Ceramic materials are natural or synthetic, inorganic, non-metallic materials incorporating ionic and covalent bonding. Most ceramics in use are polycrystalline materials where grains are connected by a network of solid-solid interfaces called grain boundaries. The structure of the grain boundaries and their arrangement play a key role in determining materials properties. Developing a fundamental understanding of the formation, structure, migration and methods of control grain boundaries have drawn the interest of scientists for over a century.<br> While grain boundaries were initially treated as isotropic, advances in materials science has expanded to include energetically anisotropic boundaries. The orientation and structure of a grain boundary, determined by this anisotropy, controls the mobility of a grain boundary. The mobility is the controlling factor during grain growth impacting the microstructural evolution of a material.<br> This thesis covers fundamental research to model how a materials’ equilibrium crystal shape can be used as a grain growth control mechanism. First an overview of ceramic processing and microstructural development is presented with a focus on the role of grain boundaries in determining the properties of a material. The role of anisotropy and related recent work is highlighted setting the foundation for the link between the equilibrium crystal shape and grain growth. A discussion on the selection of the NiO-MgO system for all experimental work is included.<br> A novel production and processing route for NiO-MgO was developed. Mechanical alloying and milling resulted in significant impurity contamination therefore a chemical production route was used. A modified amorphous citrate process was developed where metal salts containing Ni and Mg were mixed with a polyfunctional organic acid. Rapid dehydration and calcination at 500°C resulted in chemically homogeneous powders. The amorphous citrate production route produced powder with crystallites ranging from 244-393 nm and agglomerates ranging from 20-300 μm with plate-like morphology.<br> NiO-MgO powders produced via the amorphous citrate method were sintered using various techniques. Conventional sintering was unable to produce fully dense samples peaking with relative densities from 95-96%. The introduction of pressure through spark plasma sintering and hot pressing improved the relative sample density to 97-100%. It was discovered that exposure to the vacuum required for spark plasma sintering and hot pressing resulted in the reduction of NiO. Spark plasma sintering created oxygen depleted regions and hot pressing further reduced NiO to pure nickel metal which precipitated out at the grain boundaries.<br> Due to the poor sintering behavior of NiO-MgO grain growth experiments were carried out on the large agglomerates formed during the amorphous citrate process. Agglomerates with more than 50 grains with a thickness of at least 1 μm were selected. Grain growth was measured across five compositions with Ni:Mg ratios of 100:0, 75:25, 50:50, 25:75, 0:100. The average grain size and growth rate increased with increasing nickel content with a significant jump between 50% and 75%. Increasing nickel content was also observed to correspond with a higher number of grains exhibiting surface faceting.<br> The NiO-MgO equilibrium crystal shape as a function of composition was measured previously. To make the equilibrium crystal shape a more viable control for grain growth a quantitative microstructural characterization technique was developed to measure a materials equilibrium crystal shape. Topographic surface information (surface facets measured by atomic force microscopy, AFM) and grain crystallographic orientation (measured by electron back-scattered diffraction, EBSD) were combined to produce the crystallographic topography of a sample surface. Surface crystallographic topography was used to identify the faceting behavior of grains with a range of orientations. Using the combined data, facet stability maps (n diagrams) for NiO-MgO were developed.<br> Controlling grain growth via the equilibrium crystal shape offers the potential to produce microstructures with a high frequency of desirable grain boundaries (grain boundary engineering) and therefore properties. The combination of using AFM and EBSD to create crystallographic topographical surface data and n-diagrams has been demonstrated. N-diagrams for most materials do not exist, but the technique used here can be applied to a wide range of materials and will expand the ability to control microstructures of ceramic materials.<br><br>

