Dissertations / Theses on the topic 'Metal hydroxides; High resolution'

The primary aim of the work presented in this thesis is to elucidate novel information regarding the uptake, storage, distributions, and functions of both copper and zinc in mammalian cells by predominantly using a combination of the high resolution imaging modalities, synchrotron radiation X-ray fluorescence microscopy (SXRF) and standard fluorescence imaging. Results from studies using cell permeable, metal ion selective fluorescent probes suggested the presence of labile pools of copper and zinc localized within the mitochondria and Golgi apparatus. Furthermore, SXRF imaging of a cell line defective in the copper transporter, Atox1, revealed intriguing differences in the Cu distribution of Atox1-/- cells compared to the corresponding wild-type cells. Finally, spatially well-resolved SXRF elemental maps of single, adherent mouse cells revealed remarkable changes in the distributions of both zinc and copper as the cells progressed through the cell cycle. Taken together, findings suggested major roles for copper and zinc within a native biological setting.

Several hydrides of Group 2 and 12 elements were generated in the gas phase using an emission source that combines an electrical discharge with a high temperature furnace, and their high-resolution infrared emission spectra were recorded with a Fourier transform spectrometer. Two classes of molecules were studied: a) diatomic metal hydrides BeH, MgH, CaH, SrH, ZnH and CdH; b) linear triatomic metal hydrides BeH₂, MgH₂, ZnH₂ and HgH₂.

Infrared emission spectra of BeH, MgH, CaH, SrH, ZnH and CdH free radicals contained several vibration-rotation bands in their ²SIGMA⁺ ground electronic state. The new data were combined with all the previous ground state data from diode laser infrared spectra and pure rotation spectra available in the literature. Spectroscopic constants, i. e. , vibrational band origins, rotational, centrifugal distortion, and spin-rotation interaction constants, were determined for each observed vibrational level by least-squares fitting of all the data. In addition, the data from all isotopologues were fitted simultaneously using the empirical Dunham-type energy level expression for ²SIGMA⁺ states, and correction parameters due to the breakdown of the Born-Oppenheimer approximation were determined. The equilibrium internuclear distances (r_e) of ⁹BeH, ²⁴MgH, ⁴⁰CaH, ⁸⁸SrH, ⁶⁴ZnH and ¹¹⁴CdH were determined to be 1. 342424(2), 1. 729721(1), 2. 002360(1), 2. 146057(1), 1. 593478(2) and 1. 760098(3) angstroms, respectively, and the corresponding r^e distances for ⁹BeD, ²⁴MgD, ⁴⁰CaD, ⁸⁸SrD, ⁶⁴ZnD and ¹¹⁴CdD are 1. 341731(2), 1. 729157(1), 2. 001462(1), 2. 145073(1), 1. 593001(2) and 1. 759695(2) angstroms, respectively.

Gaseous BeH², MgH², ZnH² and HgH² molecules were discovered and unambiguously identified by their high-resolution infrared emission spectra. The ν₃ antisymmetric stretching fundamental band and several hot bands in the ν₃ region were rotationally analyzed, and spectroscopic constants were obtained for almost all naturally-occurring isotopologues. The rotational constants of the 000 ground states were used to determine the r₀ internuclear distances. For BeH₂, ZnH₂, ZnD₂, HgH₂ and HgD₂ molecules, the rotational constants of the 000, 100, 01¹0 and 001 levels were used to determine the equilibrium rotational constants (B_e) and the associated equilibrium internuclear distances r_e. The r_e distances of ZnH₂ and ZnD₂ differed by about 0. 01%, and those of HgH₂ and HgD₂ differed by about 0. 005%. These discrepancies were larger than the statistical uncertainties by one order of magnitude, and were attributed to the breakdown of the Born-Oppenheimer approximation.

The first pure-rotational spectra of two transition-metal sulfides, copper sulfide (CuS) and manganese sulfide (MnS) have been determined. In addition, the millimeter/sub-millimeter spectra of SrS, SrNH₂ and SrND₂ have been determined for the first time. Electronic ground states have been confirmed with experimental evidence. Results indicate that the bonding trends of the transition-metals sulfides are slightly different than their isovalent analogs, the transition-metal oxides. Furthermore, the study of MnS has allowed for experimental testing of current high spin-state quantum theory, by analysing the spectra using third and fourth-order corrections to the effective Hamiltonian. Highly accurate spectroscopic constants and rotational transition frequencies have been determined for all species.

