In Siedewasserreaktoren ist ein Boreinspeisesystem diversitär wirkend zur Reaktorschnellabschaltung installiert. Dieses System garantiert, dass der Reaktor beim Versagen des Schnellabschaltesystems in einen unterkritischen Zustand überführt werden kann. Der aufgrund der Nachzerfallsleistung entweichende Dampf trägt jedoch ständig einen Teil des eingespeisten Bors in Form von Borsäure mit sich. Da dieser Prozess bisher nicht quantifiziert wurde, ist somit das Eintreten einer Rekrititkalität während der Transiente ohne weitere Untersuchungen nicht auszuschließen. In der vorliegenden Arbeit erfolgt die Erstellung einer fundierten Datenbasis zur Quantifizierung des Borverlusts an verschiedenen Betriebspunkten. Dazu stehen nach vorheriger Konstruktion und Inbetriebnahme zwei Versuchsanlagen zur Verfügung, ein Versuchsautoklav und der Siedewasserreaktor-Simulator BORAN. Das in diesen Versuchsanlagen enthaltene und als Kühlmedium genutzte entionisierte Wasser wird wie bei einem Siedewasserreaktor mit einer hochkonzentrierten Lösung der Borverbindung Dinatrium-Pentaborat-Dekahydrat versetzt. Für weiterführende Untersuchungen findet auch Borsäure Verwendung. Die Bestimmung des Borgehalts der Kondensate des entwichenen Dampfes erfolgt mit Massenspektrometrie mit induktiv gekoppeltem Plasma (ICP-MS). Die durch Variation von Borkonzentration, Temperatur, pH-Wert und Volumendampfgehalt erzeugten Messdaten fließen in einem Flüchtigkeitsmodell in Form einer empirischen Gleichung zusammen, welches in den Thermohydraulikcode ATHLET implementiert wird. Experimente am SWR-Simulator BORAN und entsprechende Rechnungen mit dem modifizierten Code ATHLET von Langzeit-Deborierungstransienten bei unterschiedlichen Randbedingungen bestätigen das Flüchtigkeitsmodell. Gleichzeitig erfolgt mittels dieser Experimente die Validierung des Modells im ATHLET mit hinreichender Genauigkeit. Mit den Ergebnissen aus Rechnungen und Experimenten wird das Boreinspeisesystem in seiner aktuellen Konfiguration bewertet und mit zukünftigen Konzepten verglichen. Schlussendlich erfolgt der Nachweis, dass die Funktionalität des Boreinspeisesystem aus dem Blickwinkel der durchgeführten Analysen, trotz der nachgewiesenen Borflüchtigkeit, die Forderungen der KTA 3103 erfüllt und aufgrund der nachgewiesenen Borflüchtigkeit binnen der ersten beiden Stunden der Transiente keine Rekritikalität verursacht wird.:1 Einleitung und Motivation 1 A Theoretische Vorbetrachtung 2 Die Borchemie 9 2.1 Bor 9 2.2 Borverbindungen 9 2.3 Beeinflussung der Ionenzusammensetzung gelöster Borat-Ionen 15 2.4 Flüchtigkeit von Borsäure und Boraten 18 2.5 Veränderungen der Oberflächenspannung von Wasser durch Borverbindungen 23 3 Probenpräparation 24 4 RAMAN-Spektroskopie und Thermogravimetrie / Differenzthermoanalyse 25 B Beschreibung der Versuchsanlagen und des Simulationsprogramms 5 Versuchsanlage – Autoklav 29 6 Versuchsanlage – Umlaufschleife BORAN 31 7 Zweiphasenmesstechnik und Phasenschlupf 40 8 Leitfähigkeit und pH-Messungen an Borlösungen 46 9 Konzentrationsbestimmung 48 10 Konzentrationsmesssystem in der Umlaufschleife BORAN 51 C Messwerteerfassung und Modellbildung 11 Borausbreitung in einphasiger und zweiphasiger Strömung 55 12 Flüchtigkeit des Bors mit Wasserdampf 57 12.1 Vorbetrachtungen 57 12.2 Flüchtigkeitsmessungen am Autoklav 59 12.2.1 Einfluss von Substanz, Konzentration und Temperatur 59 12.2.2 Einfluss vom pH-Wert 62 12.2.3 Einfluss des Füllstandes 63 12.3 Flüchtigkeitsmessungen an der BORAN – Anlage 64 12.3.1 Vorteile gegenüber dem Autoklav 64 12.3.2 Einfluss von Temperatur und Dampfgehalt 64 12.3.3 Einfluss des Massenstroms 67 12.3.4 Einfluss des pH-Wertes 70 12.3.5 Transiente Messpunkte 71 13 Modellbildung – Beschreibung über empirische Gleichungen 73 14 Borflüchtigkeit mit eingeperltem Dampf oder Luft 77 14.1 Einperlung von Dampf in die BORAN – Anlage 77 14.2 Lufteinperlung in borsaure Lösung in Lufteinperlanlage 81 15 Ergebnisvergleich von BORAN – Anlage und Autoklav 84 16 Einordnung der Experimente in das Flüchtigkeitsmodell 85 17 Zusammenfassende Ergebnisdarstellung – Diskussion 87 17.1 Volumendampfgehalt und Phasengrenzflächendichte 89 17.2 Bormassenstromdichte 91 D Simulationen mit ATHLET und Deborierung 18 ATHLET – ein Simulationsprogramm der Thermohydraulik 93 18.1 Einführung in das Simulationsprogramm 93 18.2 Erstellen und Anpassen des Eingabedatensatzes für BORAN 96 19 Modifikation des ATHLETs für Deborierungsrechnungen 99 20 Flüchtigkeitsverhalten bei zeitlich langem Ausdampfen 101 21 Bewertung der bisherigen Ergebnisse 103 E Bezug zur Realanlage 22 Abschätzung des Borverlustes bei Transienten 105 23 Möglichkeiten der Reduktion der Borflüchtigkeit 107 24 Zukünftige Einspeisekonzepte 108 F Zusammenfassung 25 Zusammenfassung der Ergebnisse 113 26 Danksagung 117 27 Quellen- und Literaturverzeichnis 119 28 Tabellenverzeichnis 125 29 Abbildungsverzeichnis 126 G Anhänge 30 Anhang 1 Exakte Berechnung des pH-Wertes der Lösung beim Erwärmen 133 31 Anhang 2 ATHLET-Rechnung für Autoklav 135 32 Anhang 3 Konstruktionsbeschreibung der Versuchsanlage BORAN 137 / In boiling water reactors a boron injection system as an alternative system is installed to guarantee that the reactor shut down in case of a total or partial ATWS accident. Because of the heat generated by the fission products after shutting down a part of the injected boron is evaporated as boron acid. This process is not characterized quantitatively yet. This is the reason that the incidence of recriticality during a transient cannot be excluded without further research. In the following studies a funded database quantifying the loss of boron is established. The volatility of the boron solution was measured by experiments in a small autoclave and in a boiling water reactor simulator called BORAN after construction. The deionised water used as coolant in the facilities will be enriched with boron by a high concentrated solution of Disodium-Pentaborate-Decahydrate. The measurement of the boron concentration in the condensates of the exhausted vapour is carried out by inductively-coupled-plasma mass-spectrometry (ICP-MS). For additional analysis boron acid is also used. The boron concentration in the vapour mainly depends on the temperature and void fraction of the two-phase-flow. This volatility model in form of an empiric equation is implemented in the thermo hydraulic ATHLET-code. Furthermore the reason of the volatility of the analysed solutions will be discussed within a chemical and physical background. Experiments at the BORAN facility and corresponding calculation with the modified ATHLET-code of long time deboration transients with different boundary conditions prove the volatility model. Thereby the code will be validated with sufficient accuracy. The modified code with an adapted Input-Dataset provides the possibility to calculate transients with the loss of boron. With the consideration of the volatility the demand of the KTA-rule 3103 on the Boron injection system is also grantable.:1 Einleitung und Motivation 1 A Theoretische Vorbetrachtung 2 Die Borchemie 9 2.1 Bor 9 2.2 Borverbindungen 9 2.3 Beeinflussung der Ionenzusammensetzung gelöster Borat-Ionen 15 2.4 Flüchtigkeit von Borsäure und Boraten 18 2.5 Veränderungen der Oberflächenspannung von Wasser durch Borverbindungen 23 3 Probenpräparation 24 4 RAMAN-Spektroskopie und Thermogravimetrie / Differenzthermoanalyse 25 B Beschreibung der Versuchsanlagen und des Simulationsprogramms 5 Versuchsanlage – Autoklav 29 6 Versuchsanlage – Umlaufschleife BORAN 31 7 Zweiphasenmesstechnik und Phasenschlupf 40 8 Leitfähigkeit und pH-Messungen an Borlösungen 46 9 Konzentrationsbestimmung 48 10 Konzentrationsmesssystem in der Umlaufschleife BORAN 51 C Messwerteerfassung und Modellbildung 11 Borausbreitung in einphasiger und zweiphasiger Strömung 55 12 Flüchtigkeit des Bors mit Wasserdampf 57 12.1 Vorbetrachtungen 57 12.2 Flüchtigkeitsmessungen am Autoklav 59 12.2.1 Einfluss von Substanz, Konzentration und Temperatur 59 12.2.2 Einfluss vom pH-Wert 62 12.2.3 Einfluss des Füllstandes 63 12.3 Flüchtigkeitsmessungen an der BORAN – Anlage 64 12.3.1 Vorteile gegenüber dem