<p style="text-align: justify;">Kroz istoriju, otkrivanje novih materijala i njihovog dizajna dovodilo je do tehnolo&scaron;kih revolucija. U pro&scaron;lom veku, novi materijali naprednih svojstava uveli su elektronske uređaje u svakodnevni život čoveka. Industrija mikročipova predstavlja ogroman deo svetskog trži&scaron;ta, i traži neprestan razvoj da bi pružila bolje proizvode potro&scaron;ačima. Početkom ovog veka, nova grupa materijala, pod nazivom multiferoici, privukla je pažnju naučno-istraživačkog dru&scaron;tva u svetu. Ovi materijali poseduju jedinstvenu karakteristiku da istovremeno ispoljavaju vi&scaron;e od jedne feroične osobine (feroelektričnost, feromagnetizam, feroelastičnost), a &scaron;to je jo&scaron; važnije, mogu da ostvare interakciju među njima. Naime, magnetizacija multiferoika se može postići primenom spolja&scaron;njeg električnog polja, a takođe se mogu i polarisati primenom spolja&scaron;njeg magnetnog polja. Ovo vrlo interesantno svojstvo otvara potencijlanu primenu u oblasti hibridne računarske memorije, senzora, aktuatora, i dr. Sredinom pro&scaron;log veka, jednofazni multiferoici su prvi privukli pažnju, ali poseldnjih godina, kompozitni multiferoici su pokazali bolje rezultate u pogledu funkcionalnih karakteristika. Trend minijaturizacije je takođe prisutan u ovoj oblasti, stoga su multiferoični tanki filmovi vrlo atraktivni u istraživačkih krugovima ne samo zbog niske potro&scaron;nje električne energije, malog utro&scaron;ka meterijala i malih dimenzija, već i zbog dobre magnetoelektrične interakcije.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Glavni cilj ove doktorske disertacije je bio određivanje optimalnog procesa sinteze/depozicije, i vr&scaron;enje strukturne i funkcionalne karakterizacije multiferoičnih vi&scaron;eslojnih tankih filmova, sačinjenih od naizmenično deponovanih feroelektričnih BaTiO₃ i fero/ferimagnetnih NiFe₂O₄ slojeva (uglavnom na silicijumskim supstratima sa slojem platine). Različite strukture slojeva dizajnirane su u cilju određivanja optimalne, koja bi dala najvi&scaron;e vrednosti magnetoelektričnog efekta.&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; U prvom koraku, sintetisani su stabilni solovi/rastvori prekursora, veličine čestica od nekoliko nanometara, reolo&scaron;kih karakteristika pogodnih za depoziciju tehnikama iz tečne faze. Vi&scaron;eslojni filmovi su dobijeni &quot;spin&quot; procesom nano&scaron;enja, pri čemu je termički tretman svakog sloja na 500 &deg;C bio neophodan radi potpunog otparavanja zaostalog rastvarača. Filmovi bez pukotina, ukupne debljine ispod 1 &mu;m, uniformne debljine sloja (60 nm sloj BaTiO₃ i 40 nm sloj NiFe₂O₄) i ravne povr&scaron;ine mogu biti dobijeni sinterovanjem u temperaturnom opsegu od 750 do 900 &deg;C. Strukturna karakterizacija je potvrdila sistem bez prisustva sekundarnih faza, sačinjen od perovskitnog BaTiO₃ i spinelnog NiFe₂O₄. Dielektrična merenja su bila u saglasnosti sa mikrostrukturnom analizom, i vrednostima dielektrične konstante tipične za nanostrukturni sistem, niske vrednosti dielektričnih gubitaka i male provodljivosti. Uticaj međuslojne polarizacije, koja nalikuje Debajeovoj relaksaciji, izražena kroz povećanje dielektrične konstante uspod 100 kHz, bio je jači u nižoj frekventnoj regiji na povi&scaron;enim temperaturama usled termičke aktivacije nosilaca naelektrisanja u feritnoj fazi. Samo čist BaTiO₃ film je pokazao slab feroelektrični histerezis nepotpune saturacije, malo vi&scaron;e polarizacije filma sinterovanog na 900 &deg;C usled ogrubljivanja strukture. Meuđuslojni efekti su takođe primećeni kod feroelektričnih merenja na sobnoj temperaturi, sa izraženijim prisustvom kada se primeni jače električno polje. Na osnovu dielektričnih i feroelektričnih merenja, zaključeno je da film sa debljim titanatnim i tanjim feritnim slojevima ima najverovatnije najbolji dizajn slojeva. Magnetne histerezisne petlje su snimljene na sobnoj temperaturi za čiste NiFe₂O₄ filmove i vi&scaron;eslojne filmove. Analizom vi&scaron;eslojnih filmova različitog dizajna slojeva, pretpostavljeno je da zatezanje nastalo mehaničkom interakcijom između titanatnih i feritnih slojeva jeste prisutno, i da raste sa povećanjem broja kontaktnih povr&scaron;ina, stoga film sa tanjim titanatnim i feritnim slojevima verovatno predstavlja najbolji izbor sa aspekta megnetnih osobina.