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Effect of moisture on the electrical properties of silicate composites
Karlíková, Helena ; Kusák, Ivo (referee) ; Rovnaník, Pavel (advisor)
This work deals with study on the dependence of electrical properties on the moisture content in silicate composites. The theoretical part contains information about the electrical properties of cement-based and alkali-activated binders, as well as knowledge on moisture parameters and the presence of moisture in the material structure. Samples of cement-based mortars and alkali-activated slag with a graphite powder in the range of 0–18 per cent by weight were produced and quartz sand was used as filler in the experimental part. The samples were provided with copper electrodes and saturated with water after hardening. The electrical properties of the mortars were monitored by means of impedance spectroscopy during the gradual drying of the samples. The effect of microstructure has been studied using scanning electron microscopy and mercury intrusion porosimetry. The results indicate that a significant increase in electrical resistance occurs only when the relative sorption humidity content is below 20 per cent in the 40–5000 Hz frequency range.
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Electrical, Optical and Sensoric Properties of Organic Semiconductors
Pochekailov, Sergii ; Zmeškal, Oldřich (referee) ; Nešpůrek, Stanislav (advisor)
There is big interest in cheap, sensitive and selective gas sensors. In this work, substituted soluble phthalocyanines are proposed as a sensing materials for several gases. Optical, electrical and gas sensing properties of several phthalocyanines were studied and the mechanisms of their interaction with several analyte gases are described. It was found, that sulfo-substituted Pcs has good sensitivity to humidity. Sulfonamide-substituted phthalocyanines are promising for nitrogen dioxide and volatile organic compounds detection. tert-Butyl-substituted phthalocyanines are sensitive to NO2 under higher temperature and seems to be used for environmental monitoring. Commercial gas sensors for NO2, ethanol and humidity were successfully created.
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Study of electric properties of nanocomposites
Libra, Miroslav ; Rozsívalová, Zdenka (referee) ; Polsterová, Helena (advisor)
The present master´s thesis deals with the electrical properties of nanocomposite materials. Samples for the experiment are made epoxi resin and oxides TiO2 and Al2O3 as nanofillers in different percent performace. The samples nanocomposites are measured temperature dependence of the resistivity inside, dissipation factor and relative permittivity. It discusses the effect of the filler on the resulting electrical properties of the polymer.
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Electrical and thermal characteristics of lead-free solder joints
Jurásek, Matěj ; Adámek, Martin (referee) ; Schnederle, Petr (advisor)
This wok is focused on the issue of soldering. The theoretical part describes the basic requirements for materials and solders alloys, which enter into this process. Further also factors that have a major impact on the quality of joints and methods, that are used for final testing of electrical and optical properties. The aim of the practical part of this work will be monitoring changes in electrical properties depending on the base material, surface finish PCB contact surfaces, the type of solder alloy and residual oxygen concentration in the atmosphere. The resulting values are compared, and they will draw the final recommendations for the method of soldering used alloys
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Processing and properties of piezo-dielectric ceramic composites
Kučera, Ondřej ; Drdlík, Daniel (referee) ; Maca, Karel (advisor)
The diploma thesis deals with piezoelectric materials combining dielectric and piezoelectric ceramics. The first part of this diploma thesis summarizes the preparation of ceramic materials and thermodynamic of sintering. The electric properties of ceramic materials and current knowledge in BCZT ceramics are summarized. The second part of this diploma thesis describes BCZT ceramics preparation process from raw materials in powder form through the reaction of the precursors to sintering the experimental material into the compact body. The properties of prepared BCZT samples such as density, grain size, hardness, relative permittivity, piezoelectric constant and dielectric loss are summarized in the thesis.
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Study of the influence of fillers and external conditions on the resistivity of cement composites
Kejda, Dalibor ; Melichar, Jindřich (referee) ; Černý, Vít (advisor)
The progress of new materials is important for the construction industry. Modern materials include cement composites with reduced resistivity. This is achieved by adding suitable electrically conductive fillers. If there is enough of these fillers, the so-called percolation threshold occurs. Suitable fillers (Condufit C4 and Supragraphite C300) have been proposed. Recipes have been designed to be before and after the percolation threshold. The tests were performed on beams measuring 40x40x160 mm with built-in electrodes for measuring their resistivity. The aim of the work was the research of influencing external conditions on cement composites. The effect of temperature was verified. The lowest values of resistivity were evaluated at temperatures of 50 ° C and the resistivity increased with decreasing temperature. The effect of humidity on the resistivity was then verified. Reference samples and samples with a smaller proportion of graphite powder showed larger differences in resistivities with increasing humidity. The samples above the percolation threshold were not much affected by increasing humidity. Finally, the effect of loading on the resistivity of the samples was verified. Almost all samples with increasing compressive stress showed an increasing value of resistivity.
