As our understanding of ceramic processing methods for the purpose of fabricating polycrystalline optical materials has increased over the past few decades, the race is on to bring ceramic technology to markets where single crystalline materials have traditionally been used. One such market is scintillators. This Master’s thesis focuses specifically on a class of materials attractive for use as gamma-ray scintillators. These barium based halides can potentially be utilized in applications ranging from ionizing radiation detection in the field to high-energy physics experimentation. Barium bromide iodide and barium chloride single crystals have already showed high light yield, fast scintillation decay, and high energy resolution, all desirable properties for a scintillator. This work attempts to show the likelihood of moving towards polycrystalline scintillators to take advantage of the lower processing temperature, higher manufacturing output, and overall reduced cost. The experiments begin with identifying appropriate sintering conditions for hot pressed ceramics of BaBrI and BaCl2. Possible sources of optical loss in the first phase of hot pressed samples are investigated using a wide range of characterization tools. Preliminary luminescence and scintillation measurements are reported for a translucent sample of BaBrI. Recommendations are made to move toward highly transparent ceramics with scintillation properties approaching those measured in single crystal samples

Les conditions nécessaires pour obtenir des céramiques transparentes (absence de porosité, absence de seconde phase) requièrent une totale maitrise de chacune des étapes (synthèse, mise en forme, frittage) intervenant dans le processus, ce qui rend encore difficile l'industrialisation d'un procédé d'élaboration reproductible. Dans ce contexte, ce travail de thèse s’est focalisé à développer et évaluer la capacité du procédé de frittage micro-ondes à améliorer la robustesse du processus d'élaboration de spinelle transparent. La mise en place d'un dispositif de dilatométrie optique et une nouvelle technique de calibration originale, basée sur la fusion d'oxyde, ont permis de caractériser le frittage micro-ondes du spinelle pur avec une plus grande confiance. Même si aucun effet lié au procédé micro-onde n’a pu être mis en évidence pour le frittage du spinelle pur (trajectoire de frittage, mécanisme de densification et évolution de la porosité identiques), ces travaux ont démontré que l’impact de dopants pouvait être amplifié en présence du rayonnement micro-ondes. Ainsi, un décalage des courbes de retrait vers les basses températures a été observé lors du frittage micro-ondes du spinelle dopé avec TiO2 et MgO. L'existence d'un couplage particulier entre les défauts ponctuels chargés (lacunes, cations interstitiels) et le champ électrique pourrait être à l'origine de ce phénomène. Ces travaux de thèse ont également démontré la faisabilité de fritter des pièces de spinelle carrées de grandes dimensions (< 65 mm) compatibles avec un post-traitement HIP, en vue d'obtenir des pièces transparentes. Pour cela, un four micro-ondes monomode 915 MHz a été automatisé et une cellule de frittage adaptée a été développée. A l'issue du traitement HIP, les pièces ont présenté une transparence et des propriétés mécaniques (dureté; ténacité) comparables à celles des pièces pré frittées par voie conventionnelle. / The elaboration of transparent ceramics (no porosity, no second phase) requires a strict control of all steps of the process (synthesis, shaping, sintering). As a result, the industrialization of a reproducible process is still difficult to achieve. In this context, this thesis has focused on developing and evaluating the ability of the microwave sintering process to improve the robustness of the transparent spinel elaboration process.The set-up of an optical dilatometer and a new original calibration method, based of melting of different oxides, allowed to characterize the microwave sintering with a greater confidence. Even if no microwave effect has been observed on the sintering of pure spinel (identical sintering trajectory, densification mechanism and porosity evolution), this work has shown an amplification of the impact of dopants during microwave sintering. A shift of the shrinkage curves towards the low temperatures was observed during the microwave sintering of the spinel doped with TiO2 and MgO. The existence of a particular interaction between charged point defects (vacancies, interstitial cations) and the electric field could explain this phenomenon.This work thesis has shown also the feasibility of sintering of large square spinel pieces (< 65 mm) compatible with post treatment HIP in order to produce transparent ceramics. For this purpose, the microwave system working at 915 MHz was automatized and a new sintering configuration was developed. After a post-treatment, the transparency and mechanical properties (hardness; tenacity) of microwave pre-sintered samples were comparable with those of samples sintered by conventional heating.