</p> / <p>Through history, discovery of new materials and material design have led to technological revolutions. In the last century, new materials with advanced properties have introduced electronic devices in our everyday lives. Microchip industry represents one huge part of world market, and needs constant development to provide better products to consumers. In the beginning of this century, a novel group of materials, called multiferroics, have attracted close attention of research society around the world. These materials have a unique property to express more than one ferroic property simultaneously (feroelectricity, ferromagneticity, ferroelasticity), and more important, to achieve coupling between them. Namely, magnetization of multieferroic may be changed with application of external electric field, and they can be polarized with application of the external magnetic field. This is a very interesting property that opens the potential applications in fields of hybrid computer memory, sensors, actuators, etc. In the middle of last century, single phase multiferroics were the first to trigger interest in this special property, but in recent years, composite multiferroics have shown more promising results in terms of functional properties. The trend of miniaturization is also present in this field, so multiferroic thin films are very attractive for research not only because of low power and material consumption or small size, but also because of strong magnetoelectric coupling.<br />The main goal of this thesis was to determine optimal synthesis/deposition process, and perform structural and functional characterization of multiferroic multilayer thin films, composed of ferroelectric BaTiO3 and ferro/ferrimagnetic NiFe2O4 layers in alternating order (mostly on platinum coated silicon substrates). Different layer structures were designed in order to find optimal one which could show the strongest magnetoelectric effect.<br />In the first step, stable precursor sols/solutions were synthesized, with particle size of a few nanometes, and rheological properties suitable for solution deposition. The multilayered thin films were obtained by spin coating and thermal treatment of each layer on 500 &deg;C was necessary in order to completely evaporate traces of residual solvents. Crack free films with overall thickness below 1 &mu;m, uniform single layer thickness (60 nm of BaTiO3 layer and 40 nm of NiFe2O4) and flat surface can be obtained by sintering in temperature range from 750 to 900 &deg;C. Structural characterization confirmed that secondary phase free system with microstructure on nanometer scale was obtained, composed of perovskite BaTiO3 and spinel NiFe2O4. Dielectric measurements were in agreement with microstructural characterization, showing the values of dielectric constant typical for nanostructured system, low values of dielectric losses and low conductivity. The influence of interfacial polarization, resembling Debye behavior, expressed as a rise of dielectric constant below 100 kHz, was stronger in lower frequency range on higher temperatures due to thermal activation of mobile charge carriers in ferrite phase. Only the pure BaTiO3 films showed weak unsaturated ferroelectric hysteresis loops, with slightly higher polarization of films sintered on 900 &deg;C due to coarsening of the structure. The interface effects were also detected in ferroelectric measurements on room temperatures, showing increased presence when higher field is applied. Regarding dielectric and ferroelectric characterization, it was concluded that the multilayered films with thick titanate and thin ferrite layers may probably have the most promising layer design. Magnetic hysteresis loops were recorded on room temperatures for the pure NiFe2O4 and multilayers films. By analysis of different layer design of multilayers, it was assumed that mechanical straining between the ferrite and titanate layers may be present, and increases with the number of contact surfaces, thus the films with thinner titanate and ferrite layers may probably have the best layer design from aspect of magnetic properties.</p>

<p>U ovom radu sintetisani su kompozitni nanoprahovi i nanoprahovi tipa jezgro&ndash; omotač sa dielektričnom i magnetnom fazom, kao pogodan polazni materijal za procesiranje kompozitne keramike za primenu u mikroelektronici. Osnovni cilj ove doktorske disertacije je bio utvrđivanje veza između uslova sinteze, morfologije čestica, uslova procesiranja i mikrostrukture kompozitne keramike. Nanoprahovi su sintetisani hemijskim metodama sinteze u tečnoj fazi (sol-gel i koprecipitacija) i gasnoj fazi (CVS), pri čemu je vr&scaron;ena optimizacija procesnih uslova u cilju sinteze čestica željene strukture i hemijskog sastava. Istraživanja su vr&scaron;ena na nekoliko modelnih sistema sa feritima kao magnetnom fazom i titanatima ili silikom kao dielektričnom fazom: NiFe2O4SiO2, Fe3O4SiO2, SrTiO3NiFe2O4, BaTiO3NiFe2O4 i BaTiO3Fe3O4. Hemijska sinteza u tečnoj fazi se pokazala pogodnom zato &scaron;to pruža mogućnost kontrolisanja morfologije kompozitnih čestica ne samo pode&scaron;avanjem procesnih parametara sinteze već i funkcionalizacijom faza kojom se uzrokuje njihovo elektrostatičko privlačenje i formiranje strukture jezgro&ndash;omotač. Ipak, zbog velikog stepena aglomeracije prisutnog tokom sinteze u tečnoj fazi, dobijanje omotača uniformne debljine i izbegavanje homogene nukleacije faza se pokazalo te&scaron;ko. Hemijskom sintezom u gasnoj fazi (CVS) je po prvi put sintetisan kompozitni nanoprah na bazi kompleksnih oksida titanata i ferita.