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Structural changes in intermetallic compounds
Doležal, Petr ; Prchal, Jiří (advisor) ; Daniš, Stanislav (referee)
This diploma thesis is focused on the study of the structural phase transitions in intermetallic compounds LaPd2(Al,Ga)2 by low-temperature x-ray powder diffraction and macroscopic measurements on single crystals. The results obtained from powder diffraction at room temperature confirm that the compounds crystallize in tetragonal CaBe2Ge2 structure type (space group P4/nmm). At low temperature all the compounds undergo the same structural phase transition by lowering the symmetry to the orthorhombic space group Cmma. Although the structural transformation is of first order, the transition is not-manifested in step-like change of the phase at a certain temperature, but occurs in a broader temperature interval. In this interval the different phases coexist and transform gradually from high- to low- temperature phase. After application of hydrostatic pressure the structural transition is shifted to higher temperatures. Despite that the low temperature structures are of the same type, there is a difference between compounds containing Ga and Al in the discontinuity of the lattice parameters resulting in a distinct anomaly in electrical resistivity. In pressures >0.6 GPa this characteristic anomaly on single crystalline CePd2Al2 is changed, indicating a pressure- induced change of the low-temperature...
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CeT2Al2 compounds with enhanced electron-phonon interaction - preparation and characterisation of single crystalline samples
Mičková, Zuzana ; Doležal, Petr (advisor) ; Prchal, Jiří (referee)
This thesis is focused on preparation and characterisation of CePd2Al2, which is an intermetallic, incongruently melting compound. Due to its incongruent nature a number of polycrystalline samples was made to find an ideal nominal stoichiometry for a precursor for Czochralski growth of a single crystalline sample. Seven polycrystalline samples of different nominal stoichiometries were prepared in mono- arc furnace and studied via electron microscopy, differential scanning calorimetry and four of the samples also by powder diffraction. The result of analyses showed a presence of a hexagonal phase of stoichiometry 16.6:33.3:50 in multiple of the samples. This phase crystallizes at temperature higher than the rest of the present phases. The hexagonal phase was found to not occur in four of polycrystalline as-cast samples, namely of stoichiometries 22:40.7:37.3, 22:41.1:36.9, 22:41.5:36.5 and 22:42.5:35.5 atomic percent. The most suitable stoichiometry of the precursor for Czochralski growth of single crystalline sample in tri-arc furnace was found to be stoichiometry 22:41.1:36.9.
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Vibron states in cerium crystalline compounds
Doležal, Petr ; Javorský, Pavel (advisor) ; Detlefs, Blanka (referee) ; Rafaja, David (referee)
This thesis is focused on study of the vibron state in Ce intermetallics. The presence of a vibron state is a consequence of an enhanced magneto-elastic interaction, between phonons and 4f electrons of the Ce ion. The magneto-elastic interaction is usually weak and can be neglected, but here in CeAl2, CePd2Al2, CeCuAl3 and CeAuAl3 is considered to be strong enough, which leads to a bound state called the vibron state. A well determined crystal structure of these compounds is a necessary prerequisite to discuss this unique behaviour. Therefore our investigation is performed on the following levels: A crystal structure study of (Ce,La)Pd2Al2-xGax and CePt2Al2, by low temperature and high temperature X-ray powder diffraction; Investigation of bulk and transport properties of a CePt2Al2 single crystal using the specific heat, magnetisation and electrical resistivity measurements; Symmetry analysis of phonon modes and angular momentum operators in the model Hamiltonian, based on group theory; And finally the study of phonon dispersion curves in CePd2Al2 and LaPd2Al2 single crystals using inelastic X-ray scattering. All these results and preformed analyses lead to the following conclusions: The CePd2Al2 and LaPd2Al2 are incongruently melting phases. We found and described the way which has allowed us to...
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Determination of the functional volumes of the reservoir considering input data uncertainties
Paseka, Stanislav ; Doležal, Petr (referee) ; Szolgay,, Ján (referee) ; Marton, Daniel (advisor)
Damaging changes and interventions in the water cycle in our landscape caused mainly in the last century together with uncertainties from climate change are the cause of more frequent occurrences of hydrological extremes. In Hydrology, the most urgent problem is that the values of the long-term mean flows are decreasing in rivers as well as the yield of groundwater sources, but on the other hand, we cannot forget to the problem of extreme floods. In these consequences developing methods and tools to uncertainty analysis of the reservoir yield and of the reservoir flood protection is very important, useful and desired. The main aim was to determine the functional volumes of the reservoir considering input data measurement uncertainties and to quantify them and was explained how uncertainty took into account in results. The active storage capacity was determined from the historical series of monthly flows that were affected by uncertainties, next were applied on water evaporation, seepage losses of the dam and morphological volume-area curves. The simulation-optimization reservoir model was developed and temporal reliability as reservoir yield performance measures was applied. This model will extend the existing UNCE_RESERVOIR software. The flood capacity was determined from random flood wave variations were obtained by repeatedly generating uncertainty on the flood hydrograph. Software was developed based on the modified Klemes method, which was able to transform flood waves. The measurement uncertainties of data inputs were created using Monte Carlo method in both softwares. By connecting two softwares, the functional volumes of the reservoir under conditions of measurement uncertainties were complexly determined. The case study was applied to the real water reservoir, in the Morava River Basin. The result will be whether the dam is resistant to the current conditions, or the optimal design of the functional volumes of reservoir under conditions uncertainties.
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Structural changes in intermetallic compounds
Doležal, Petr ; Prchal, Jiří (advisor)
This diploma thesis is focused on the study of the structural phase transitions in intermetallic compounds LaPd2(Al,Ga)2 by low-temperature x-ray powder diffraction and macroscopic measurements on single crystals. The results obtained from powder diffraction at room temperature confirm that the compounds crystallize in tetragonal CaBe2Ge2 structure type (space group P4/nmm). At low temperature all the compounds undergo the same structural phase transition by lowering the symmetry to the orthorhombic space group Cmma. Although the structural transformation is of first order, the transition is not-manifested in step-like change of the phase at a certain temperature, but occurs in a broader temperature interval. In this interval the different phases coexist and transform gradually from high- to low- temperature phase. After application of hydrostatic pressure the structural transition is shifted to higher temperatures. Despite that the low temperature structures are of the same type, there is a difference between compounds containing Ga and Al in the discontinuity of the lattice parameters resulting in a distinct anomaly in electrical resistivity. In pressures >0.6 GPa this characteristic anomaly on single crystalline CePd2Al2 is changed, indicating a pressure- induced change of the low-temperature...
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Measurement of infiltration in the field using MiniDisk infiltrometer
Vláčilíková, Michaela ; Doležal, Ing Petr (referee) ; Kameníčková, Ivana (advisor)
The diploma thesis deals with measuring of infiltration by MiniDisk method and its evaluation, but also with analysis of intact and grab soil sample, by means of which it is possible to assess the soil quality. The measurements took place on 30.4.2019, 4.5.2019, 12.5.2019, 2.6.2019, 30.6.2019, 2.7.2019, 31.8.2019 and 21.9.2019 on grassland near the town of Luhačovice. Grab and intact soil samples were taken from the upper soil layer and processed in a pedological laboratory. The Zhang method was used to evaluate the infiltration results. The results of soil analyzes and infiltration were processed numerically, plotted and subsequently described and compared.
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