Pulsed LASER deposition (PLD) is widely recognized as excellent deposition technique owing to stoichiometric transfer of target material, easy preparation and high quality. Thin films from few nanometers to micrometer regime can be fabricated with equal ease. Although a batch process is not suitable for mass scale industrial production, PLD is a versatile technique, efficient and convenient for high quality basic research.  This thesis illustrates the use of PLD technique to study the emerging trends in tailoring multifunctional magnetic thin films both from basic nanoscience and device development point of view.      After a comprehensive review of magnetism in chapter 1: entitled ‘A journey through classical to modern trends in magnetism, and multifunctional thin film devices’ followed by a reasonably thorough discussion on Pulsed Laser thin film technique in Chapter 2, we present: Studies of tailoring composite high energy product permanent magnetic FePtB based thin films for applications in NEMS /MEMS, (Chapter 3). Study of search for new multiferroic materials by investigating the properties of Chromites. Crystalline Chromites are antiferromagnetic below 150oC.  However depositing thin films by PLD of the crystalline 95.5% dense targets produced by Surface Plasma Sintering, we discovered that the resulting films were amorphous and ferromagnetic beyond room temperature. Moreover advanced spectroscopic techniques revealed that the amorphized state is metallic with Cr in a mixed valence state.   An understanding of the underlying physics of the observed phenomenon has been carried out based on first principles calculations.  These results are now being considered for publication in a high profile journal.  Extensive studies on the films showing that these materials are ferromagnetic, but not ferroelectric are discussed in chapter 4. A preliminary presentation of these studies was pier reviewed and published in MRS symposium proceedings. Fabrication of Room temperature, Transparent, high moment soft ferromagnetic amorphous Bulk metallic glass based FeBNbY thin films by PLD, suitable for Nanolithography in NEMS/MEMS device development .  (Chapter 5) From a basic study point of view on new trends on magnetism we present: 4. The use of PLD technique to demonstrate room temperature ferromagnetism in undoped MgO, and V-doped MgO thin films.  Both of these oxides which do not contain any intrinsically magnetic elements and are diamagnetic in their bulk form belong to a new class of magnetic films, the so called d0magnets signifying that robust above room temperature ferromagnetism arising from defects and controlled carriers and no occupied d-states can be tailored in semiconductors and insulators.  These, mostly ZnO and MgO based thin films which may be classified as Dilute Magnetic Semiconductors, DMS, and Dilute Magnetic Insulators, DMI, are now the materials of active interest in future Electronics involving components which exploit both charge and spin of electrons in the arena of SPINTRONICS. Extensive characterization of magnetic, electrical, optical properties and microscopic structure has ensured development of high quality magnetic materials for future applications. Further research on these promising materials is expected to yield new generation spintronic devices for better performance in terms of efficiency, energy consumption and miniaturization of sizes. / QC 20120511

The specific surface area reduction and pore size distribution coupled with N2 adsorption-desorption hysteresis isotherm were studied in the temperature range of 1400-1550¢J for periclase MgO powder having 0.1£gm in size and with face-centered cubic structure. The apparent activation energy of such a rapid coarsening-coalescence process for MgO powder was estimated as 181¡Ó3kJ/mol. The minimum temperature for sintering/coarsening/coalescence of submicron MgO particles was estimated to be near 1300¢J based on the extrapolation of steady specific surface area reduction rates to zero. Pulsed laser ablation (PLA) of periclase MgO powders in water was conducted under Q-switch mode and specified water height and water depth (10 mm) for an accumulation time of 5 and 20 minutes at 10 Hz. Such a PLA process has successfully synthesized nanosized and protonated MgO particles from Mg(OH)2 and lamellar precusors, implying the three phases may co-exist at high pressure and temperature conditions upon dynamic shock loading. A significant internal compressive stress up to 10 GPa was built up for the MgO but not the readily relaxed Mg(OH)2 nanocondensates. The lamellae-derived Mg(OH)2 tended to undergo a dehydroxylation process to become MgO following a specific crystallographic relationship, i.e. lamellar basal layer parallel to Mg(OH)2(0001) and MgO(111). The minimum band gap of the colloidal solution of MgO/Mg(OH)2/lamellae was lowered to ca. 5.2eV after the PLA process.