Autoklav 64 12.3.2 Einfluss von Temperatur und Dampfgehalt 64 12.3.3 Einfluss des Massenstroms 67 12.3.4 Einfluss des pH-Wertes 70 12.3.5 Transiente Messpunkte 71 13 Modellbildung – Beschreibung über empirische Gleichungen 73 14 Borflüchtigkeit mit eingeperltem Dampf oder Luft 77 14.1 Einperlung von Dampf in die BORAN – Anlage 77 14.2 Lufteinperlung in borsaure Lösung in Lufteinperlanlage 81 15 Ergebnisvergleich von BORAN – Anlage und Autoklav 84 16 Einordnung der Experimente in das Flüchtigkeitsmodell 85 17 Zusammenfassende Ergebnisdarstellung – Diskussion 87 17.1 Volumendampfgehalt und Phasengrenzflächendichte 89 17.2 Bormassenstromdichte 91 D Simulationen mit ATHLET und Deborierung 18 ATHLET – ein Simulationsprogramm der Thermohydraulik 93 18.1 Einführung in das Simulationsprogramm 93 18.2 Erstellen und Anpassen des Eingabedatensatzes für BORAN 96 19 Modifikation des ATHLETs für Deborierungsrechnungen 99 20 Flüchtigkeitsverhalten bei zeitlich langem Ausdampfen 101 21 Bewertung der bisherigen Ergebnisse 103 E Bezug zur Realanlage 22 Abschätzung des Borverlustes bei Transienten 105 23 Möglichkeiten der Reduktion der Borflüchtigkeit 107 24 Zukünftige Einspeisekonzepte 108 F Zusammenfassung 25 Zusammenfassung der Ergebnisse 113 26 Danksagung 117 27 Quellen- und Literaturverzeichnis 119 28 Tabellenverzeichnis 125 29 Abbildungsverzeichnis 126 G Anhänge 30 Anhang 1 Exakte Berechnung des pH-Wertes der Lösung beim Erwärmen 133 31 Anhang 2 ATHLET-Rechnung für Autoklav 135 32 Anhang 3 Konstruktionsbeschreibung der Versuchsanlage BORAN 137

Optical properties of bismuth borate are measured for the composition range x Bi2O3 (1-x) B2O3, 0.25 < x < 0.65. The refractive indices increase as the bismuth content is increasing. Also the ultraviolet absorption edge was shown to shift to longer wavelengths. From these measurements a generalized Sellmeier formula was derived. Applying heat treatments to the prepared bismuth borate glasses in order to obtain glass ceramics leads in most cases to surface nucleation. It was proved that dopants increase the number of nucleating sites on the surfaces. On erbium-doped samples absorption and luminescence measurements were made. The Judd-Ofelt analysis revealed comparably high Judd-Ofelt coefficients. All coefficients were shown to decrease as the Bi2O3 content increases. The luminescence at 1550 nm reveals a broad and flat band which is narrowing with the increase in Bi2O3 content. The green upconversion was observed and the temporal behavior of the emission at 550 nm was investigated. The absorption and emission spectra of chromium-doped bismuth borate glasses were measured. On surface crystallized glasses, for x = 0.5 Bi2O3 and high chromium content, luminescence of chromate (CrO2-4) ion doped BiBO3 microcrystals was observed. Strontium barium niobate microcrystals embedded in strontium barium borate matrix were obtained by spontaneous nucleation in the melt and rapid quenching. Optical properties of Pb2B5O9Br based glass were also investigated. The heat treatment applied leads to the formation of small nanocrystals inside the glass.

Pure samples of colorless, air-stable Ba(BO2OH) crystals were obtained from Ba(NO3)2 and H3BO3 under the ultra-alkaline conditions of a KOH hydroflux at about 250 °C. The product formation depends on the water-base molar ratio and the molar ratio of the starting materials. B(OH)3 acts as a proton donor (Brønsted acid) rather than a hydroxide acceptor (Lewis acid). Ba(BO2OH) crystallizes in the non-centrosymmetric orthorhombic space group P212121. Hydrogen bonds connect the almost planar (BO2OH)2− anions, which are isostructural to HCO3−, into a syndiotactic chain. IR and Raman spectroscopy confirm the presence of hydroxide groups, which are involved in weak hydrogen bonds. Upon heating in air to about 450 °C, Ba(BO2OH) dehydrates to Ba2B2O5. Moreover, the non-centrosymmetric structure of Ba(BO2OH) crystals was verified with power-dependent confocal Second Harmonic Generation (SHG) microscopy indicating large conversion efficiencies in ambient atmosphere.