<br />Utvrđeno je da i pored velikog potencijala CVS metode u smislu sinteze ultrafinih prahova na bazi titanata i ferita u jednom koraku, ova metoda nudi relativno slabu kontrolu morfologije kompozitnih čestica pri visokim procesnim temperaturama koje su neophodne za kristalizaciju dve faze. Sintetisani nanoprahovi na bazi titanata i ferita (SrTiO3NiFe2O4 i BaTiO3NiFe2O4) procesirani su u gustu kompozitnu keramiku visokotemperaturnim sinterovanjem, u cilju ispitivanja veze morfologije čestica i mikrostrukture kompozita, optimizacije režima sinterovanja i funkcionalne karakterizacije dobijene keramike sa različitim masenim odnosom faza. Prahovi su sinterovani putem konvencionalnog sinterovanja u atmosferi vazduha, spark plazma sinterovanja (SPS) ili kombinacijom ove dve metode. Utvrđeno je da prahovi strukture jezgro&ndash;omotač densifikuju u značajno gu&scaron;ću i homogeniju keramiku u odnosu na kompozitne prahove istog sastava na istim procesnim temperaturama. Pored toga, pH vrednost sinteze čestica i atmosfera visokotemperaturnog sinterovanja su se pokazali veoma značajnim u smislu održavanja željenog faznog sastava dobijenih kompozita. U pogledu režima sinterovanja dobijenih prahova, kombinacija niskotemperaturnog konvencionalnog i SPS sinterovanja (1000 &deg;C) je dala najbolje rezultate u smislu postizanja zadovoljavajuće gustine kompozita (&gt;95% teorijske gustine), održavanja željenog faznog sastava i homogene distribucije faza. Funkcionalna karakterizacija sinterovane keramike sa različitim masenim odnosom faza (BaTiO3 : NiFe2O4 = 1,2,8) potvrdila je očekivano dielektrično, feroelektrično i ferimagnetno pona&scaron;anje dobijenih kompozita.</p> / <p>Composite and core&ndash;shell nanopowders with dielectric and magnetic phase have been synthesized in this work, as a suitable starting material for processing of composite ceramics for microelectronic application. The main goal of this doctoral dissertation was the determination of the link between synthesis conditions, particle morphology, processing conditions and microstructure of composite ceramics. Nanopowders have been synthesized by chemical synthesis methods in wet phase (sol&ndash;gel and coprecipitation) and gas phase (CVS), whereas the optimization of processing parameters was conducted with the goal to synthesize particles of desired structure and chemical composition. Studies were conducted on the few model systems with ferrites as a magnetic and titanates as a dielectric phase: NiFe2O4SiO2, Fe3O4SiO2, SrTiO3NiFe2O4, BaTiO3NiFe2O4 and BaTiO3Fe3O4. Chemical wet synthesis has proven suitable because it offers composite particle morphology control not only by adjustment of synthesis parameters but also by phase functionalization causing their mutual electrostatic attraction and thus core&ndash;shell structure formation. However, due to the high degree of agglomeration present during the wet phase synthesis, formation of the shell with uniform thickness and avoidance of homogeneous nucleation has proven difficult. For the first time, composite ferrite and titanate-based nanopowder has been synthesized by means of Chemical Vapor Synthesis (CVS). It has been found that beside high potential of CVS method for one-step synthesis of ultrafine titanate and ferrite-based nanopowders, this method offers relatively low control of composite particle morphology at high processing temperatures which are necessary for crystallization of both phases. Synthesized titanate and ferrite-based nanopowders (SrTiO3NiFe2O4 and BaTiO3NiFe2O4) were processed into dense ceramics by high-temperature sintering, in order to find the link between particle morphology and composite microstructure, optimize the sintering regime and conduct the functional characterization of obtained ceramics with different phase mass ratio.<br />The powders were sintered by conventional sintering in air, spark plasma sintering<br />(SPS) or combination of these two methods. It was found that core&ndash;shell powders densify in ceramics with considerably higher density and homogeneity at the same processing temperature, than the composite powders with the same composition. Moreover, synthesis pH value and sintering temperature was found to be very important in terms of phase composition preservation of obtained composites. Regarding the sintering regime of obtained powders, combination of low-temperature conventional and SPS sintering (1000 &deg;C) has given the best results in terms of achieving adequate composite density (&gt;95% theoretical density), phase preservation and homogeneous phase distribution. Functional characterization of sintered ceramics with different phase mass ratio (BaTiO3 : NiFe2O4 = 1,2,8) confirmed the expected dielectric, ferroelectric and ferromagnetic behaviour of obtained composites.</p>

