Daniel Michalik

The Origin of the Ferroelectricity in the Bismuth Titanate Bi4Ti3O12 with Perovskite-Like Layered Structure

The goal of this study was to investigate the origin of ferroelectricity in Bi4Ti3O12. The bismuth titanate Bi4Ti3O12 (BTO), which belongs to the Aurivillius family, is one of the most interesting compounds among the bismuth-based layered ceramics. BTO is a ferroelectric material with wide applications in the electronic industry, as capacitors, transducers, memory devices and sensors. Aurivillius structures are described with a general formula following form:Am-1Bi2BmO3m-1. BTO ceramic materials is an Aurivillius structure with m = 3. This ceramic materials were prepared by conventional mixed-oxide method of the solid state reaction. The temperature of the Bi4Ti3O12 sintering was selected on basis of thermogravimetric studies. The crystal structure of Bi4Ti3O12 was examined at room temperature with an X-ray diffraction method. Phase formation behavior was investigated using the differential thermal analysis (DTA) and the thermal gravimetric (TG). The microstructure was investigated by SEM method. Based on the Dorrian’s model, the value of displacements between bismuth ions and oxygen octahedra was calculated.

Influence of m and n Parameters of Ca-α-Sialon: Eu Solid Solution on Phosphor’s Optical Properties

Ca-α-sialon doped by Eu2+ is a promising material for white LED phosphors due to the strong UV absorption and a yellow broad band emission of activator. The general formula of α sialon enables changing matrix composition by altering m (Al-N) and n (Al-O) parameters of cross-substitution. Changes of the neighboring Eu ligands in the host crystal lattice would trigger important modification of the photoluminescence properties because of different crystal field splitting and the energy of the d orbital. The aim of this study was to correlate the matrix solid solution parameters with photoluminescence spectra features. The specimens of Ca-α-sialon:Eu2+ with m, n parameters in the range of 0.5-2.5 and 0.25-1.25 respectively, were prepared by the solid state reaction method in the reducing atmosphere of a graphite furnace. The phase composition of the obtained specimens was characterized by XRD, microstructure and morphology by the SEM/EDS techniques. The photoluminescence spectra (excitation, emission) were also recorded. Results show that m/n parameters have a significant influence on the final optical properties.

Preparation of translucent YAG:Ce ceramics by reaction sintering

The paper presents preparation of YAG precursor powders mixture with ability for the reaction sintering at lower temperature. The powder mixture was mechanochemically processed and characterized for the specific surface area and crystallinity (XRD). Sintering experiments were performed on the batched powders, mechanochemically processed powders and as-synthesised YAG powders. XRD measurements and SEM/TEM studies were applied for characterization of the phase composition and development of YAG ceramics. Transmittance of the resultant ceramics was measured. It has been shown that YAG structure formed at 200 ?C lower temperature in comparison to the reference specimen and contamination by the side phases (YAM, YAP) was limited. The best translucency was achieved for the reaction sintering of the mechanochemically processed powders.

Manufacturing of Light Weight Aggregates from the Local Waste Materials for Application in the Building Concrete

The aim of those research was to find out the technique of the car windshield glass waste utilization. The research was performed in cooperation with the Polish small company, active in the waste utilization. Manufacturing of the light weight aggregates (LWAs) for application in the building concrete has been chosen as an appropriate solution. The local coal mine slates, the fine-grained coal mine wastes and fly ash from the local power station were tried for making the suitable mixture for granulation and sintering. All waste materials were characterized for their granulation, chemical composition and thermal behavior (DTA, TG/DTG, linear changes). Several mixtures with various composition were prepared, milled, homogenized and pelletized with water addition and finally sintered at 950°C. Thermally treated granules were tested for their density, porosity and mechanical properties. Some specimens were observed in scanning microscope. It has been shown that by variation of the composition of the waste materials it is possible to produce aggregates with a large variety of mechanical properties and porosities.

The influence of charge compensation defects on the spectroscopic properties of europium doped Ca9Y(PO4)7

In this study, a series of Ca9Y(PO4)7 compounds doped with 5% of Eu ions and with different [Y]/[Ca] ratios was synthesized using the Pechini method. Due to the presence of two different cations in the studied matrix (Ca2+ and Y3+) that are available for europium substitution, the synthesis parameters were selected to obtain the incorporation of the europium ions (5% mol) into the calcium sites only. The phase composition as well as elemental analysis and the spectroscopic measurements, carried out before and/or after the reduction of Eu3+ were performed to characterize the obtained phosphors. The XRD patterns show that in all cases the obtained materials consist of pure phase of Ca9Y(PO4)7. PLE and PL spectra measured before the reduction indicate that for the materials with the excess of yttrium, an additional Eu3+ site is observed which was not observed for materials with a deficiency of yttrium. For samples obtained after the reduction, the luminescence of Eu2+ depends on the changes of the Y/Ca ratio. The observed differences in Eu2+ luminescence are discussed taking into account the creation of different compensation defects depending on change of the Y/Ca ratio.