Ce travail porte sur l’élaboration de céramiques transparentes composites à base de grenats d’yttrium et d’aluminium (Nd:YAG) avec différents ratios stœchiométriques (Nd+Y)/Al compris entre 0,40 et 0,70, autour du ratio correspondant à la composition stœchiométrique du Nd:YAG ((Nd+Y)/Al = 0,6000) par frittage-réaction sous vide. La mise en forme a été effectué par coulage sous pression de suspensions stables et homogènes de mélanges Al2O3-Y2O3-Nd2O3. L’étude des propriétés microstructurales, thermiques et optiques de ces céramiques a permis de mettre en évidence l’influence du ratio (Nd+Y)/Al sur les cinétiques de formation de la phase grenat et de densification du matériau ainsi que sur leurs propriétés optiques. Ainsi, il apparaît que pour des céramiques avec un ratio supérieur à 0,6000, correspondant à un matériau enrichi en yttrium, les cinétiques précédemment évoquées sont diminuées mais les propriétés de transparence et lasers apparaissent moins dégradées, contrairement au cas de céramiques enrichies en aluminium ((Nd+Y)/Al < 0,6000). De plus, l’étude de mélanges pulvérulents Nd:YAP-Al2O3 a permis de mettre en évidence un mécanisme de formation de la phase Nd:YAG suggérant l’existence d’une réaction solide-gaz avec évaporation-condensation de la phase réactive aluminée. Enfin, la faisabilité de céramiques de Nd:YAG à haut taux de dopage (4 % at.) a permis de montrer l’intérêt de ces matériaux dans la génération de propriétés optiques non linéaires du troisième ordre, particulièrement le phénomène d’autofocalisation de faisceaux lumineux par effet Kerr. / This work is devoted to the elaboration of yttrium and aluminum garnets-based transparent composite ceramics with different (Nd+Y)/Al stoichiometric ratios ranged from 0.40 to 0.70, around the ratio corresponding to the Nd:YAG stoichiometric composition ((Nd+Y)/Al = 0.6000) by under-vacuum reactive-sintering. Pressure-casting of stable and homogeneous suspensions of mixing Al2O3-Y2O3-Nd2O3 was achieved. Study of microstructural, thermal and optical properties of these ceramics has made it possible to highlight the influence of (Nd+Y)/Al ratio on garnet phase formation and densification kinetics, and on optical properties. Thus, it appears that for ceramic with a ratio higher than 0.6000, corresponding to an yttrium-rich sample, the previously mentioned kinetics are decreased but transparence and lasers properties are less degraded, contrary to aluminum-rich ceramics ((Nd+Y)/Al < 0.6000). Moreover, study of Nd:YAP-Al2O3 powders mixing brings out Nd:YAG phase formation mechanism, suggesting the existence of solid-gas reaction with evaporation-condensation of aluminum-rich reactive phase. Finally, feasibility of Nd:YAG ceramics with high dopant content (4 at. %) has shown the interest of these materials in order to generate third-order nonlinear optical properties, especially self-focusing phenomenon of light beams by Kerr effect.

The presented diploma thesis is focused on the preparation and properties of transparent polycrystalline ceramic materials based on Al2O3. Theoretically, the most important technological aspects of the processing of these materials are presented. Detailed attention is given to transparent Al2O3 polycrystalline ceramics doped with rare earth elements. The influence of microstructural parameters on the optical properties (represented by RIT) is investigated on Al2O3 samples doped and codoped with dysprosium, terbium and chromium. A significant effect of the average grain size on the light transmittance of all samples is observed. The highest RIT = 55 % (measured by a laser beam with a wavelength of 632,8 nm) was achieved by an optimized preparation process for a sample doped with 0,05 at. % of dysprosium. For all samples photoluminescent properties are also analysed. The photoluminescent emission spectra correspond to the activation of doping elements. In case of the terbium and chromium codoped samples, the differences in the activation of individual dopants depending on different excitation wavelengths were demonstrated, resulting in different colour emissions for different excitation wavelengths.