L'antagonisme entre les besoins croissants d'énergie au niveau mondial et l'obligation de ralentir le réchauffement climatique fait partie des défis auquel l'humanité fait face. Dans le but d'assurer un confort thermique suffisant, les domaines de l'habitat, de l'automobile ou encore des bâtiments agricoles consomment de grandes quantités d'énergie. Pour réduire ces besoins, une des solutions proposées vise à améliorer l'isolation thermique de ces bâtiments grâce à l'utilisation de matériaux innovants. Un des objectifs majeurs est d'améliorer l'isolation des fenêtres qui représentent une partie importante des pertes énergétiques. Les recherches décrites dans cette thèse ont permis de développer des matériaux transparents aux rayonnements solaires visibles tout en étant des boucliers efficaces contre les rayonnements ultra-violets et proche-infrarouges. De tels matériaux sont le fruit de la combinaison entre des motifs à clusters de métaux de transition présentant des propriétés d'absorption recherchées et une matrice hôte permettant la mise en forme de ces matériaux (processabilité). La synthèse, ainsi que la méthodologie de modulation des propriétés d'absorption et d'intégration des clusters dans différentes matrices de type sol-gel ou polymères sont présentées. Un intérêt tout particulier est porté sur les relations qui s'établissent entre la structure des motifs à clusters et leurs propriétés d'absorption grâce aux comparaisons faites entre des études expérimentales et des études de chimie quantique utilisant la théorie de la fonctionnelle de la densité (DFT). In fine, l'augmentation du niveau de compréhension des relations structures-propriétés d'absorption des motifs à clusters étudiés permettra d'envisager l'étude de nouvelles compositions pour des matériaux encore plus efficaces à l'avenir pour le contrôle solaire. / The antagonism between growing global energy needs and the obligation to slow the global warming is one of the challenges humanity faces. In order to ensure sufficient thermal comfort, the housing, automotive or agricultural buildings sectors are major energy consumers. To reduce these needs, one of the proposed solutions aims to improve the thermal insulation of these buildings through the use of innovative materials. One of the major objectives is to improve the insulation of the windows which represent a significant part of the energy losses. The research described in this thesis has made it possible to develop transparent materials for visible solar radiation while being effective shields against ultraviolet and near-infrared radiation. Such materials are the result of the combination between transition metal cluster patterns having desired absorption properties and a host matrix for shaping these materials (processability). The syntheses as well as the methodology for modulating the absorption and integration properties of clusters in different sol-gel or polymer matrices are presented. Of particular interest is the relationship between the structure of cluster pattern and their absorption properties through comparisons between experimental studies and quantum chemistry studies using density functional theory (DFT). In fine, the increase in the level of understanding of the structure-absorption properties of the clusters studied will make it possible to consider the study of new compositions for even more efficient materials in the future for solar control.

This doctoral thesis is focused on the study of reactions in the CaO–SiO2–H2O complex system, primarily to the synthesis of crystalline tobermorite. Hydrothermal conditions are necessary for the formation of crystalline tobermorite, whereas the course of the reaction is influenced by several factors. The main studied factor was the choice of the silica sources differing in means of solubility, crystallinity, particle size distribution, specific surface area, and purity. The water-to-solid ratio turned to be also an important factor as the length of the hydrothermal reaction. The influence of the mechanochemical pretreatment of starting materials to the final phase composition of samples was studied as well. The obtained results show that the crystallinity of the silica source is the main factor influencing the reaction rate and the purity of the synthesized tobermorite. While using the crystalline silica source the shorter silicate chains are formed and the formation of tobermorite structure is easier. Using the amorphous silica sources and the mechanochemical pretreatement of starting materials prolong the hydrothermal reaction. The prepared samples are always the mixture of crystalline or semicrystalline calcium hydrosilicates instead of the phase pure tobermorite.

