical refinement of PEDT data and a high- quality reference structure. We present the results of the comparison using a Ni2Si nanowire with the diameter of 15 nm. The average atomic distance between the model obtained by the dynamical refinement on PEDT data and the one by single crystal X-ray diffraction was 0.006 ˚A. Knowing the accuracy and limitations of the method, the crystal structure of Ni3Si2 was redetermined on a nanowire with 35 nm of diameter. The model obtained had an average error in the atomic posi- tions of 0.006 ˚A. These results show that the accuracy achieved by the dynamical...
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Structure of submicrocrystalline materials studied by X-ray diffraction
Matěj, Zdeněk ; Kužel, Radomír (advisor) ; Lukáš, Petr (referee) ; Čerňanský, Marian (referee)
Structure of submicrocrystalline materials was investigated by X-ray powder diffraction, mainly by modelling of widths and shapes of diffraction profiles. The diffraction method was applied to colloid gold nanoparticles, copper samples deformed by equal channel angular pressing and titanium dioxide nanoparticles prepared by various chemical routes. Dislocations and twin faults were identified in the metallic samples from characteristic broadening of diffraction lines. Densities of lattice defects were estimated from the diffraction data. Possibilities and limits of the diffraction method for characterisation of a crystallite size distribution were tested on the titanium dioxide samples. Crystallites of size in the range 3-25 nm could be well characterised. The problems were encountered only for samples with extremely broad size dispersion. Diffraction methods and a computer program were developed and tested, which can be applied also for the analysis of thin films.
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Determination of the amount of the amorphous phase using x-ray diffraction
Málek, Tomáš ; Daniš, Stanislav (advisor) ; Kužel, Radomír (referee)
Using quantitative analysis based on x-ray diffraction entails complication in the amorphous phase contribution to signal background which may affect results. Often it is impossible to ignore this contribution and thus is appropriately to use some method for separation of the amorphous phase contribution from signal eventually also determine amount of amorphous phase in the sample. Although x-ray diffraction is used for crystalline samples is almost inevitable keep sample clear from amorphous phase which is in all polycrystalline sample in some amount. In this thesis we will effort to determine method or combination of methods which is possible to use for determination of the amount of the amorphous phase that we can use for cleaning results of quantitative analysis from the amorphous phase contribution.
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Microstructure and properties of multiferroic complex oxide thin films prepared by pulsed laser deposition method
Machovec, Petr ; Dopita, Milan (advisor) ; Kužel, Radomír (referee)
Title: Microstructure and properties of multiferroic complex oxide thin films prepared by pulsed laser deposition method Author: Petr Machovec Department: Department of Condensed Matter Physics Supervisor: RNDr. Milan Dopita, Ph.D., Department of Condensed Matter Physics Abstract: In the frame of this thesis, structure, microstructure, and real structure of multiferroic epitaxial layers of LuFeO3 were studied by means of X-ray reflectivity and X-ray diffraction. In theoretical part the theory of X-ray scattering on crystalline layers is described. Standard description of X-ray reflectivity on series of rough layers is presented. Moreover, a model of X-ray scattering on mosaic layer is described. For experimental part of the work three samples were prepared by pulsed laser deposition method. First sample on sapphire substrate (Al2O3), second on platinum layer deposited on sapphire substrate and third on yttrium stabilized zirconia substrate. From the X-ray reflectivity curves the parameters such as layer thickness, interface roughness, surface roughness and material density, were determined. By analysing measured reciprocal space maps, lattice parameters and mosaic model parameters, such as mean mosaic block size, mosaic block size distribution, mosaic block misorientation and residual microstrain, were...
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Oxygen-strengthened biomedical beta titanium alloys
Preisler, Dalibor ; Stráský, Josef (advisor) ; Kužel, Radomír (referee)
Oxygen strengthened biomedical beta titanium alloys Beta titanium alloy Ti-35Nb-6Ta-7Zr-0.7O (wt. %) exhibits a low Young's modulus and high strength thanks to interstitial strengthening effect of oxygen. These mechanical properties are promising for implant production. In this thesis, the aforementioned alloy is thoroughly studied in conditions prepared by various thermomechanical treatments, namely: material after casting, hot compression testing, die-forging, hot rolling and finally, cold-swaged and annealed condition. Mechanical properties and microstructure of prepared conditions are studied with special interest of enhancing the fatigue performance that is poor after casting due to porosity and large grains. The hot rolling was shown to improve the fatigue performance significantly, mainly through grain refinement. It is shown that by combining the effects of cold-swaging and recrystallization annealing, extensive refinement of grain structure can be achieved. Industrial aspects of implant production by the studied methods were discussed. In the second part of the thesis, the possibility of lowering the Young's modulus by reducing the beta phase stability (by reducing of Nb and Ta content), while retaining high strength caused by high interstitial oxyen content is explored. Several alloys were...
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Structural study of nanocrystalline titanium oxide films and their temperature stability
Chlanová, Lea ; Kužel, Radomír (advisor) ; Čapková, Pavla (referee) ; Ganev, Nikolaj (referee)
Title: Structural study of nanocrystalline titanium oxide films and their temperature stability Author: Lea Chlanová Department: Department of Condensed Matter Physics Supervisor: Prof. RNDr. Radomír Kužel, CSc., Department of Condensed Matter Physics Abstract: TiO2 thin films can exhibit photocatalytic activity and photoinduced su- perhydrophilicity depending on crystallinity, phase composition and mi- crostructure. These parameters were studied by X-ray diffraction (XRD) and reflectivity (XRR) for magnetron deposited films - nanocrystalline and amorphous, namely their temperature and time evolution. For nanocrystalline films, it was found that higher partial oxygen pressure during the deposition is beneficial. Small anatase crystallites were stable up to about 450 ◦ C. Depth-profiling XRD of some samples revealed that rutile phase was only present close to the substrate. For amorphous films it was found that the crystallization depends strongly on the film thickness and it is slower for very thin films. Evolution of the intensities of anatase diffraction peaks with annealing time could be described by a modified Avrami equation. XRD profile was relatively narrow from the very be- ginning of crystallization (at about 220 ◦ C), which indicated relatively larger crystallites (> 100 nm), and hence, nanocrystalline films...
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Structure analysis of some transition metal silicides using X-ray diffraction and dynamical refinement against electron diffraction data
Antunes Corrêa, Cinthia ; Janeček, Miloš (advisor) ; Kalvoda, Ladislav (referee) ; Kužel, Radomír (referee)
Title: Structure analysis of some transition metal silicides using X-ray diffraction and dynamical refinement against electron diffraction data Author: Cinthia Antunes Corrˆea Department: Physics of Materials Supervisor: prof. RNDr. Miloš Janeček, CSc., Department of Physics of Materials Abstract: This thesis presents the crystal structure analysis of several transition metal silicides. The crystal structures were studied primarily by precession electron diffraction tomography (PEDT) employing the dynamical refinement, a method recently developed for accurate crystal structure refinement of electron diffraction data. The optimal values of the parameters of the method were proposed based on the comparison between the dynamical refinement of PEDT data and a high- quality reference structure. We present the results of the comparison using a Ni2Si nanowire with the diameter of 15 nm. The average atomic distance between the model obtained by the dynamical refinement on PEDT data and the one by single crystal X-ray diffraction was 0.006 ˚A. Knowing the accuracy and limitations of the method, the crystal structure of Ni3Si2 was redetermined on a nanowire with 35 nm of diameter. The model obtained had an average error in the atomic posi- tions of 0.006 ˚A. These results show that the accuracy achieved by the dynamical...
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