Alumina based transparent ceramic bodies were prepared within this diploma thesis by the gel casting process followed by presintering to closed porosity stage with subsequent hot isostatic pressing. The problematic drying of large bodies was solved by means of careful temperature and relative humidity control and by osmotic drying. Almost perfectly dense ceramics were achieved thanks to colloidal processing of TM-DAR and TM-UF ceramic powders providing a final structure with grain size of 381 nm, resp. 302 nm. High real in-line transmission of 72,3 % was achieved at wavelength of 632,8 nm and thickness of 0,8 mm. Among mechanical properties high values of hardness HV10 = 22,5 GPa, fracture toughness KIC = 3,99 MPam0,5, Young’s modulus E = 400 GPa a bending strength o = 494 MPa were achieved.

<p>Yttrium aluminum garnet (YAG) is a transparent ceramic with various applications, including solid-state lasers, infrared transparent windows, armors, and scintillation crystals. Recently, uranium (U) doped YAG has gained interest as a scintillation material for neutron detection. The principle of neutron detection using U:YAG is that under neutron bombardment, the U atoms within the YAG will fission, providing excitation energy to surrounding U atoms in order to emit photons. As this material is rarely reported, an investigation into the fabrication procedure of this material is conducted. Powder fabrication methods are investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The sintering of the fabricated powders is then investigated by various experimental techniques. Characterization of the sintered samples included optical microscopy, Archimedes density measurements, and XRD.</p>

京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第20460号 / 人博第810号 / 新制||人||194(附属図書館) / 28||人博||810(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 田部 勢津久, 教授 加藤 立久, 教授 吉田 寿雄 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

La réalisation de céramiques transparentes de type Er:YAG pour application laser nécessite une transparence parfaite ce qui implique une grande qualité de la poudre utilisée et une parfaite maîtrise des procédés de fabrication. Afin d’obtenir une céramique transparente, la première partie de cette thèse a consisté à corriger le principal défaut de deux poudres de YAG expérimentales. Dans la première poudre, un taux de soufre élevé a été mesuré et l’objectif a été d’éliminer cette impureté par des traitements chimiques et thermiques, tout en gardant les caractéristiques structurales et granulométriques de la poudre de départ. La seconde poudre présentait un déficit en yttrium et le but a été de corriger ce déséquilibre par l’ajout d’yttrine. Dans un deuxième temps, afin de s’affranchir des problèmes de non-reproductibilité de la qualité des poudres commerciales de YAG, la possibilité d’obtenir des céramiques transparentes YAG par frittage réactif à partir de poudres d’alumine et d’yttrine a été étudiée. Lors de cette étude, le mélange, la stoechiométrie, la compaction, la densification et les transformations de phase ont été suivis dans le but de réaliser une carte de frittage de ce mélange. La dernière étude concerne l’obtention de céramiques transparentes à gradient de dopage suivant trois approches ayant pour point commun l’emploi de la technique de frittage SPS. La première a consisté en l’assemblage de céramiques déjà totalement densifiées, la deuxième, de céramiques pré-frittées et enfin, la dernière, d’un empilement de lits de poudres. Les mesures de diffusion des ions Erbium à travers l’interface ont permis de comparer ces différentes approches. / The realization of transparent Er:YAG ceramics for laser application requires a perfect transparency that implies a high quality of the used powder and a perfect control of the manufacturing processes. However, the quality of the starting powder is sometimes insufficient and its characteristics are not suitable in terms of stoichiometry, impurities or particle morphology. In this case, a pre-treatment of the powder and the use of sintering aids are necessary to obtain transparency. In order to prepare transparent ceramics, the first part of this work consisted in correcting the main defects of two experimental YAG powders. In the first powder, a high level of sulfur was measured and the objective was to eliminate this impurity by chemical and thermal treatments, while keeping the structural characteristics and particle size of the starting powder. In the second powder, the measured stoichiometry showed an yttrium deficiency of 5.3 mol% and the purpose was to correct the Y/Al ratio by addition of yttria. In a second part, in order to overcome the problems of non-reproducibility of the quality of YAG commercial powders, the possibility of obtaining YAG transparent ceramics by reactive sintering from alumina and yttria powders was investigated. The last part of this study concerned the development of transparent ceramics with doping gradients by three approaches having in common the use of SPS sintering. The first involved the assembly of fully dense ceramics; the second, pre-sintered ceramics and finally, the last approach a stack of powder layers. The measurement of Erbium ion diffusion through the interface made it possible to compare these different approaches.