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Novel materials for organic and hybrid electronics and photonics
Kratochvíl, Matouš ; Yumusak,, Cigdem (referee) ; Táborský, Petr (referee) ; Weiter, Martin (advisor)
Obor organické elektroniky nabízí jedinečnou možnost masové výroby levné a ekologicky přívětivé elektroniky. Otevírá dveře novým funkcím a tvarům zařízení, které standardní elektronika na bázi kovu a křemíku neumožňuje Možnosti dané povahou organických látek a pokrok ve výzkumu syntézy nás zásobují novými materiály pro fotonické aplikace. Hlavní motivací této práce je hledání nových materiálů a zkoumání vztahu mezi jejich molekulární (a krystalickou) strukturou a vlastnostmi. Tato práce je zaměřena na studium optických a/nebo elektrických vlastností nových materiálů pro fotonické aplikace. Materiály prezentované v práci jsou organické i hybridní organicko-anorganické, u nichž je snaha získat to nejlepší z obou světů. Výzkum prezentovaný v této práci se skládá ze tří samostatných částí, které jsou propojeny cílem studovat vztah mezi strukturou materiálu a jeho vlastnostmi a metodami používanými ke studiu těchto vlastností. První část si klade za cíl představit materiály vykazující účinnou fluorescenci v pevné fázi (Solid-State Fluorescence, SSF). V této práci jsou prezentovány dvě série materiálů vykazujících SSF. Barva emise je řízena změnami skupin přitahujících elektrony v push-pull systémech molekul. Výsledky ukazují efektivní (>10%) emise pokrývající většinu viditelného spektra (~450–650 nm). Druhá část prezentovaného výzkumu zkoumá vliv thionace na známou skupinu nízkomolekulárních polovodičů – diketopyrrolopyrrolů (DPP). Prezentované výsledky ukazují ve studovaných molekulách výraznou preferenci n-typové chování následkem thionace, s řádovým zvýšením pohyblivosti elektronů, a také působivě nízko ležící hladiny LUMO (~ 4,5 eV). Třetí část uvedených výsledků je zaměřena na perovskitové materiály pro fotonické aplikace. Hybridní materiál – organo-olovnato-halogenidový perovskit je již téměř půldruhého desetiletí v centru pozornosti výzkumníků v oblasti pokročilé fotoniky. Perovskitové solární články prokazují pozoruhodnou účinnost, avšak jejich využití stále brání problémy se stabilitou. V této práci je prezentována studie stability jako referenční bod pro další výzkum v této oblasti a pro získání vhledu do procesů ovlivňujících stabilitu perovskitových materiálů a solárních článků. Následně je navržen a otestován přístup ke zvýšení stability a výkonu článků, využívající materiály studované ve druhé studii.
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Study of Electric and Thermal Properties of Building Materials with Conductive Additives
Veselá, Jana ; Krouská, Jitka (referee) ; Zmeškal, Oldřich (advisor)
This work focuses on study of electric, dielectric and thermal properties of composite electrically conductive building materials composed of magnesium oxychloride cement and small amount of graphene and graphite admixtures. The aim of this work was to determine thermal properties of materials and create a model of electric current conduction mechanism in material. Electric and dielectric properties were determined with using of transient direct current measurement of resistivity and impedance spectroscopy. Thermal properties were investigated using transient step-wise method and fractal analysis of thermocamera data. Electrical resistivities of materials are determined from the direct current measurements. Model of transport of electrical charge carriers was evaluated by fitting impedance data to an equivalent electrical circuit model. Thermal conductivities and thermal capacities were determined by means of thermal measurements. The presented properties for example can be used for assessment of suitability for specific construction applications.
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Study of Electric Properties of Electrochemical Transistors with Ionic Liquids
Blahut, Jan ; Pospíšil, Jan (referee) ; Zmeškal, Oldřich (advisor)
This bachelor’s thesis is focused on preparation of organic electrochemical transistors and following characterization of electric properties of these systems. Two types of electrode systems were used for preparation – glass substrates with steamed oxide of indium and tin and polylactic acid substrates with admixture of carbon soot. Three methods were tested for creation of PEDOT channel. Materiál printing, spin-coating and manual application. The measurement shows, that voltage applied to gate electrode has no effect switching of transistor. Size and polarity of current between source and drain electrodes has a major influence here.
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