Diploma thesis deals with the research of oxide interphase of ceramic composite in dependence on the amount of precursor used in sol – gel method for deposition of titanium dioxide thin layer on corundum.

Les progrès fulgurants de l’informatique poussent au développement de dispositifs plus petits et plus puissants, impliquant la conception de matériaux continuellement plus complexes à l’échelle nanoscopique. Notre objectif est de développer, par une approche purement bottom-up, des nanoparticules magnétiques présentant de fortes anisotropies magnétiques (oxydes ou alliages) et localisées dans des nanoperforations bien organisées d'un film mince d’oxyde non magnétique. Notre approche originale pour synthétiser ces nanoparticules magnétiques comprend trois étapes: i) l’élaboration d’une matrice solide nanostructurée par chimie sol-gel en présence d’agents structurants, ii) la formation d’analogues du bleu de Prusse (ABP) dans la nanostructuration de ces matrices et iii) leur traitement thermique sous atmosphère contrôlée. Deux types de matrices solides nanostructurées ont été étudiées : les films minces de TiO2 nanoperforés, permettant d’organiser les particules sur une surface, et les monolithes de silice mésoporeux, permettant l’étude de la transformation des particules d’ABP en oxyde et alliage sur des quantités de matière plus importante que celle contenue dans les films nanoperforés. Les ABPs ont été choisis comme précurseurs pour la formation de ces particules magnétiques en raison de leur composition chimique et de leur structure particulièrement bien définies. En modulant la chimie très versatile des ABPs combinée à une parfaite maîtrise de leur stœchiométrie à l'échelle atomique, il devrait être possible de réguler finement la composition chimique, la structure et donc les propriétés magnétiques des alliages et des oxydes.Une méthode originale, mise au point au laboratoire, permet de confiner des particules d’ABPs à l’intérieur de monolithes de silice mésoporeux pour former des nanocomposites ABP/SiO2. Le traitement thermique de ces nanocomposites sous atmosphère contrôlée a été étudié de façon à obtenir des nanocomposites Oxyde/SiO2 et Métal/SiO2 présentant une mésoporosité parfaitement préservée ainsi que des nanoparticules bien confinées dans la porosité.La formation d’ABP dans les nanoperforations d’un film mince de TiO2 est réalisée grâce à l'immersion successive de ce film dans des solutions de précurseurs de l’ABP. Une étude systématique de chaque étape de la synthèse a permis d’aboutir à la formation de particules d’ABP à l’intérieur de chaque nanoperforation du film mince. Enfin, le traitement thermique sous atmosphère contrôlée a conduit à la transformation des particules d’ABPs en oxydes mixtes ou en alliages dans ces nanoperforations. / Remarkable progress in information technology has led to the development of smaller and more powerful systems. This effort requires the design of new materials which are more complex at the atomic scale. Our goal is to develop magnetic nanoparticles confined into the well-organized nanocraters of non-magnetic thin films that should present a strong magnetic anisotropy (as oxides or alloys). In order to synthesize these magnetic nanoparticles, our original bottom-up approach involves three steps : i) elaboration of a solid nanostructured matrix via sol-gel chemistry in the presence of structuring agents, ii) formation of Prussian Blue Analogues (PBA) in the pores of this matrix and iii) thermal treatment under a controlled atmosphere. Two types of nanostructured matrices have been investigated : nanoperforated TiO2 thin films, in order to organize particles on a surface, and mesoporous silica monoliths, which allow to study the transformation of a larger amount of PBA nanoparticles into oxide or alloy than in the case of thin films. PBAs were chosen as precursors for the formation of magnetic particles because of their well-defined chemical composition and structure. PBA chemistry is versatile and the stoichiometry and structure of the resulting coordination polymer can be perfectly controlled at the atomic scale. Controlling PBA chemistry should thus enable us to finely tune the chemical composition and structure of the corresponding alloys and oxides and hence their magnetic properties.An original method, developed in our laboratory, results in well-confined PBA particles within the organized porosity of a mesoporous silica monoliths to form PBA/SiO2 nanocomposites. The thermal treatment of these nanocomposites under different controlled atmospheres was then investigated in order to get Oxide/SiO2 and Metal/SiO2 nanocomposites with a perfectly preserved mesoporosity and well-confined nanoparticles with controlled chemical composition, size and shape.The PBA formation inside the nanocraters of a TiO2 thin film is performed by successive immersions of the film in the PBA precursor solutions. A systematic study of each step of the synthesis leads to the formation of PBA particles within each nanoperforation in the thin film. Finally, the thermal treatment under different controlled atmospheres enabled the transformation of PBA particles into oxides or alloys inside the nanoperforations.