In part I, MgO and Co1-xO powders in 9:1 and 1:9 molar ratio (denoted as M9C1 and M1C9 respectively) were sintered and homogenized at 1600oC followed by annealing at 850 and 800oC, respectively to form defect clusters and precipitates. Analytical electron microscopic (AEM) observations indicated the protoxide remained as rock salt structure with complicated planar diffraction contrast for M9C1 sample, however with spinel paracrystal precipitated from the M1C9 sample due to the assembly of charge- and volume-compensating defects of the 4:1 type, i.e. four octahedral vacant sites surrounding one Co3+-filled tetrahedral interstitial site. The spacing of such defect clusters is 4.5 times the lattice spacing of the average spinel structure of Mg-doped Co3-dO4, indicating a higher defect cluster concentration than undoped Co3-dO4. The {111} faulting of Mg-doped Co3-dO4/Co1-xO in the annealed M1C9 sample implies the possible presence of zinc blend-type defect clusters with cation vacancies assembled along oxygen close packed (111) plane. In part II, the Mg2TiO4/MgO composites prepared by reactive sintering MgO and TiO2 powders (9:1 molar ratio) at 1600oC and then air-cooled or further aged at 900oC were studied by X-ray diffraction and (AEM) in order to characterize the microstructures and formation mechanism of nanosized Mg2TiO4 spinel precipitated from Ti-doped MgO. Expulsion of Ti4+ during cooling caused the formation of (001)-specific G.P. zone under the influence of thermal/sintering stress and then the spinel precipitates, which were about 30 nm in size and nearly spherical with {111} and {100} facets to minimize coherency strain energy and surface energy. Secondary nano-size spinel was precipitated and became site saturated during aging at 900oC, leaving a precipitate free zone at the grain boundaries of Ti-doped MgO. The intergranular spinel became progressively Ti-richer upon aging 900oC and showed <110>-specific diffuse scatter intensity likely due to short range ordering and/or onset decomposition. In part III, the Co1-xO/Co2TiO4 composite prepared by reactive sintering CoO and TiO2 powders (9:1 molar ratio) at 1450oC and then air-cooled were studied by X-ray diffraction and AEM in order to characterize the microstructures and formation mechanism of nanosized Co2TiO4 spinel precipitated from Ti-doped Co1-xO. Slight expulsion of Ti4+ during cooling caused the precipitation of nanosize Co2TiO4 spinel. Bulk site saturation also caused impingement of the Co2TiO4 precipitates upon growth. The Co3-dO4 spinel, as an oxidatin product of Co1-xO, was found to form at free surface and the Co1-xO/Co2TiO4 interface. The Co2TiO4 spinel particles formed by reactive sintering rather than precipitation were able to detach from the Co1-xO grain boundaries to reach parallel epitaxial orientation with respect to the host Co1-xO grains via Brownian-type rotation of the embedded particles. In part IV, AEM was used to study the defect microstructures of Zr-dissolved TiO2 prepared via reactive sintering the ZrO2 and TiO2 powders (8:92 in molar ratio, designated as Z8T92) at 1600oC for 24 h and then aged at 900oC for 2-200 h in air. The Zr-dissolved TiO2 with rutile structure showed dislocation arrays, defect clusters, G.P. zone, superlattice, nanometer-size domains incommensurate and commensurate superstructure, may be the precursor of ZrTi2O6 precipitates at 900oC. The rutile showed diffuse diffractions along [001] direction as a result of Zr4+ substitution for Ti4+ with volume compensating defect clusters. Incommensurate and commensurate structures, as indicated by diffraction splitting and extra diffraction along <100> and <010> directions may be attributed to the ordering and clustering process of Zr and Ti atoms in these directions. Part V, deals with the reactive sintering of ZrO2 and TiO2 powders (1:4 molar ratio) at 1400 to 1600oC in air to form orthorhombic ZrTiO4 (a-PbO2-type structure, denoted as a) and to study its epitaxial reorientation in the matrix of tetragonal TiO2 (rutile) grains with Zr4+ (15 mol %) dissolution. The epitaxial relationship of intragranular ZrTiO4 and Zr-dissolved rutile (denoted as r) was determined by electron diffraction as [010]a//[011]r; (001)a // (011)r (i.e. [100]a // [100]r; (001)a // (011)r). The reorientation of the intragranular particles in the composites can be reasonably explained by rotation of the nonepitaxial particles above a critical temperature (T/Tm > 0.8) and below a critical particle size for anchorage release at interface with respect to the host grain. Reactive sintering facilitated the reoreientation process for the particles about to detach from the grain boundaries. The Brownian rotation of the confined ZrTiO4 particles in rutile grains was activated by a beneficial lower interfacial energy for the epitaxial relationship, typically forming lath-like ZrTiO4 with (101)a/(211)r habit plane having fair match of oxygen atoms at the interface. Further aging at 900oC for 50 h in air caused modulated and periodic antiphase domains in ZrTiO4 matrix, as likely precursor of equilibrium ZrTi2O6.