Engineering of Synthesis of Eu,Ca-α-Sialon Phosphor via the Solid-Liquid Synthesis

The aim of this research was to find out the way of the synthesis temperature reduction without deterioration of the phosphors optical properties. Since crystallization of Eu,Ca-α-sialon occurs by means of sialon crystallization from the oversaturated oxynitride liquid, thus a rise of the liquid phase amount could be performed not only via an increase of temperature but also through the application of the low eutectic additives. Al2O3 and AlF3 additives have been chosen as the sources of liquid at the reaction temperature. The syntheses were carried out in a graphite furnace at 1650°C and the powders were characterized for their phase composition, particles morphology, excitation and emission properties and their quantum yield of luminescence was compared. It has been found that alumina addition to the initial mixture of nitrides was the most effective in formation of sialon solid solution with a minor contamination with AlN. Emission intensity of sialon phosphor was doubled if they were synthesized with each of additives. Quantum yield of tested phosphors was over 0.85 if excited at 380 nm for alumina and similar for AlF3 modified composition. A significant particles refinement was observed if AlF3 was applied.

The Role of Aluminium Source (Al2O3/AlN) in the Synthesis of the Ca-α-SiAlON:Eu2+ Phosphor

The purpose of the presented research was to compare the effect of changing the aluminium source in the mixture of initial powders on the properties of the final phosphor powder of Ca – α-SiAlON doped with Eu2+. The phosphor composition was designed as Eu0,048Ca0,752Si9,6Al2,4O0,8N15,2 and it was prepared by the solid state reaction in a temperature range of 1450-1650 °C. AlN and/or η-Al2O3 powders were used as a source of aluminium. It has been found that presence of aluminium nitride or oxide in the mixture of initial materials significantly changed the course of α-sialon formation, chemical composition of that solid solution and the resultant photoluminescence properties. It has been established that a small amount of η-Al2O3 with a suitable carbon addition was profitable for liquid formation and enhanced crystallization of Ca,Eu-α-sialon. The excessive oxide-rich liquid at reaction temperature led to sintering of phosphor particles and decreased emission intensity while lack of sufficient amount of liquid (nitrogen-rich starting composition) resulted in AlN presence and considerably reduced emission intensity of this phosphor.

Wpływ parametrów mielenia wysokoenergetycznego na właściwości proszków kompozytowych aluminiowo-ceramicznych

Drobnoziarniste kompozyty na osnowie aluminium i jego stopów, wzmacniane cząstkami ceramicznymi stanowią alternatywę dla kompozytów otrzymywanych metodami odlewniczymi, jeśli dąży się do submikroskopowego stopnia rozdrobnienia. Celem prezentowanych badań było określenie wpływu parametrów mielenia w młynie planetarnym na efekty i właściwości proszku kompozytowego na osnowie siluminu z dodatkiem azotku krzemu i węgla szklistego. Analizowane parametry mielenia to: czas mielenia, prędkość obrotowa, średnica mielników, materiał wyłożenia oraz średnica misy mielącej. Zastosowano metody badawcze umożliwiające określenie rozkładu ziarnowego proszku kompozytowego, powierzchni właściwej, stopnia utlenienia aluminium i azotku krzemu oraz składu fazowego.

Synthesis and Optical Characterization of M-α-Sialon (M=Ca, Ba, Sr) Doped by Europium

Oxynitrides compounds are interesting for white LED industry because more covalent matrixs bonds in comparison to oxides enable to obtain higher color temperature of wLED. The Sialons luminescence material doped by rare earth ions with high mechanical and chemical resistance and a broad emission band may become an alternative for garnet phosphors. The goal of the study was to investigate influence of divalent stabilizing cations on luminescence properties of M-α-Sialon doped with Eu2+ in order to estimate its potential for YAG:Ce replacement in WLEDs. The compound of general formula EuxM1-xSi9,6Al2,4O0,8N15,2, where M=Ca, Ba, Sr, was prepared by the solid state reaction method from the mixture of the relevant oxides, nitrides and carbonates. Synthesis was carried out at the temperature of 1650°C for 4 h in a reduction atmosphere (N2+CO). The structure and morphology of obtained powders were analyzed by XRD and SEM/EDS methods, respectively. Optical properties were investigated by excitation, emission and reflection spectra and compared to photoluminescence properties of standard YAG:Ce. The obtained specimens show the significant effect of synthesis parameters on the phase composition and intensity of emission of M-α-Sialon:Eu2+ powder.

Preparation and Characterization of Al-Si3N4 Composite Particles

Fine Al-Si3N4 composite particles were prepared via mechanochemical processing of the coarse aluminum powder and submicron silicon nitride powder in order to obtain the core-shell structure of composite powder particles. It was expected that soft aluminum particles could form a thin coat on hard silicon nitride particles. The resultant particles were characterized through scanning and transmission electron microscopy and electron spectroscopes. Their particle size distribution, specific surface area, nitrogen/oxygen content and phase composition were also determined. Chemical analysis showed that limited oxidation occurred during mechanochemical processing. It has been found that a thin Al-enriched layer (larger than 10 nm) formed at some Si3N4 particles apart from the opposite effect if Si3N4 particles were occluded in coarser Al items. Discussion of the results is also presented.