<p>U ovom radu su sintetisani prahovi na bazi lantan-galata, citratnom sol-gel<br />metodom i hemijskom sintezom u parnoj fazi (CVS), a njihovim presovanjem<br />i sinterovanjem su dobijeni keramički uzorci kontrolisane mikrostrukture. Cilj<br />disertacije je bio dobijanje guste keramike koja bi mogla da se primeni kao<br />jonski provodni elektrolit u gorivnim ćelijama sa čvrstim elektrolitom (SOFC),<br />a koje bi radile na srednjim temperaturama od 500&ndash;700 &deg;C (IT-SOFC). Po prvi<br />put su sintetisani nanoprahovi lantan-galata u gasnoj fazi i utvrđeno je da ovako<br />dobijeni polazni prahovi, zbog svojih superiornih karakteristika omogućavaju<br />snižavanje temperature sinterovanja za 150 &deg;C, &scaron;to je veoma povoljno kako sa<br />stanovi&scaron;ta dizajniranja mikrostrukture, tako i zbog u&scaron;tede energije u procesu<br />proizvodnje gorivnih ćelija. Ipak, zbog nedovoljne kontrole hemijskog sastava<br />i stehiometrije sintetisanih prahova, &scaron;to je i najveći nedostatak CVS metode<br />dobijanja perovskitnog LaGaO₃, nije bilo moguće dobiti keramiku koja bi ispunjavala zahteve za primenu u SOFC. S druge strane, citratna sol-gel metoda<br />pruža veliku kontrolu pomenutih parametara zbog čega je bila moguća sinteza<br />čitavog niza čvrstih rastvora lantan-galata. Ovom metodom su tako sintetisani<br />čist lantan-galat (LG) i dopirani prahovi kod kojih je deo lantana supstituisan<br />stroncijumom, a deo galijuma magnezijumom: La_0,85Sr_0,15Ga_0,85Mg_0,15O_3-<br />La_1-xSr_xGa_0,8Mg_0,2O_3-, gde je x = 0,10, 0,15 ili 0,20 (LSGM). Svi ovako sintetisani</p><p>prahovi su zahtevali naknadnu kalcinaciju na 900 &deg;C, ali su potrebne<br />gustine (&gt;95% teorijske gustine) postignute sinterovanjem na temperaturi<br />od 1450 &deg;C već nakon 2 h, &scaron;to je izuzetno kratko imajući u vidu literaturne<br />podatke. Takođe, sinterovani uzorci su po faznom sastavu bili čista LSGM<br />keramika, a impedansna merenja su pokazala da je najveću provodljivost imao<br />uzorak La_0,85Sr_0,15Ga_0,8Mg_0,2O_3-. Ovaj sastav je dalje kori&scaron;ćen u cilju provere</p><p>mogućnosti za dodatno povećanje provodljivosti te su pripremljeni i uzorci kod kojih je izvr&scaron;ena parcijalna supstitucija magnezijuma sa niklom ili kobaltom:<br />La_0,85Sr_0,15Ga_0,8Mg_0,2-yMyO_3-, gde je M = Ni ili Co, a y = 0,03 ili 0,05 (LSGMN i</p><p>LSGMC). Pokazano je da dodatak male količine prelaznih metala značajno utiče<br />na mehanizam provođenja, ali da je na vi&scaron;im temperaturama jonska provodljivost<br />i dalje dominantna. Konstatovano je da se dodavanjem male količine Ni ili Co u<br />LSGM mogu dobiti materijali koji bi služili kao elektroliti u IT-SOFC, pri čemu je<br />potencijal nikla kao dopanta ne&scaron;to veći nego kobalta.</p> / <p>Powders based on lanthanum-gallate have been synthesised in this work by using citrate sol-gel method in the liquid phase and by chemical vapour synthesis (CVS). As-synthesised powders were calcined, pressed and finally sintered in order to produce ceramic samples with controlled microstructure. The main goal of this dissertation has been obtaining of dense ceramics for application in ion conducting electrolyte for solid oxide fuel cells working at 500&ndash;700 &deg;C (IT-SOFC). Lanthanum-gallate nanopowders have been synthesised in the gas phase for the first time and it has been determined that these starting powders posses superior properties which could lower down the sintering temperature for about 150 &deg;C. This is very significant considering microstructure design, but also high energy consumption during the manufacturing process of fuel cells. However, it has not been possible to obtain ceramics with exact properties needed for SOFC application using CVS due to the lack of control of chemical composition and stoichiometry of the as-synthesised powders, which are the main drawbacks of this method. On the other hand, citrate sol-gel method offered a possibility to precisely control aforementioned parameters which enabled synthesis of a whole range of lanthanum-gallate sollid solutions. So, pure perovskite lanthanum-gallate (LG) has been synthesised by using this liquid phase method, but also doped powders where part of lanthanum and gallium was supstituted with strontium and magnesium, respectively: La_0,85Sr_0,15Ga_0,85Mg_0,15O_3-and La_1-xSr_xGa_0,8Mg_0,2O_3-, where x = 0.10, 0.15 or 0.20 (LSGM). Calcination at 900 &deg;C was necessary step during the processing of these sol-gel powders but the sintering time at 1450 &deg;C was only 2 h which is quite short in comparison with available literature