Pursuing the development and implementation of novel synthesis techniques to produce nanostructures with an interesting set of properties is a goal that advances the frontiers of nanotechnology. Also of fundamental importance is to revisit well-established synthesis techniques employing a new set of materials as precursors, substrates and catalysts. Fundamental breakthroughs in the field of nanotechnology can be achieved by developing new synthesis procedures as well as by adapting known procedures to new materials. This thesis focuses on both kinds of experiments. A variant of chemical vapor deposition (CVD) has been used to produce Al5BO9 nanowires out of sapphire wafers without the need of a catalyst material. The novelty of the work relies on the formation mechanism of the Al5BO9 nanowires. Essentially, the process can be described as a large-scale topological transformation taking place on the substrate’s surface as its chemical composition changes due to the arrival of precursor molecules. Dense mats of Al5BO9 nanowires cover large areas of the substrate that were previously relatively flat. The process is enhanced by a high temperature and the presence of pre-existing superficial defects (cracks, terraces, etc.) on the substrates. Al5BO9 nanowires as well as B/BOX nanowires and BOX nanotubes were also produced via a novel in-situ electron beam-induced synthesis technique. The process was carried out at room temperature and inside a transmission electron microscope. Au nanoparticles were used as catalyst for the case of B/BOX nanowires and BOX nanotubes, while the Al5BO9 nanowires were synthesized without the need of a catalyst material. The formation and growth of the nanostructures is solely driven by the electron beam. The growth mechanism of the B/BOX nanowires and BOX nanotubes relies on interplay between electrostatic charging of the precursor material (to produce and transport feedstock material) and electron stimulated desorption of oxygen which is able to activate the catalytic properties of the Au nanoparticles. For the case Al5BO9 nanowires a nucleation process based on massive atomic rearrangement in the precursor is instigated by the e-beam, afterwards, the length of some of the nanowires can be extended by a mechanism analogous to that of the growth of the B/BOX nanowires.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Este trabalho teve como principal objetivo o estudo sistemático da obtenção da fase beta-BaB204 (beta-BBO) a partir de uma fase vítrea do sistema BaO-B2O3-TiO2. Foram estudadas amostras contendo entre 4 e 16% de TiO2. A avaliação das propriedades térmicas, estruturais e microestruturais das amostras foi realizada empregando as técnicas de Analise Térmica Diferencial (DTA), Difração de Raios-X (DRX), Microscopia óptica (MO), Microscopia Eletrônica de Varredura (MEV), Espectroscopia Raman, Absorção e Transmissão óptica no Infravermelho, Espectroscopia de Absorção de Raios-X (XAS) e Ressonância Magnética Nuclear (RMN). O coeficiente de Geração de Segundo Harmônico (GSH) foi obtido através das medidas do loci de casamento de fase e da Franja de Maker. O estudo do processo de cristalização revelou que em todas as amostras prevaleceu o mecanismo de cristalização superficial. Nas amostras contendo 4 e 8% de TiO2 foi observada a cristalização da fase beta-BBO enquanto que nas amostras contendo 15 e 16% de TiO2, foi observado que o processo de cristalização se inicia pela fase BaTi(BO3)2 e que somente após longos tempos de tratamento, a fase beta-BBO se toma a fase predominante. A identificação da fase BaTi(BO3) somente foi possível com a utilização da técnica de Espectroscopia Raman. O estudo da estrutura local através das técnicas de XAS e RMN mostrou que a estrutura local ao redor dos átomos de titânio, bário e boro nas amostras cristalizadas é pouco afetada quando a quantidade de TiO2 passa de 4 para 16%. A análise dos resultados da medida de geração de segundo harmônico mostrou que nas amostras contendo uma camada da superfície cristalizada, o valor do coeficiente de geração de segundo harmônico (deff) é equivalente ao do quartzo monocristalino e na amostra contendo 16% de TiO2, corresponde a 70% do valor observado na fase beta-BBO em sua forma monocristalina / This work consists of a systematic study of the beta-BaB2O4 (beta-BBO) crystalline phase obtained from the BaO-B2O3-TiO2 glass system containing amounts of titanium varying from 4 to 16 mol%. The thermal, structural and microstructural properties of the samples were evaluated by the following techniques: Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Raman Spectroscopy, Infrared Optical Absorption Spectroscopy, X-Ray Absorption Spectroscopy (XAS) and Nuclear Magnetic Resonance (NMR). The Second Harmonic Generation (SHG) coefficient (def) was obtained from the phase matching Loci and Maker fringe curves. A