Les céramiques polycristallines transparentes de YAG (Yttrium Aluminium Garnet, Y3Al5O12) et de YAG dopé par des lanthanides (Nd, Er, Ho, etc.) ont des propriétés optiques comparables aux monocristaux et peuvent être utilisées comme milieu laser solide dans les lasers solides à haute capacité calorifique. L’utilisation de ces céramiques polycristallines transparentes présente de nombreux avantages comparés aux monocristaux. Ces matériaux ont une meilleure conductivité thermique et sont fabriqués à plus faible coût tout en présentant des propriétés mécaniques améliorées et ce, sur des pièces de plus grandes dimensions. De plus, il est possible d’atteindre de plus forts taux de dopage avec une répartition uniforme du dopant. Le dopage du YAG par l’erbium (0.25 %at.) permet une émission laser « eye-safe » de 1645nm. De plus, un faible taux de dopage permet d’éviter le phénomène d’upconversion lors de l’effet laser.Les conditions pour obtenir la transparence sont, entre autres, l’absence de défauts, une très grande pureté (>99.9%), une répartition de taille de grains homogène et une densité très élevée (>99.9%).Les céramiques transparentes sont obtenues par la voie métallurgie des poudres. La synthèse par voie chimique (co-précipitation, sol-gel, voie hydrothermale…) permet la production de poudres très pures, avec une taille de particules homogène et nanométrique, comparée à la synthèse par voie mécanique (broyage d’oxydes). Le frittage SPS (Spark Plasma Sintering) permet quant à lui une densification rapide, à plus basse température, empêchant ainsi une croissance excessive et anormale des grains lors de la densification. L’application d’un courant électrique de forte intensité associée à une charge uniaxiale permet d’accélerer la cinétique de frittage comparé aux méthodes de frittage conventionelles.Ce travail porte sur l’élaboration de céramiques polycristallines transparentes Er:YAG par la voie métallurgie des poudres. La synthèse de poudre est réalisée par co-précipitation inverse d’une solution de nitrates dans l’hydrogénocarbonate d’ammonium. L’influence des paramètres de synthèse tels que le pH, la concentration, le temps de maturation ou encore le cycle de calcination a été étudiée. Après optimisation des conditions de synthèse, des particules d’Er:YAG pur présentant une taille moyenne de 50nm ont été obtenues. L’étude des mécanismes réactionnels a été menée en associant différentes techniques de caractérisations en température telles que la spectrométrie IR, la diffraction des rayons X, ainsi que des analyses thermo-gravimétriques et différentielles. La formation de la phase YAG à 1050°C passe par la formation d’une phase intermédiaire, le YAP (Yttrium Aluminium Perovskite, YAlO3) à 900°C.Les poudres synthétisées ont ensuite été frittées par frittage flash SPS. L’étude de l’influence du cycle de frittage (température, charge, rampe, maintien) sur la microstructure et son optimisation a été réalisée à partir de poudre commerciale et a permis l’obtention de céramiques transparentes de diamètre 30mm et d’épaisseur 3mm. Un changement d’échelle a également été réalisé permettant la réalisation d’échantillons de diamètre 60mm d’une part, et d’épaisseur 6mm d’autre part / Yttrium aluminium garnet (YAG, Y3Al5O12) transparent ceramics have attracted much attention since it can replace single crystals as host materials in solid state heat capacity lasers. These polycrystalline ceramics present improved mechanical and spectroscopic properties, as well as a better heat conductivity, lower fabrication costs for larger size materials. Furthermore, it is possible to reach higher doping concentrations as well a uniform distribution. Doping YAG with Erbium (Er:YAG) allows eye-safe emission at 1645nm. Moreover, a low doping rate (0.5%at.) enables upconversion process during laser operation. Conditions