The synchronously pumped femtosecond optical parametric oscillator (OPO) based on was periodically poled 5-mol.% MgO-doped lithuium niobate was demonstrated by means of non-critical quasi phase matching. The femtosecond OPO is cable of operating at room temperature and shows no photorefractive damage. The spectrum can be tuned by varying the cavity length up to 70 £gm, the temperature of the nonlinear crystal from room temperature to 150¢J, and the grating periods. The cavity was designed to resonate at 1.33 £gm with bandwidth of 100 nm. The maximum output intensity of the signal is 43 mW with TEM00 mode. The signal slope efficiency is 11%. The spectrum range of the idler is tunable from 1.8 to 2.8 £gm.

Recognising that the characterisation of actual interfaces in magnetic multilayer systems will provide valuable insight for the integration of spintronics in practical devices, a study of interface effects in various structures is presented. Magnetometry measurements are performed for a range of Fe thicknesses (0.4 - 23 nm) grown by molecular beam epitaxy on GaAs and InAs substrates in order to determine the factors governing the evolution of the magnetic moment of epitaxial Fe grown on a zinc-blende semiconductor. A greater reduction of the Fe magnetic moment is observed for films grown on InAs as compared to GaAs, as the Fe films reach a bulk-like moment (within 10% deviation) at a thickness of ~5.2 nm and ~2.2 nm, respectively. From this direct comparative study it is concluded that interface and interdiffusion effects are the dominant mechanisms influencing the value of the magnetic moment for ultra-thin Fe films on GaAs and InAs. Spin injection at this interface is performed, by detecting optical polarisation in the oblique Hanle geometry from a Fe/AlGaAs/GaAs spin-light emitting diode structure. The electrical and magnetic properties of the system are presented, and a ~1% injection polarisation at room temperature, rising to ~4% at 77 K is reported. A study of the deposition and growth of MgO thin (3 - 39 nm) films in conjunction with magnetic layers is also performed. Crystallinity of MgO grown on GaAs is obtained, and epitaxial growth of Fe and Co on MgO is demonstrated. Polarised neutron reflectivity results again indicate a slight decrease in Fe and Co magnetic moments due to interfacial oxide layers. MgO is also incorporated in a pseudo-spin-valve structure which demonstrates epitaxy-induced magneto-crystalline anisotropy. It is concluded that the interface quality is a critical parameter for spintronic devices. Atomic-scale defects and intermixing in real samples mean that current theoretical estimates of ~100% injection efficiency in perfect systems remain unattainable. However by increasing atomic-level structural control of interfaces, a substantial increase in efficiency might be achieved, similarly to the recent breakthrough in tunnelling magneto-resistance ratios which have reached 1000%.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14614号 / 工博第3082号 / 新制||工||1459(附属図書館) / 26966 / UT51-2009-D326 / 京都大学大学院工学研究科精密工学専攻 / (主査)教授 井手 亜里, 教授 木村 健二, 教授 藤田 静雄 / 学位規則第4条第1項該当

På Norrvattens reningsverk, Görvälnverket, produceras dricksvatten genom rening av råvatten från Östra Mälaren. Dricksvattenverket ligger i direkt anslutning till Mälaren, vilket är bra då vattnet inte behöver transporteras för att renas. Mälaren är Sveriges största dricksvattentäkt, men den är också mycket trafikerad av både fartyg och fritidsbåtar. På grund av all trafik finns det en risk att det sker oljeutsläpp om en olycka skulle ske. Oljeprodukter kan ge vattnet en motbjudande lukt. Detta gör att det producerade dricksvattnet enligt Livsmedelsverket anses som otjänligt, dvs. det bör inte användas som dricksvatten. Därför ville Norrvatten kartlägga vilka marina bränslen som används idag men också undersöka hur mycket pulveriserat aktivt kol (PAK) som krävs för att rena vattnet från bränslelukt. Detta för att vara beredda vid ett eventuellt utsläpp och då kunna tillsätta rätt mängd PAK. Detta undersöktes både genom en litteraturstudie och småskaliga laboratorieförsök där lukttröskel