study of the crystallization process revealed that the surface crystallization mechanism predominated in each of the samples. Only the beta-BBO phase was observed in the samples containing 4 and 8 mol% of TiO2. However, in the samples containing 15 and 16 mol% of TiO2, crystallization of the BaTi(BO3)2 occurred first and was followed by crystallization of the P-BBO phase, which subsequently became the main phase as the period of heat treatment increased. The identification of the BaTi(BO3)2 phase in the early stage of the crystallization process was only possible by using the Raman spectroscopy technique. Based on the results obtained from the XAS and NMR techniques, it was found that the increasing the titanium concentration does not affect significantly the short-range order around Ti, Ba and B atoms. An analysis of the SHG data obtained from the crystallized surface of the glassy samples indicated that the SHG coefficient, def, was comparable to that of the z-quartz monocrystalline sample and, in the sample containing 16 mol% of TiO2, it corresponded to 70% of the value observed for the monocrystalline beta-BBO sample

La formulation des lubrifiants utilisés dans l'automobile est complexe du fait du nombre important d'additifs mélangés aux huiles de base. Pour orienter le choix des formulateurs, il est non seulement nécessaire de connaître le mécanisme d'action de chaque additif mais aussi les interactions entre ces additifs. Pour mieux appréhender ces mécanismes, une démarche originale a été mise en place dans cette étude. Celle-ci consiste à simuler expérimentalement la lubrification en régime limite par la lubrification en phase gazeuse. Pour cela, des molécules de faible poids moléculaire modélisant les différents constituants d'un lubrifiant ont été introduites sous ultravide. Ce type d'expérience a pu être réalisé grâce au développement d'un nouveau Tribomètre à Environnement Contrôlé (TEC) connecté à un système d'analyse de surface. Cette technique permet de simplifier le système tribologique et d'étudier in situ les tribofilms formés en phase gazeuse par des analyses de surface (XPS/AES). Différentes molécules ont été étudiées : triméthylborate (TMB), triméthylphosphite (TMPi) et triméthylphosphate (TMPa) modélisant respectivement les additifs boratés et phosphorés des lubrifiants de transmission. Cette simulation expérimentale a pu être validée en comparant les résultats en phase gazeuse avec ceux obtenus en phase liquide. Des observations en microscopie optique et des analyses chimiques ont mis en évidence la formation de tribofilms. Les expériences réalisées en présence de TMB ont permis de confirmer les résultats de la littérature sur la formation d'un tribofilm non sacrificiel de borates de type « minéral ». Les expériences réalisées avec les molécules phosphorées ont permis de montrer la différence entre les phosphates et les phosphites, notamment la formation d'un composé de type phosphure de fer en présence de TMPi. Les analyses in situ sur les tribofilms obtenus en présence de TMPi ont permis de déterminer le mécanisme de formation du composé phosphure de fer. La réalisation de mélanges de gaz a permis également de mettre en avant les effets de synergie et d'antagonisme entre les additifs

The synthesis and reactions of hydrotris(pyrazolyl)borate, (TpR,R) supported ytterbium(II) borohydride and lanthanide(III) dialkyl (Ln = Yb, Lu) complexes were investigated. The lanthanide(III) dialkyl complexes were found to undergo both hydrogenolysis reaction and protonolysis reaction with terminal alkynes. Reaction of [(TptBu,Me)YbH]2 (1) with NH3BH3 and (TptBu,Me)YbI(THF) (2) with NaBH4 afforded the corresponding mono-ligand complexes, (TptBu,Me)Yb(BH4) (3) and (TptBu,Me)Yb(BH4)(THF) (4), respectively. Compounds 3 and 4 represent rare examples of lanthanide(II) tetrahydroborate complexes. IR spectroscopy data, in the B-H stretching region are consistent with the 3-BH4 bonding mode found in the solid state of compound 4 and the corresponding deuterium labelled BD4 analogue of 4 shows the expected IR isotope shifts. Mono-ligand lanthanide dialkyl complexes, (TpR,R)Ln(CH2SiMe2R)2(THF)0/1 (5-9) were synthesized from the homoleptic Ln(CH2SiMe2R)3(THF)2 (Ln = Yb, Lu; R = Me, Ph) complexes by two alternative and complementary methods: alkyl abstraction with the thallium salts of the ligands, TlTpR,R and protonolysis using the acid form of the ligands, HTpR,R. Hydrogenolysis of the dialkyl complexes (TpMe2)Ln(CH2SiMe3)2(THF) (7a, Yb; 8a, Lu) afforded the corresponding tetranuclear hydride complexes, [(TpMe2)LnH2]4 (11, Yb; 12, Lu). Similarly, hydrogenolysis of (Tp)Yb(CH2SiMe3)2(THF) (9) afforded the hexanuclear hydride [(Tp)YbH2]6 (13). When treated with a variety of terminal alkynes, the dialkyl complexes, (TpR,Me)Ln(CH2SiMe3)2(THF) (14a, Y; 8a, Lu), gave the corresponding bis-alkynide