Small diatomic and triatomic 3d transition metal species are excellent model systems for understanding metal-ligand interactions important to larger complexes. Because of the unpaired 3d electrons, these radicals often occur in states with high angular momentum (electron spin, orbital, or nuclear spin). Three questions are particularly relevant to studying monosubstituted 3d metal compounds. What are the fundamental geometric, bonding, and electronic properties? How accurately does currentquantum mechanical theory describe the interactions in high spin states? Assuming these molecules may be present in the interstellar medium, what are the precise transition frequencies that can be used for radioastronomy?To answer these questions, pure rotational spectroscopy has been applied to eleven simple molecules containing 3d transition metals. The small radicals were synthesized in the gas phase and examined in situ. Both direct absorption, submillimeter spectroscopy and Fourier transform microwave spectroscopy were used to cover thefrequency range 8-660 GHz. New synthetic techniques, including oven-insulating methods, use of a longitudinal AC discharge, and emphasis on organometallic precursors, were developed to improve reaction yields.Spectra were recorded for four categories of 3d metal compounds: vanadium molecules, cobalt radicals, zinc species, and several monocyanides. Frequently, the data exhibited signs of perturbations either from low-lying excited electronic states, a common feature with 3d electrons, or from avoided crossings of hyperfine levels. The data were analyzed using effective Hamiltonians, and spectroscopic constants have been determined for rotational, fine structure, and hyperfine interactions. The measurements haveprovided transition frequencies as references for astronomical studies; these values are accurate to within 50 kHz for direct measurements and usually within 100 kHz for frequencies calculated from determined molecular constants.Rotational constants have been used to establish precise molecular geometries. Fine structure and hyperfine data provided insight into 3d metal bonding properties (molecular orbital composition and electron distribution) and structure of electronic state manifolds. In some cases, it was necessary to develop new terms for the Hamiltonian expressions to accurately describe the interactions observed in the spectra. These terms include deperturbation parameters and the first complete description of lambda-doubling for Phi states.

Millimeter-wave spectroscopy has been used in this thesis to accomplish two main goals: (1) to study bonding, structural, and electronic properties of small, metal-bearing molecules in their ground electronic states, in particular how individual metal atoms bond to small ligands, and (2) to provide rest frequencies for radio astronomical searches of metal containing species in the interstellar medium. The types of molecules studied in this thesis can be broadly classified into three groups: (1) alkali and alkaline-earth amides (MNH₂), (2) diatomic molecules in high electron spin or high orbital angular momentum electronic ground states (MX), and (3) transition metal cyanides (MCN). In this first category, the pure rotational spectra of LiNH₂ (X¹A₁), LiND₂ (X¹A₁), NaND₂ (X¹A₁), MgNH₂ (X²A₁), and MgND₂ (X²A₁), were recorded and analyzed. For each, the first experimental monomer r₀ structures were determined. These species were found to be planar and not invert, in contrast to ammonia. In addition, for the alkaline-earth amides, the M-N bond appears to become less ionic from Sr to Ca to Mg. The second class of molecules investigated, high-spin diatomcs, includes: NaC(X⁴Σ⁻), CrN(X⁴Σ⁻), CrO(X⁵Πᵣ), MnF(X⁷Σ⁺), FeN(X²Δᵢ), FeC(X³Δᵢ), and TiF(X⁴Φᵣ). These species represent examples of electronic states that have never or seldom been observed by high-resolution millimeter-wave spectroscopy, due to their high values of electron spin and orbital angular momenta. The analysis of their spectra has been used to test the adequacy of the effective Hamiltonians developed to model their rotational spectra; in particular the use of theoretically predicted higher order parameters. The final group studied includes the transition metal cyanides CoCN (X3Φᵢ ) and NiCN (X2Δᵢ). Unlike their alkali, alkaline-earth, and group 13 counterparts, these species were determined to be linear cyanides with the metal atom bonded to carbon, similar to both CuCN (X1Σ⁺) and ZnCN (X2Σ⁺). For both molecules, complications in the rotational spectra due to the Renner-Teller effect were observed and analyzed.