och rening med PAK undersöktes. Försöken analyserades med hjälp av luktanalyser, som utfördes av Görvälnverkets laboratoriepersonal. En litteraturstudie visade att de vanligaste marina bränslena idag för fritidsbåtar och fartyg är bensin respektive marin gasolja (MGO). Det är dessa två bränslen som använts vid försöken med pulveriserat aktivt kol. Planen från början var även att hybridolja skulle undersökas, men eftersom den betedde sig annorlunda i vatten jämfört med de övriga bränslena uteslöts den från vidare försök. Lukttröskelförsöket som gjordes för MGO visade att alla prov antingen luktade eller inte luktade så därför kunde ingen lukttröskel anges. Resultatet för vatten förorenat av bensin med en koncentration på 200 μg/l visade att det krävs 30 mg PAK/l för att eliminera bränslelukten från vattnet. Koncentrationen på 200 μg/l användes då det anses vara den högsta halt som skulle kunna nå Görvälnverket vid ett eventuellt oljeutsläpp. Dessvärre gav reningsförsöken med MGO inget konkret resultat. Detta eftersom lösligheten för MGO var felaktigt antagen och därför var koncentration av MGO löst i vatten okänd. De koncentrationer som undersöktes var därför total mängd tillsatt MGO i vattnet. Den slutsats som ändå kan dras från reningsförsöken med MGO är att PAK fungerar bra för att reducera bränslelukt, men att det krävs ytterligare försök. Det resultat man kan utgå från vid fortsatta undersökningar är att det krävs mer än 40 mg PAK/l för att rena förorenat vatten med en koncentration på 4 360 μg MGO/l samt mer än 60 mg PAK/l vid en koncentration på 8 720 μg MGO/l. / At Norrvatten’s treatment plant, Görvälnverket, drinking water is produced by purification of water from Mälaren. Mälaren is Sweden's largest source of drinking water, but it’s also heavily trafficked by commercial ships as well as private boats. Due to all traffic, there is a risk that oil spills will occur in the event of an accident. Oil products can give the water disgusting odor. This, according to Livsmedelsverket makes the produced drinking water unfit to be used as drinking water. Therefore, Norrvatten wanted to identify which marine fuels that are used today, but also to investigate how much powdered activated carbon (PAC) is needed to purify the water from fuel odor. This was investigated through a literature study and additional laboratory scale experiments where the relation between the odor threshold and the purification with PAC was investigated. The laboratory experiments were analyzed by using odor analyzes, where lab staff at the Görvälnverket smelled the samples and indicated how each individual sample smelled. Through the literature study it was found that the most common marine fuels today for private boats and commercial ships are gasoline and marine gas oil (MGO). These are the two fuels used in the experiments with powdered activated carbon. The plan was also to investigate hybrid oil. But since it behaved differently in water compared to the other fuels, it was excluded from further experiments. The odor threshold experiment made for MGO unfortunately showed that all samples either smelled or did not smell. Hence, no odor threshold could be specified. For water contaminated with gasoline at a concentration of 200 μg/L, 30 mg of PAC/L was required to eliminate the fuel odor from the water. The concentration of 200 μg/L was used since it is considered to be the highest level that may reach the Görvälnverket in the event of an oil spill. Unfortunately, the purification attempts with MGO produced no actual results. This was because the solubility of MGO was incorrectly assumed and therefore the concentration of MGO dissolved in water could not be obtained. The concentrations investigated were therefore the total amount of MGO added to the water. The conclusion that can still be drawn from the purification attempts with MGO is that PAC works well to reduce fuel odor. A result that can be the basis for future studies is that more than 40 mg PAC/L is required to purify contaminated water with a concentration of 4 360 μg MGO/L and more than 60 mg PAC/L at a concentration of 8 720 μg MGO/L.