complexes, (TpR,Me)Ln(CCR)2 (15-27). The structures of the complexes depend on the steric size of both the alkyne substituents and the substituent on position 3 of the pyrazolyl ring. Except for the bulkiest substituents, the compounds are dimeric with two asymmetric 2-alkynide bridging groups and a coupled alkynide unit bridging the two lanthanide centers via an unusual enyne bonding motif. The synthesis of Lu(CH2Ph-4-R)3(THF)3 (R = H, 28a; R = Me, 28b) was achieved by salt metathesis reactions between KCH2Ph-4-R and LuCl3. Variable temperature NMR studies in THF shows that the formation of these complexes is accompanied by a small amount of the anionic ate K[Lu(CH2PH-4-R)4(THF)n] (30) complexes, which can be prepared independently by reaction of pure Lu(CH2Ph-4-R)3(THF)3 with one equiv. of KCH2Ph-4-R. One of the coordinated THF of 28a could be removed by trituration with toluene to give Lu(CH2Ph-4-R)3(THF)2 (29a). Protonolysis reaction with HTpR,R afforded the corresponding dibenzyl complexes, (TpR,R)Ln(CH2Ph-4-R)2(THF)n (31-33). X-ray crystal structures of complex 4, the dialkyl complexes 5b, 6b, 7 and 8; dihydride complexes 11, 12 and 13; bis-alkynide complexes 15, 16, 17, 21, 22 and 24 as well as the tribenzyl compounds 28a and 29a and dibenzyl complexes 31-33 were determined. The solution behaviour, solid state structures and structural diversity of these complexes are discussed.

In der vorliegenden Arbeit wird die Einkristallzüchtung nach dem Czochralskiverfahren von GdCa4O(BO3)3 (GdCOB) beschrieben. Aus insgesamt 18 Zuchtversuchen, bei denen auch die Ziehgeschwindigkeit zwischen 1 und 3mm/h variiert wurde, wurden erfolgreich nahezu perfekte Einkristalle gewonnen. In einigen Kristallen traten jedoch auch Risse oder Einschlüsse auf. Diese enthielten neben Iridium vom Tiegelmaterial auch andere Phasen des Gd2O3–B2O3–CaO-Systems, sowie P und Yb, deren Herkunft unklar ist. Als Hauptziehrichtung wurde die kristallographische b-Achse gewählt, ergänzt durch einige Experimente in der c-Richtung. In den drei kristallographischen Hauptrichtungen wurden die thermischen Ausdehnungskoeffizienten von GdCOB bestimmt. Diese können in zwei nahezu lineare Bereiche unterteilt werden: von Zimmertemperatur bis etwa 850° C und von 850 bis 1200° C, wobei die Koeffizienten im Hochtemperaturbereich deutlich höher sind (unter 850° C: alpha_a=11.1, alpha_b=8.6, alpha_c=13.3 10^-6/K, oberhalb 850° C: alpha_a=14.1, alpha_b=11.7, alpha_c=17.8 10^-6/K). Daraus ergibt sich, dass ein Phasenübergang höherer Ordnung vorliegen muss. Als mögliche Ursache wurde mittels HT-Raman Spektroskopie ein Ordnungs-Unordnungs-Übergang identifiziert, während dessen die BO3-Gruppen in der Struktur leicht rotieren. Weitere Untersuchungen mittels thermodynamischer Methoden führten zu schwachen, aber eindeutigen Signalen, die diesem Effekt ebenfalls zuzuordnen sind. Obwohl das Material ein vielversprechender Kandidat für piezoelektrische Anwendungen im Hochtemperaturbereich ist, wurde dieser Effekt bisher unzureichend beschrieben. Dieses Verhalten, kombiniert mit den anisotropen thermischen Ausdehnungskoeffizienten, könnte eine der Ursachen für das Vorkommen von Rissen in den Kristallen während der Synthese darstellen. Spektroskopische Untersuchungen ergaben einen großen Transparenzbereich von 340 bis 2500nm (29 400–4000 cm^-1), was für optische Anwendungen von großer Bedeutung ist. / In a series of 18 growth experiments, GdCa4O(BO3)3 (GdCOB) single crystals were successfully grown by the Czochralski method. They have a well-ordered structure, as revealed by single crystal structure analysis. Although the main growth direction was along the crystallographic b-axis, some experiments were conducted using the cdirection. Pulling velocities were varied between 1 and 3mm/h. Except for a few crystals with cracks or elongated "silk-like" inclusions consisting of multiphase impurities, most of the obtained crystals are of good quality. Those inclusions contain iridium, deriving from the crucible, P and Yb with unclear source, and other phases from the system Gd2O3–B2O3–CaO. Thermal expansion coefficients of GdCOB were determined in the directions of the crystallographic axes and found to be approximately linear in two temperature ranges: from 25° C to around 850° C, and from 850 to 1200° C, with the latter range showing significantly higher coefficients (below 850° C: alpha_a=11.1, alpha_b=8.6, alpha_c=13.3 10^-6/K, and above 850° C: alpha_a=14.1, alpha_b=11.7, alpha_c=17.8 x10^-6/K). This sudden increase of thermal expansion coefficients indicates a phase transition of higher order. An order-disorder transition in form of the rotation of BO3-triangles in the structure was made tentatively responsible for this transition, as revealed by HT-Raman spectroscopy. This transition was also detected by DSC-methods but appeared to result in very weak effects. Although the material is thought to represent a promising candidate for high temperature piezoelectric applications (noncentrosymmetric space group Cm), this effect of change in specification has not been described and it is unknown whether it has influence on the piezoelectric properties. Furthermore, this characteristic behaviour in combination with anisotropic coefficients may be the reason for the development of cracks during cooling of crystals, making the growth difficult. Spectroscopic investigation revealed a wide transparency range from 340 to 2500nm (29 400–4000 cm^-1) of GdCOB, which is a very important property for optical applications.