Three-dimensional porous single crystals (PSCs) are a recent development in the growing world of mesoporous material. The mesoporosity allows for the material to retain their nanoproperties whilst being bulk in size. The current work concentrates on chromium oxide and cobalt oxide PSCs formed in the templates SBA-15 and KIT-6. HRTEM is the main technique used in this investigation, looking at the morphology and single crystallinity of these materials. A growth mechanism for the PSC material is proposed based on HRTEM observations. XRD studies revealed that the confinement effect, caused by the mesopores, reduces the temperature for both cobalt and chromium oxide crystallisation, as well as a different intermediate route from the metal nitrates. The properties of chromium oxide PSC are also investigated magnetically and catalytically. Some metal oxides in different templates are also presented, despite no PSC forming. HRTEM work on other nanomaterials, based on collaboration, is also presented.

It was once thought that molecules in the interstellar medium (ISM) would be destroyed in the harsh surroundings and conditions of space, and therefore unobservable by radio techniques. However, it is now understood that the chemistry of the ISM is vast and complex. The question still remains as to just how complex is this chemistry. Much is clearly still not understood. This dissertation presents work on the study of metal compounds and cations in the circumstellar envelopes of oxygen- and carbon-rich asymptotic giant branch (AGB) and supergiant stars. Laboratory studies were also conducted on several transition metal compounds of interstellar interest, some with high spin and orbital angular momentum states. Work has been completed to confirm the detection of the debated metal cyanide KCN in the carbon-rich AGB star IRC+10216. KCN joins the list as the fifth interstellar metal cyanide/isocyanide detected in this source. In addition, preliminary results on the search for TiO are presented towards the oxygen-rich supergiant star, VY CMa. To further understand the evolutionary processes of carbon- and oxygen-rich stars, a survey of HCO⁺ was taken towards the carbon star IRC+10216, the oxygen-rich AGBs TX Cam, IK Tau, and W Hya and the oxygen-rich supergiant NML Cyg. While HCO⁺ was detected towards all of these sources, the results vary. The outflow of NML Cyg proves to be asymmetric and further study is necessary. The emission from W Hya is significantly narrower than the other sources. The abundances of HCO⁺ in circumstellar gas increases inversely with mass-loss rate and ion-molecule chemistry appears to influence the chemistry of evolved circumstellar envelopes. To understand species in space with more confidence, a laboratory search for several 3d transition metal species of astrochemical interest was conducted in the laboratory: HZnCl (X¹∑⁺), ZnO (X¹∑⁺ and a³Πᵢ), ZnCl (X²∑⁺), TiS (X³Δᵣ) and CrS (X⁵Πᵣ). All of the molecules have been observed for the first time with high resolution gas phase rotational spectroscopy and the work on ZnO was the first gas-phase study of this molecule. Synthesis of the species required exotic production methods, including use of a DC discharge to produce all zinc species. By studying the rotational spectra, rest frequencies were determined that will be beneficial for future astronomical searches.

Magister Scientiae - MSc (Chemistry)
Although cadmium and lead chalcogenide quantum dot have excellent optical and photoluminescent properties that are highly favorable for biological applications, there still exists increasing concerns due to the toxicity of these metals. We, therefore, report the synthesis of new aqueous soluble IrSe quantum dot at room temperature utilizing a bottom-up wet chemistry approach. NaHSe and H2IrCl6 were utilized as the Se and Ir source, respectively. High-resolution transmission electron microscopy reveals that the synthesized 3MPA-IrSe Qd are 3 nm in diameter. The characteristics and properties of the IrSe Qd are investigated utilizing, Selected Area electron diffraction, ATR- Fourier Transform Infra-Red Spectroscopy, Energy Dispersive X-ray spectroscopy, Photoluminescence, Cyclic Voltammetry and chronocoulometry. A 3 fold increase in the optical band gap of IrSe quantum dot in comparison to reported bulk IrSe is observed consistent with the effective mass approximation theory for semiconductor materials of particles sizes < 10 nm. The PL emission of the IrSe quantum dot is at 519 nm. Their electro-activity is studied on gold electrodes and exhibit reduction and oxidation at - 107 mV and +641 mV, with lowered reductive potentials. The synthesized quantum dot are suitable for low energy requiring electrochemical applications such as biological sensors and candidates for further investigation as photoluminescent biological labels.