data. Additionaly, the sintered samples were phase pure LSGM ceramics and impedance measurement showed that the highest conductivity had sample La_0,85Sr_0,15Ga_0,8Mg_0,2O_3-. Accordingly, this composition has been used to check the possibility of further improvement of conductivity. A set of new samples has been prepared where one part of magnesium has been substituted with nickel or cobalt: La_0,85Sr_0,15Ga_0,8Mg_0,2-yMyO_3-, where M = Ni or Co and y = 0.03 or 0.05 (LSGMN i LSGMC). It has been shown that addition of small amount of transition metals significantly influences conduction mechanism, but at higher temperatures the ionic conductivity is still dominant. It has been found that electrolyte materials for IT-SOFCs could be obtained by incorporation of small quantities of Ni or Co into LSGM and that nickel is more promissing for this purpose than cobalt.</p>

La photocatalyse laisse entrevoir un large champ d’applications dans de nombreux domaines parmi lesquels figurent principalement ceux du traitement et de la purification de l’eau et de l’air. Ceci constitue une des raisons pour lesquelles les études fondamentales des processus de dégradation des molécules organiques à la surface des photocatalyseurs concernent le plus souvent les phases liquides et gazeuses. Les développements plus récents des applications de la photocatalyse dans le domaine des surfaces autonettoyantes ont soulevé des problématiques fondamentales concernant les mécanismes de dégradation photocatalytique de composés solides tels que les suies et les acides gras. Ces problématiques restent encore peu abordées dans la littérature malgré les enjeux majeurs en terme environnemental et méritent donc des travaux de recherche plus approfondis. Cette thèse porte sur l’étude des modes de dégradation photocatalytique de dépôts solides d’acide stéarique (AS) sur des couches minces de dioxyde de titane. Dans ce travail, des approches expérimentales originales basées sur la microscopie optique sont mises en œuvre pour suivre la dégradation photocatalytique de ces dépôts d’AS à l’échelle microscopique sous exposition à la lumière ultraviolette. Les dépôts d’AS se présentent sous forme d’îlots microscopiques présentant une distribution de taille et de forme. Sur la base d’un nouveau modèle cinétique que nous proposons, le lien existant entre la vitesse de dégradation photocatalytique du dépôt et la distribution de taille initiale de la population d’îlots est mis en évidence. Le modèle cinétique développé permet de rationaliser nos résultats et de concilier d’autres résultats, jusqu’alors contradictoires, de la littérature. Ce travail propose en outre une étude originale sur la dégradation photocatalytique de microcristaux d’AS déposés sur des couches minces de TiO2 microstructurées qui a permis d’appréhender le rôle des radicaux libres dans le processus de dégradation photocatalytique. La démarche expérimentale est basée sur le lien étroit existant entre l’orientation des molécules, inhérente à la structure propre des microcristaux, et les directions des plans cristallographiques {hkl}. Ainsi, nous mettons en évidence une dépendance en {hkl} des vitesses de dégradation des microcristaux qui est justifiée à l’échelle moléculaire par l’affinité des radicaux pour les terminaisons chimiques exposées selon ces plans cristallographiques / Photocatalysis is widely used in a variety of applications in water and air purification. For those reasons, fundamentals research on the photocatalytical degradation processes of organic compounds on photocatalysts surfaces concern in most cases liquid and gaseous phases. The more recent development of self-cleaning surfaces has raised several issues concerning the mechanisms of photocatalytic degradation of solid deposits such as soot or fatty acids. These issues remain little addressed in the literature and therefore deserve further attention. This thesis work deals with the study of the photocatalytical degradation modes of solid deposits of stearic acid (SA) on the surface of titanium dioxide thin films. In this work, an original experimental approach based on the use of optical microscopy is implemented to monitor, on a microscopic scale, the SA deposits as a function of UV light exposure. Viewed under microscope, the SA deposits appear as microscopic islands presenting size and form distribution. On the basis of a new kinetic model we propose, the existing relationships between the degradation rate of the deposit and the initial size distribution of the islands population is demonstrated. The proposed kinetic model rationalizes our experimental results as well as several others from the literature. Additionally, an original study on the degradation of SA microcrystals, grown on microstructured TiO2 thin films, provides insight into the role of the photogenerated oxygenated radicals in the photocatalytical mechanisms. Furthermore, the anisotropy of the microcrystals structure is put in relation with that of the SA molecules orientations within the microcrystal. This explains the observed {hkl}-dependence of the degradation rate of the microcrystals