Present day advanced technologies heavily rely on one particular class of matter, i.e. the crystals. It is the periodic nature of the atoms and the properties arising due to the periodicity in crystals that is exploited to meet various technological feats. The technological revolutions in the semiconductor, optics and communication industries are the examples. The anisotropy in the crystals gives them enhanced properties as required in the field of non-linear optics. The field of non-linear optics became practically a reality after the invention of lasers. The coherent and monochromatic optical beams in the visible and ultraviolet ranges are in high demand due to their application in the fields like material processing, semiconductor lithography, laser micromachining, laser spectroscopy, photochemical synthesis, inertial confinement fusion and other basic scientific studies. In this thesis, work on the growth and characterization of two technologically important non-linear optical crystals has been carried out after developing the necessary instrumentation and some novel techniques for synthesis and growth. Also, studies on the glassy nature of one of the crystals have been carried out. This thesis consists of seven chapters. The first chapter gives a brief introduction to the nonlinear optical phenomenon, crystal growth and glassy state. Instrumentation is the backbone of crystal research technology. Without precision growth equipments large size crystals cannot be grown and without precision characterization instrumentation no conclusion regarding the quality and usefulness of the grown material can be drawn. The work reported in Chapter 2 describes the instrumentation developed for the growth, processing and characterization of crystals grown by solution and melt growth techniques. In low temperature solution growth, crystal growth workstations have been developed using tanks (made of acrylic), heating elements, and stirring propellers. Cooling coils have been inserted into the designed water bath to grow crystals below ambient also. This bath has an advantage to work over a wide range of temperatures, so that maximum retrieval of the material is possible. The growth of large crystals is usually hindered due to spurious nucleation precipitating during the growth process. A novel nucleation-trap crystallizer has been designed and developed that facilitates the continuation of the growth run in spite of extra nucleation precipitating after seeding. In this crystallizer, the spurious nuclei and any other particles generated after the filtration are forced into a well, and the growth of spurious nuclei is arrested by manipulating the temperature of this trap. Achieving adequate heat flow and mass flow profiles is of vital importance for growing good quality crystals. An optimized stirring procedure for the solution or melt is needed for ensuring the desired supply of growth units to the crystal-nutrient interface, and for transporting away any debris of the crystal-growth process. An ACRT set up has been designed and developed. For the growth of crystals by the flux technique and from direct melt, a crystal puller has been designed and developed. The crystal puller consists of a crystal rotation unit, slow and fast pulling mechanisms and a control unit. The pulling assembly is protected from damage caused by possible human errors through interlock mechanisms. The vibration at the shaft of the seed rotation assembly has been minimized by using a dc motor for rotation. A versatile triangular / square wave oscillator has been designed for developing a dc motor control. By implementing this control, the speed of the motor does not vary with supply-voltage variations. A quarter-step switching logic sequence is introduced for stepper motors, which is used for the slow UP/DOWN movement of the puller. This puller can be controlled locally by a control panel provided with the puller, or through a PC remotely by bypassing the local control. Additionally, for the processing and characterization of the grown DKDP crystals, a closed-loop thread-cutter, a ferroelectric loop tracer, and a computer-controlled system for measuring the half-wave voltage have been developed. A novel mercury