Els efectes del canvi climàtic incideixen directament en les poblacions de microorganismes fotòtrofs dels tapissos microbians, produint alteracions en altres paràmetres ambientals com és l’increment de la temperatura, que pot provocar sequeres i fins i tot la desertització d’aquests ecosistemes, així com altres efectes en l’osmolaritat de les cèl·lules, degut a l’augment de la salinitat. Els microorganismes esmentats són molt abundants en els tapissos microbians, principalment els cianobacteris i les microalgues, que a més de ser els principals estabilitzadors d’aquests ecosistemes, al mateix temps es troben exposats a diferents condicions d’estrès. La majoria dels estudis que es realitzen per valorar l’impacte que tenen sobre els microorganismes condicions ambientals tan variables utilitzen cultius axènics que provenen de microorganismes aïllats de l’ambient natural o bé de col·leccions de cultius; res més lluny de la realitat, ja que en els ambients naturals els microorganismes fotòtrofs estableixen associacions estables amb microorganismes heteròtrofs i, a vegades, amb altres fotòtrofs. A més, hi ha pocs estudis que analitzin, en aquestes condicions i a nivell individual, els efectes dels paràmetres ambientals o de la pol·lució per metalls en aquestes associacions. La manca de metodologies que poden aplicar-se per esbrinar aquests efectes en un microorganisme en concret, quan està associat amb un altre de manera selectiva, in vivo, de manera ràpida i sense l’ús de cap tipus de tinció, és, per tant, un repte a la hora d’analitzar les possibilitats que tenen aquests microorganismes enfront a canvis tan dràstics. En aquest treball, s’ha intentat solucionar aquesta problemàtica mitjançant l’optimització de diferents tècniques que tenen com a base el microscopi làser confocal, considerant la principal característica dels cianobacteris i les microalgues, que és la d’emetre fluorescència natural. La clorofil·la a és el pigment majoritari d’aquests microorganismes i s’ha utilitzat amb anterioritat com a bioindicador, especialment en estudis realitzats en metalls per altres membre del grup. Així mateix, una problemàtica important és esbrinar el paper que juguen aquests microorganismes en la resistència davant canvis sobtats de les condicions naturals o antropogèniques. En aquest sentit, també s’ha accentuat l’interès en les anomenades cèl·lules dorments i en l’estudi de cèl·lules viables i no viables. Per aquest motiu, en aquest treball s’ha posat a punt una nova metodologia que utilitza el microscopi làser confocal i dos làsers específics i que ha permès determinar el percentatge d’aquestes cèl·lules en mostres exposades a diferents condicions d’estrès. Els microscopis electrònics de rastreig i transmissió, ambdós acoblats a un detector d’energia dispersiva de raigs X, juntament amb el microscopi de transmissió de raig X del sincrotró ALBA, s’han aplicat en mostres sotmeses a varis factors d’estrès per avaluar els canvis morfològics en cèl·lules senceres i en seccions ultrafines, així com en estudis de captació de metalls extra- i intracel·lularment. Els objectius del present treball s’han centrat en l’aplicació combinada de totes aquestes metodologies en dos consorcis de microorganismes: Scenedesmus sp. DE2009 i Geitlerinema sp. DE2011. L’efecte de la llum i la salinitat (com a paràmetres ambientals), així com l’impacte del plom, coure i crom (com a contaminants), s’ha estudiat àmpliament en cèl·lules individuals d’ambdós microorganismes. Finalment, aquesta tesi està estructurada en diferents capítols. El Capítol 3 correspon amb els articles publicats (un d’ells en revisió); així doncs, els resultats obtinguts de les investigacions realitzades s’exposen en les Seccions 3.1, 3.2 i 3.3 i es discuteixen globalment en el Capítol 4.
Los efectos del cambio climático inciden directamente en las poblaciones de microorganismos fototróficos de los tapices microbianos, produciendo alteraciones en otros parámetros ambientales como es el incremento de la temperatura, que puede provocar sequías y hasta la desertización de estos ecosistemas, así como otros efectos en la osmolaridad de las células, debido al aumento de la salinidad. Dichos microorganismos son muy abundantes en los tapices microbianos, principalmente las cianobacterias y las microalgas, que además de ser los principales estabilizadores de estos ecosistemas, a veces se encuentran expuestos a diferentes condiciones de estrés. La mayoría de los estudios, que se realizan para valorar los efectos que tienen sobre los microorganismos condiciones ambientales tan variables, utilizan cultivos axénicos que provienen de microorganismos aislados del ambiente natural o bien de colecciones de cultivos; nada más lejos de la realidad, ya que en los ambientes naturales los microorganismos fototróficos establecen asociaciones estables con microorganismos heterotróficos y, a veces, con otros fototróficos. Además, hay pocos estudios que analicen, en estas condiciones y a nivel individual, los efectos de los parámetros ambientales o de la contaminación por metales en estas asociaciones. La falta de metodologías que pueden aplicarse para averiguar estos efectos en un microorganismo en concreto, cuando está asociado con otro de manera selectiva, in vivo, de manera rápida y sin el uso de ningún tipo de tinción, es, por tanto, un reto a la hora de analizar las posibilidades que tienen estos microorganismos frente a cambios tan drásticos. En este trabajo, se ha intentado solucionar dicha problemática mediante la optimización de distintas técnicas que tienen como base el microscopio láser confocal, considerando la característica principal de las cianobacterias y las microalgas, que es la de emitir fluorescencia natural. La clorofila a es el pigmento mayoritario de estos microorganismos y se ha utilizado con anterioridad como bioindicador, especialmente en estudios realizados en metales por otros miembros del grupo. Asimismo, una problemática importante es valorar el papel que juegan estos microorganismos en la resistencia ante cambios repentinos de las condiciones naturales o antropogénicas. En este sentido, también se ha incrementado el interés por las denominadas células durmientes y en el estudio de células viables y no viables. Por este motivo, en este trabajo se ha puesto a punto una nueva metodología que utiliza el microscopio láser confocal y dos láseres específicos y que ha permitido determinar el porcentaje de estas células en muestras expuestas a diferentes condiciones de estrés. Los microscopios electrónicos de rastreo y transmisión, ambos acoplados a un detector de energía dispersiva de rayos X, junto con el microscopio de transmisión de rayos X del sincrotrón ALBA, se han aplicado en muestras expuestas a varios factores de estrés para evaluar los cambios morfológicos en células enteras y en secciones ultrafinas, así como para los estudios de captación de metales extra- e intracelularmente. Los objetivos de este trabajo se han centrado en la aplicación combinada de todas estas metodologías en dos consorcios de microorganismos: Scenedesmus sp. DE2009 y Geitlerinema sp. DE2011. El efecto de la luz y la salinidad (como parámetros ambientales), así como el impacto de metales como plomo, cobre y cromo (como contaminantes), se ha estudiado ampliamente en células individuales de ambos microorganismos. Finalmente, esta tesis está estructurada en distintos capítulos. El Capítulo 3 corresponde con los artículos publicados (uno de ellos en revisión); así pues, los resultados obtenidos de las investigaciones realizadas se exponen en las Secciones 3.1, 3.2 y 3.3 y se discuten globalmente en el Capítulo 4.
The effects of climate change directly affect the populations of phototrophic microorganisms in microbial mats, causing alterations in other environmental parameters such as the increase in temperature. This in turn causes drought and sometimes the desertification of these ecosystems, as well as affecting the osmolarity of cells due to the increase in salinity. The microorganisms referred to are highly abundant in microbial mats; principally, they are cyanobacteria and microalgae, which, apart from being the main stabilisers of these ecosystems, are exposed to distinct stress conditions at the same time. Most studies carried out to assess the impact on microorganisms of such variable environmental conditions use axenic cultures that come from microorganisms isolated from the natural environment or else from culture collections. Nothing could be further from reality, since—in natural environments—phototrophic microorganisms establish stable associations with heterotrophic bacteria and, at times, with other phototrophs. In addition, very few studies analyse (in these conditions and at individual level) the effects of environmental parameters or of metal pollution in these associations. The lack of methodologies that can be applied to ascertain these effects in a specific microorganism, when this is selectively associated with another, in vivo, swiftly and without using any type of staining, is therefore a challenge in analysing the possibilities of these microorganisms when facing such drastic changes. In the current work, an attempt has been made to solve this problem by means of the optimisation of distinct techniques, based on confocal laser microscopy and centring on the main characteristic of cyanobacteria and microalgae, which is the emission of natural fluorescence. Chlorophyll a is the majority pigment in these microorganisms and has previously been used as a bioindicator, in studies carried out with metals by other members of the group. Determining the role played by these microorganisms in the resistance to sudden changes in natural or anthropogenic conditions is a further, and important, issue. In addition, in this respect, the interest in dormant cells and in the study of viable and non-viable cells has increased. For this reason, a new methodology has been developed in this work; using a confocal laser microscope and two specific lasers, this has allowed us to ascertain the percentage of these cells in samples exposed to distinct stress conditions. The electronic scanning and transmission microscopes, both coupled to an X-ray dispersive energy detector, jointly with the X-ray transmission microscope from the ALBA synchrotron, have been used in samples prepared to evaluate morphological changes due to stress factors both in complete cells and in ultrafine sections, as well as in studies of extra- and intracellular metal extraction. The objectives of this work centre on the combined application of all these methodologies on two consortia of microorganisms: Scenedesmus sp. DE2009 and Geitlerinema sp. DE2011. The effect of light and salinity (as environmental parameters), in addition to the impact of lead, copper and chromium (as pollutants) was studied extensively in individual cells for both microorganisms. Finally, this thesis is organised into distinct chapters. The Chapter 3 correspond to the articles that have already been published (one of them currently under review); thus, the results obtained from the research carried out are therefore presented in Sections 3.1, 3.2 and 3.3 and are discussed globally in Chapter 4.