for transparency are amongst others, the absence of defects, a high purity (>99.9%), an homogeneous grain size as well as a high density (>99.9%).Transparent polycrystalline ceramics can be obtained by powder metallurgy route. Powders, synthesized by chemical reactions such as sol-gel process, co-precipitation or hydrothermal methods, present some advantages like high purity, homogeneity and nano-sized particles compared to those obtained by solid-state reactions. A recent process called Spark Plasma Sintering (SPS) is presented to be a promising technique for the densification of nanostructured materials. Indeed, high current and pressure allow sintering at lower temperatures in shorter sintering time than in regular processes. Besides, rapid heating enables to limit excessive grain growth.In this study, Er:YAG nanopowders have been synthesized by co-precipitation using nitrates as precursors and ammonium hydrogen carbonate as precipitant. The influence of precipitation parameters such as pH, concentration, aging time, or even calcination temperature, has been studied. Er:YAG nanoparticles, with an average grain size of 30nm have been successfully synthesized. The reaction mechanisms have been investigated using different techniques such as infrared spectroscopy, x-ray diffraction, thermal analyses… The YAG phase is formed around 1050°C passing through an intermediate phase called YAP (Yttrium Aluminium Perovskite, YAlO3) at 900°C.Synthesized and commercial powders have been sintered to transparency using SPS device. Optimisation of the sintering conditions (temperature, load, heating rate, dwell time) have been realized using commercial powder. Transparent polycrystalline ceramic specimens with a 30mm diameter and 3mm thickness have been successfully obtained. A scale-up study enabled to produce samples with a diameter up to 60mm and also with 6mm thickness

Recentemente, grande interesse tem sido demonstrado por cerâmicas transparentes dopadas com íons terras raras trivalentes, como meios ativos para lasers na região espectral do infravermelho próximo. Em particular, cerâmicas dopadas com altas concentrações de Nd3+ e Yb3+ são muito estudadas pela possibilidade de gerar emissão laser de alta potência em torno de 1,0 mm. Embora a cerâmica transparente de titanato zirconato de chumbo e lantânio (PLZT), com composição La/ Zr/Ti = 9/65/35, seja originalmente reconhecida por suas propriedades ferroelétricas e eletro-ópticas, a mesma também apresenta características interessantes como matriz hospedeira de íons oticamente ativos. Recentemente, de Camargo et al. realizaram vários estudos espectroscópicos que comprovam a potencialidade laser de amostras dopadas com Yb3+, Er3+, Tm3+ e em especial Nd3+. Apesar de a cerâmica PLZT:Nd ser a mais promissora, se comparada a líder de mercado YAG:Nd (sistema ítrio-alumínio garnet dopado com neodímio), ainda não foi possível obter ação laser da primeira, devido à presença de fases espúrias (imperceptíveis a olho nu), que comprometem a qualidade óptica do material, especialmente para concentrações de dopagem maiores que 1,0% peso de Nd2O3. Uma vez que a qualidade estrutural tem implicação direta na qualidade óptica/espectroscópica de materiais ópticos, faz-se necessário estender os estudos visando otimizar a obtenção de amostras transparentes com mais altos níveis de dopagem. Neste trabalho apresenta-se um método alternativo para a dopagem da matriz PLZT com os íons TR = Nd3+ e Yb3+, e utiliza-se de várias técnicas (DR-X, DTA-TG, FT-IR, Raman, RMN e Luminescência), para caracterizar os compostos precursores e/ou produtos. O novo método baseia-se na obtenção prévia de óxidos precursores dopados, seguida da utilização destes para o preparo das cerâmicas PLZT:TR. As caracterizações foram conduzidas em função da concentração de dopantes (0,1 