encapsulant seeding technique that facilitates the processing of solution with immersed seed is invented and has been described in Chapter 3. This technique allows processing of solution with the seed inside the growth chamber, and still avoids contamination of the solution and formation of crystal clusters that are normally generated when seed is inserted after processing of the solution. DKDP and KAP crystal seeds have been used to check the dissolution of seeds, if any, when immersed in pure water for several hours and at high temperatures after introducing the seal. It has been observed that the mercury seal does not allow creeping of water into the seed holder, and there is no dissolution of the seed. This technique has been practically implemented for the growth of crystals from aqueous solution and its usefulness has been demonstrated by growing ammonium acid phthalate, potassium acid phthalate and potassium di-deuterium phosphate crystals. Nonlinear-optical crystals find major use in inertial-confinement fusion (ICF) experiments. For such applications, nonlinear crystals with very large damage-resistance are needed. Alternatively, crystals with moderate damage resistance but large size can be used for frequency-conversion for efficient plasma experiments. Potassium di-hydrogen phosphate, KH2PO4 (KDP) and its deuterated analog, K(DxH1-x)2PO4 (DKDP) are at present the only nonlinear optical crystals which can be grown to large sizes and are suitable for ICF studies. Also, solid-state light valves, light deflectors, and laser communication devices require large and perfect tetragonal DKDP crystals, with high deuterium concentration for easier operation. Chapter 4 describes the growth and characterization of DKDP crystals. DKDP crystals have been grown by all the three techniques i.e. conventional, platform and novel mercury encapsulant seeding techniques. Details about a new approach for the synthesis of DKDP solution have been given. A comparative study of the grown crystals by mercury-encapsulant technique and other techniques is described. Habit modification was observed due to the placement of seed crystals at an off-centre position and orientation in mercury encapsulant seeding technique and has been discussed. The grown crystals have been characterized for homogeneity, dislocations, transmission, DSC, rockng curve, etc. Due to the higher photon energies and the ability to be more tightly focused, coherent radiations of shorter wavelength (deep-UV) are in demand. The photon energies in this region are sufficient for bond-breaking processes in many materials, and find applications in fields like material processing, semiconductor lithography, laser micromachining, laser spectroscopy, photochemical synthesis, etc. Although excimer lasers (XeCl, KrF, ArF etc.) produce significant power in the deep-UV region, these laser systems involve corrosive gases, and are bulky, apart from requiring regular maintenance. A maintenance-free, compact, solid-state laser is preferable. But this, in turn, requires an efficient NLO crystal in that region. CLBO is one such crystal. Growth of CLBO crystals has been carried out by the flux-growth technique using B2O3-deficient flux, as well as from stoichiometric melt and has been discussed in Chapter 5. It was observed that the nucleation of material on platinum wire or spontaneous nucleation was difficult to achieve in spite of high supercooling. After forcing cracks into the mass deposited on platinum wire nucleation could be achieved. The growth of crystals was carried out on seeds with different orientations. Transmission studies, etch-pit studies and harmonic-generation experiments were performed on the grown crystals. The glass-forming tendency of CLBO has been studied and reported in Chapter 6. DTA experiments show that CLBO melt generally transforms to glass on cooling. Even at a cooling rate as low as 1°C/min, the material does not crystallize but transforms into glass. Ergodicity making and glass transition temperatures were determined for glassy CLBO. Since neither the crystallization peak nor the melting peak was observed in DTA experiments during the heating part of thermal cycle for glassy CLBO, a new approach of seeded crystallization was adopted in the calorimetric experiments to achieve crystallization. Since the size of added nuclei is already above the critical radius, the onset of crystallization peaks is independent of the critical-radius energy barrier. Kissenger method was applied to determine the activation energy of seeded- crystallization process. The transformation of glass CLBO to the crystalline phase is mediated by dendrites. Possibility of bulk crystal growth from the glassy state has been discussed, and a novel idea of surface crystallization is proposed. Chapter 7 summarizes the work carried out and projects the scope for future work.