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Complete series of lanthanide oxalates: Structure and properties
Uríková, Daniela Veronika ; Tyrpekl, Václav (advisor) ; Hynek, Jan (referee)
Metal oxalates are salts of very low solubility allowing an easy precipitation of metal ions from the acidic aqueous solutions into crystalline material. Due to this property, oxalates have an important role in the technology of lanthanides and actinides. It is namely the separation of actinides from the spent nuclear fuel that is its industrial application of interest. 4f-lanthanides are often used as 5f-actinides surrogates when optimizing or modelling the precipitation process. A synthetic route for homogeneous precipitation of oxalates based on the thermal decomposition of oxamic acid was developed by our research team. The present work deals with further investigation into the structure and morphology of simple lanthanide oxalates. The synthesis products, developed microcrystals, were studied by means of solid-state analysis (optical microscopy, single crystal X-ray diffraction, X-ray powder diffraction, TGA, SEM, AFM). Among the known, the previously not-specified structures of Er2(C2O4)3∙6H2O and Yb2(C2O4)3∙6H2O were obtained and refined. According to our observations, the synthesized oxalates form two isostructural series: decahydrates and hexahydrates. Structurally, both types of Ln oxalates form 2D frameworks that are stacked together in one direction and connected by hydrogen bonds to...
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Molecular Crystals for Nonlinear Optics - Salts of Nitrogen-containing Bases with Selenious Acid and Hypophosphorous Acid
Němcová, Tereza ; Matulková, Irena (advisor) ; Tyrpekl, Václav (referee)
In this bachelor thesis, systems of selenious acid and hypophosphorous acid with six organic bases (2-aminopyrimidine, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, 3,5-diamino-1,2,4-triazole, 2-aminoguanidine and biguanide) were studied as the source of new materials for nonlinear optics. The six prepared crystalline compounds were identified and characterized by vibrational spectroscopy and X-ray diffraction. Unfortunately, all prepared salts contain a centre of symmetry in their structures, and therefore none of them are suitable for nonlinear optics especially the second harmonic generation.
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Synthesis and properties of transition metal carbides
Nedvědová Šolcová, Pavlína ; Tyrpekl, Václav (advisor) ; Zákutná, Dominika (referee)
This master thesis is a follow-up of my bachelor's project, where the goal was to prepare high entropy carbide (HEC), namely (Ti, Zr, Hf, Nb, Ta)C, by the sol-gel method followed by carbothermal reduction using spark plasma sintering facility (SPS). In this work, the first aim is to substitute SPS with ultra-fast high-temperature sintering (UHS) for the same HEC, (Ti, Zr, Hf, Nb, Ta)C. The advantages of UHS compared to SPS are a thousand times lower consumption of electricity and simpler set-up. The second aim is the adaptation of the synthesis for the preparation of HEC of different compositions, (Cr, Mn, Fe, Co, Ni)C. The third aim is the testing of the presented sol-gel technique on the production of borides, while the initial experiments were focused on boro- carbothermal reduction. Keywords: high entropy carbides, high entropy borides, transition metals, carbothermal reduction, high-temperature ceramics, sol-gel method
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Transition metal oxides for chemical sensors
Volfová, Lenka ; Tyrpekl, Václav (advisor) ; Zelinger, Zdeněk (referee) ; Myslík, Vladimír (referee)
Outdoor air pollution is one of the main environmental problems today. Its monitoring is, among other things, given by the European Union directive (2008/50/EC) on air quality and places high demands on the quantity and reliability of sensors deployed in our immediate surroundings. In order to continuously monitor large number of habitats, it is necessary to develop simple and inexpensive types of sensors. Figure 1 shows an example of such a sensor. The topic of the dissertation is the preparation by physical methods and the study of the surfaces of thin oxide layers as an active medium for the above-mentioned applications. The thesis investigates the possibility of materials preparation by pulsed laser deposition, discharge in a hollow cathode and magnetron sputtering thin film materials for chemiresistor sensors based on copper and tungsten oxides, luminescent Eu doped ZnO layers and resonant so-called QCM, where a quartz resonator was covered with a layer of black aluminium showing a large specific surface in order to increase the sensitivity of these types of sensors. Since the state and properties of the surface are crucial for the function of these types of sensors, an integral and important part of the work is the characterization of the structural properties of the prepared layers,...