One of the most challenging goals in nanoparticle research is to develop successful protocols for the large-scale, simple and possibly low-cost preparation of morphologically pure nanoparticles with enhanced properties. The work presented in this thesis was focused on the synthesis, characterisation and testing of magnetic nanoparticles and their potential applications. There are a number of magnetic nano-materials prepared for specific applications such as metal oxide nanoparticles encapsulated with various porous materials including Fe₃O₄/Fe₂O₃ coated with soft bio-organic materials such as glycol chitosan and bovine serum albumin and hard materials such as silica (SiO₂) and zinc sulphide (ZnS). The preparation of these materials was achieved principally by bottom-up methods with different approaches including micro-emulsion, precipitation, electrostatic and thermolysis processes. The thesis also presents the uses of various analytical techniques for characterising different types of nano-materials including Attenuated Total Reflection Fourier Transformer Infrared Vibrational Spectroscopy (ATR-FTIR), Ultraviolet Visible- Near Infrared (UV-Vis-NIR) Spectroscopy, Zeta Potentiometric Surface Charge Analysis, Superconducting Quantum Interference Device (SQUID) and Vibration Sample Magnetometry (VSM) for magnetic analysis and powder X-Ray Diffraction (XRD) for crystallographic pattern analysis. There are many applications of magnetic nanoparticles, including nano-carriers for biological and catalytic reagents. The magnetic nanoparticles can facilitate separation in order to isolate the carriers from solution mixtures as compared to many inefficient and expensive classic methods, which include dialysis membrane, electrophoresis, ultracentrifugation, precipitation and column separation methods. There are six key chapters in this thesis: the first chapter introduces the up-to-date literature regarding magnetic nano-materials. The uses of magnetic nano-materials in drug binding and for protein separation are discussed in the second and third chapters. The fourth chapter presents the use of magnetic nanoparticle in conjunction with a photo-catalytic porous overlayer for the photo-catalytic reduction of organic molecules. The fifth chapter describes different analytical techniques used for the characterisation of nanoparticles and the underlying principles and the experimental details are also given. The sixth chapter summarises the results and provides an overview of the work in a wider context of future applications of magnetic nanoparticles.