Using different precursors, two series of nano Pt/MgO catalysts (Pt-II and Pt-IV, respectively) loaded with Pt in a wide range from 0.1 wt% to 2.2 wt% were prepared by using wet impregnation methods. The physico-chemical properties of catalysts were characterized by using BET, XRD, TPD-CO2, and other techniques. The results revealed that the precursor and content of Pt, especially the acid/base properties of the precursor solution, had a big influence on the structure, and surface properties of the catalysts. The loaded Pt is in metallic state in all the catalysts calcined at 1073 K. The Pt-II catalysts had larger surface areas and relatively narrow pore size distribution range. The MgO crystals in the calcined Pt-II-3 catalyst had more regular structure than that in the calcined Pt-IV-3 catalyst.

<p>In this work a flow stabilized corona torch plasma was used for periodic domain inversion of MgO-doped lithium niobate with 19 .1 μm periodic gratings. The effective non-linear coefficient (derr) achieved through corona discharge poling was 17.5 pm/V, which agrees well with theoretical value of 16~19 pm/V. By analysing the second harmonic generation (SHG) tuning curves, the grating uniformity over the 10 mm grating was investigated. The 0.6 run bandwidth of the SHG tuning at full width half maximum (FWHM) corresponded exactly to the theoretical value. The agreement between experimental data and theoretical results imply that the obtained periodically poled lithium niobate (PPLN) has high quality. By controlling temperature in the range of 20 °C to 120 °C tunability of SHG wavelength was demonstrated between 782 run and 788 run.</p> <p>Discharge characteristics of the corona were studied using a floating potential double probe and optical emission spectroscopy. Using the double probe the distribution of ion density downstream of the corona torch was observed. The maximum ion density of 2 x 1018 (ions/cm3) was achieved 2 mm below the discharge electrode. Measurement of the optical emission spectrum was used to determine the vibrational ion temperature to be 3953 K. The observed spectrum consisted entirely of the second positive band of nitrogen.</p> <p>The applied voltage range of 9 kV to 10 kV was observed to be optimum for domain growth in periodic poling. Poling uniformity of the 12 mm grating was optimized for an electrode to crystal spacing of 13 mm. Increasing the crystal temperature during poling reduces the required coercive field for domain inversion. This reduces the required applied voltage and also reduces the required poling time by increasing the domain-switching rate. Proton exchange pretreatment of the (+z) crystal surface prior to poling has been demonstrated to control domain spreading, however future efforts are required to ensure a more reliable nucleation condition. Both high vacuum and spin coated photoresist function to increase electrical discrimination of anode grating and provide an improved nucleation condition for periodic poling of MgO-doped lithium niobate. Poling uniformity of the 12 mm grating was optimised for an electrode to crystal spacing of 13mm.</p> / Thesis / Master of Applied Science (MASc)