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Synthesis of novel porous coordination polymers, their characterization and solvothermal stability
Ondrušová, Soňa ; Lang, Kamil (advisor) ; Tyrpekl, Václav (referee)
This diploma thesis builds on the already published work, in which phosphinate analogs of terephthalic acid were used to prepare new stable metal-organic frameworks (MOFs) Fe-ICR- 2 and Fe-ICR-4. With the use of analogous biphenylene linkers, two new Fe-MOFs were prepared - Fe-ICR-6 and Fe-ICR-7. Isoreticular MOFs were also prepared using Al3+ metal centers. These materials were characterized by X-ray powder diffraction and adsorption isotherm measurements. Their solvothermal stability was measured after shaking and refluxing in water, ethanol, and toluene and activation from water. Furthermore, their thermal stability and the disintegration mechanism in air were determined by thermal analysis. Keywords: coordination polymer, metal-organic framework, stability, phosphinate
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Preparation and Characterization of Iron (III) Oxide Nanocomposites Substituted with Scandium
Kaščáková, Dorota ; Nižňanský, Daniel (advisor) ; Tyrpekl, Václav (referee)
In this work a preparation and characterization of nanoparticles of iron(III) oxide substituted with scandium in SiO2 matrix is described. The nanoparticles were prepared by the sol-gel method yielding mostly β-Fe2O3 substituted with various amount of scandium(III) ions. Mossbauer spectroscopy was carried out to determine purity of the samples and the content of other iron oxides phases. System was characterized by magnetic measurements. Powder X - ray diffraction was used to verify the composition and to determine the lattice parameter and particle size. β-Fe2O3 is formed at the temperatures of 1000 and 1100 ◦ C at composition Fe2−xScxO3 for x ≥ 0.2 and at temperature 1100 ◦ C for x = 0.1. Lattice parameter is linearly dependent on the scandium content and depends also on the annealing temperature. At temperatures higher than 1250 ◦ C, β-Fe2O3 is transformed into hematite. Key words: iron(III) oxide, scandium, sol-gel, Mossbauer spectroscopy, X-ray diffraction, magnetic measurements 1
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Magnetic insulators with hexagonal and cubic structure
Soroka, Miroslav ; Tyrpekl, Václav (advisor) ; Pinkas, Jiří (referee) ; Sedmidubský, David (referee)
Title: Magnetic insulators with hexagonal and cubic structure Author: Mgr. Miroslav Soroka Department: Department of Inorganic Chemistry, Faculty of Science, Charles University of Prague Supervisor: RNDr. Václav Tyrpekl, Ph.D. Consultants: Ing. Josef Buršík, CSc., RNDr. Karel Knížek, Dr. Abstract The presented work deals with the preparation of thin films of transition metal oxides by chemical solution deposition method and the study of their physical properties. Thin films of Z-type (Sr3-xBaxCo2Fe24O41) and W-type (SrCo2-xZnxFe16O27) hexaferrites were prepared with the intention of studying magnetic properties, magneto-electric effect (ME) and spin Seebeck effect (SSE). The study of SSE in hexaferrites as a spin-caloritronic phenomenon was extended by the study of SSE in ε-Fe2-xAlxO3 films and the anomalous Nernst effect (ANE) in La0.7Sr0.3CoO3. Several types of deposition precursors were used for the preparation of thin films: metal alkoxides, 2-ethylhexanoic acid salts and metal citrate complexes. Synthetized materials were structurally characterized by powder X-ray diffraction (pXRD). The texture and orientation relation of the prepared films with substrate were characterized by ω-curves and φ-scan measurements. Scanning transmission electron microscopy (STEM) and atomic force microscopy were used to...
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Physico-chemical properties of oxamic and glyoxylic acids and their affinity to lanthanides
Zakharanka, Anastasiya ; Tyrpekl, Václav (advisor) ; Šubrt, Jan (referee)
This bachelor work focuses on studies of chosen aspects of the basic physicochemical properties of oxamic and glyoxylic acids and their affinity to lanthanides, cerium, and gadolinium taken as the representatives. Room temperature solubilities, pKa values, thermal and photochemical stability of the acids have been evaluated. The acids' affinity to lanthanide (III) ions in an aqueous solution has been studied using various conventional laboratory techniques and instrumental methods. Lanthanide oxalate decahydrates have been synthesized using heterogeneous and homogeneous precipitation routes and characterized using classical solid-state analytical techniques. Keywords: oxalic acid precipitation, oxamic acid, oxamates, oxalates, glyoxylic acid, f-block metals chemistry
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Nonconventional synthesis of high entropy carbides
Šolcová, Pavlína ; Tyrpekl, Václav (advisor) ; Havlíček, David (referee)
This thesis aimed to streamline the method of the preparation of high entropy carbides. The simplification of synthesis and expends reduction were achieved using sol-gel method instead of using commercial starting powders. As precursors of transition metals, the chlorides (TiCl3, TaCl4, HfCl4 a NbCl5) and chlor-oxide (ZrOCl2) were used. The source of carbon was citric acid. All reactants were mixed in solution and dried to gel. The pyrolysis at 800 řC afterwards leads to creation of the amorphous carbon, which embedded the transition metal oxide nanoparticles. The carbothermal synthesis was completed in Spark plasma sintering device at 1400 řC, 1600 řřC and 1900 řC. Formation of high entropy carbide phase was achieved at 1600řC, which is almost 400 řC less than previously reported in literature. Intermediate and final products were characterized with powder X-Ray diffraction, scanning electron microscopy and products, in addition, were characterized with transmission electron microscopy and elements mapping. Key words: high entropy carbides, carbothermal reduction, high temperature ceramics, sol-gel method,
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