Cette these etudie trois problemes specifiques de la microscopie electronique a haute resolution : le transfert du contraste des images, leur interpretation au moyen de simulations et l'application de cette technique a la determination des structures locales dans les materiaux cristallins, au niveau atomique. Obtention de resultats originaux en ce qui concerne la microstructure de materiaux de type lamelllaire : dans les composes de type re::(6) se::(8) cl::(2), avant et apres insertion d'hydrazine, dans les composes de type mps::(3) et dans taps::(6)se

Etude des mecanismes d'interaction joint de grain dislocations lors de la deformation du bicristal, mettant en evidence la dissociation des dislocations entrant dans le joint, leur perte d'identite et l'interaction entre eux des residus. Determination des structures des dislocations residuelles. Apparition de precipites lors du recuit du bicristal deforme

Etude de cinq joints de grains de flexion d'axe 001, de grande coincidence (sigma=5, 65, 13, 25 et 41) par microscopie electronique haute resolution et relaxation numerique. Presentation d'une analyse en termes d'unites structurales-dislocation

Etude des possibilites d'ecarts a la stoechiometrie sur le sous reseau anionique des perovskites amn::(1-x) fe::(x)o::(3-y) (a=ca, sr, ba) par diffraction x et neutron, microscopie electronique haute resolution, spectre moessbauer et mesures magnetiques. Caracterisation de plusieurs types d'ordre des lacunes oxygene en fonction du cation a et du taux de mn

Ces bronzes de titane de type hollandite sont des composes a vfalence mixte de formule generale a::(x)tio::(2), avec a=k, rb, cs et 0,125