The Ni-base superalloy, IN-718, has been coated with alumina sols. Coated surfaces, carrying alumina layers having thicknesses between 0.6 μm and 3.6 μm show a significantly reduced oxidation rate when compared with uncoated reference surfaces, even if heating temperature is increased up to 900 °C and heating time is extended to 800 h. Alumina layers were prepared via sol-gel processing using a modified Yoldas procedure to obtain alumina sols. No change in rheological sol behavior was observed for more than 1 year of aging under static conditions at room temperature. Depending on pH value, modified Yoldas sols contain a manifold of Al species, among them Al13 polycations. Thermal evolution of sol derived alumina powders depends on Al speciation of parent sols. Depending on sol composition, both gamma-Al2O3 and eta-Al2O3 occur as intermediate transition aluminas. Phase composition and gas phase velocity influence oxygen permeability of thin layers prepared with modified Yoldas sols.

Les nanoparticules d’or (AuNPs) intriguent tout particulièrement ces dernières années de par leurs propriétés fascinantes. Elles sont variables selon la forme et la taille des nanoparticules ce qui en fait des objets ouvrant des perspectives dans plusieurs domaines. L’or est d’autant plus intéressant qu’il a une grande flexibilité de ces bandes de résonance plasmon de surface, allant du visible au proche infrarouge (IR). Au cours de cette thèse, nous avons donc travaillé sur la synthèse d’AuNPs de tailles et de formes différentes pour pouvoir travailler à de nombreuses longueurs d’onde du visible à l’IR. Cette multitude de AuNPs nous a permis d’étudier l’effet de ces différentes résonances plasmons sur des chromophores afin d’essayer de comprendre les mécanismes de ces interactions. Le but final de ces travaux, outre l’amélioration de la compréhension de ces interactions, est la réalisation de matériaux monolithiques pour l’optique par une approche sol-gel permettant l’incorporation de molécules optiquement actives et de ces systèmes plasmoniques, qui donnent des propriétés intéressantes aux matériaux obtenus. Nous nous sommes intéressés plus précisément aux propriétés d’absorption non-linéaire, dans le but de réaliser des matériaux limiteurs optiques pour protéger des systèmes optiques contre des rayonnements intenses, comme les lasers. Ces systèmes ont commencé à être mis au point dans les thèses précédentes faites au laboratoire mais la compréhension amenée par ces travaux auront permis d’approfondir les interactions particules-chromophores et le rôle de la longueur d’onde de la résonance plasmon afin d’optimiser l’efficacité en limitation optique. / Gold nanoparticles (AuNPs) particularly intrigued over the last decades because of their fascinating properties. They vary according to the size and shape of nanoparticles making objects opening opportunities in many areas. Gold is especially interesting since it has a great flexibility of these resonance surface plasmon bands ranging from the visible to near infrared (IR).In this thesis, we worked on the synthesis of AuNPs of different sizes and shapes in order to be able to work in many wavelengths from visible to IR. This multitude of AuNPs enabled us to study the effect of these different plasmon resonances of chromophores in an effort to understand the mechanisms of these interactions. The ultimate goal of this work, in addition to improving the understanding of these interactions, is the realization of monolithic materials for optics by a sol-gel approach allowing the incorporation of optically active molecules and these plasmonic systems, which give interesting properties to the obtained materials. We focused specifically on nonlinear absorption properties, in order to produce optical limiting materials to protect optical systems against intense radiation, such as lasers.These systems began to be developed in previous PhD thesis made in our laboratory but the understanding brought by this work have helped deepen the particles-chromophore interactions and the role of the wavelength of the plasmon resonance in order to optimize efficiency in optical limiting.