4,0% peso TR2O3), comparativamente ao método de dopagem convencional utilizado nos trabalhos anteriores. A espectroscopia de ressonância magnética nuclear em sólidos em 207Pb, mostrou-se uma ferramenta bastante útil na elucidação de questões estruturais desses sistemas tão complexos. Como os íons paramagnéticos Nd3+ e Yb3+ não podem ser diretamente acessados por RMN, a estratégia para caracterizar suas distribuições espaciais foi investigar suas respectivas mímicas diamagnéticas Y3+ e Sc3+ (núcleos 45Sc e 89Y). Resultados de DR-X apresentam menor formação de fase secundária nas amostras preparadas via método alternativo, sendo identificado as fases secundárias como (La,Nd)2(Zr,Ti)2O7 (estrutura do tipo pirocloro), ZrO2 em fase parcialmente monoclínica e cúbica e ZrO2 em fase cúbica, das amostras dopadas com Nd3+, Y3+ e Yb3+, respectivamente. De acordo com os resultados de DR-X, experimentos de RMN permitiram melhor avaliação quanto a inserção do íon dopante a medida que há formação de fase secundária e mostraram que a inserção dos íons dopantes é homogênea, bem como resultados de luminescência, com o limite de solubilidade do íon dopante sempre menor do que o necessário para que seja observado supressão da luminescência dos íons emissores. / In recent years, there has been a great interest for rare-earth (RE) doped transparent ceramics as near-infrared laser active media. Particularly, Nd3+ and Yb3+-doped ceramics are of special interest due to the possibility of generating high power emissions at around 1.0 mm. Even though lead lanthanum zirconate titanate (PLZT) ceramics, with composition La/Zr/Ti = 9/65/35, are mostly known by their ferroelectric and electro-optic properties, recent works by de Camargo et al. have also indicated their potentiality as laser active media. In this regard, the most promising system is PLZT:Nd (as compared to YAG:Nd - neodymium-doped yttrium aluminium garnet), however, laser action of the former has not yet been possible, the reason lying in the presence of secondary phases (invisible to the naked eye) that compromise the optical quality of the ceramics, especially for samples with concentration higher than 1.0 wt% Nd2O3. Since the structural quality of samples has a direct implication on their spectroscopic and optical qualities, the goals pursued in this work are to present means to obtain highly transparent samples with higher incorporation of dopants, as well as to understand some fundamental questions regarding the microstructure of PLZT:RE ceramics. Thus, an alternative method, based on the obtainment of RE-doped precursor oxides, is presented for the synthesis of PLZT:RE and several techniques (XRD, DTA-TG, FT-IR, Raman, NMR and Luminescence) are used to characterize the samples, as a function of doping concentration (0,1 4,0 wt% RE2O3). These studies are done in comparison to the conventional method used in previous works. Solid state NMR spectroscopy of 207Pb proved to be a very useful tool for the understanding of these complex systems. Because Nd3+ and Yb3+ are paramagnetic and thus inaccessible by NMR, the strategy used for the characterization of their spatial distribution was to study samples doped with their respective diamagnetic mimics Sc3+ and Y3+ (45Sc and 89Y nuclei). XRD results have shown formation of less secondary phase for samples prepared by alternative method, being identified as secondary phase pyrochlore structure (La,Nd)2(Zr,Ti)2O7, partially monoclinic/cubic ZrO2 and cubic ZrO2 of the samples doped with Nd3+, Y3+ and Yb3+ respectively. NMR measurements allowed to make proposals about dopant ion insertion while secondary phase is formed and showed homogeneous distribution of dopant into the matrix, aswell luminescence measurements with maximum dopant solubility being less than enough to show any suppression of luminescence.