Polykristallines Sr3Gd2[BO3]4 (SGB) konnte mithilfe einer stöchiometrischen Mischung aus SrCO3, Gd2O3 und B2O3 durch zweimaliges Sintern bis 1.350 °C phasenrein erzeugt werden. Ein Exzess von 3 Ma% B2O3 musste der Mischung beigesetzt werden, um das an B2O3 gebundene Wasser auszugleichen [125]. Kristalle des SGB ließen sich mit verschiedenen Orientierungen erfolgreich mit dem Czochralski-Verfaren synthetisieren. Unter Einsatz eines arteigenen, b-orientierten Keimes, einer Translation von 1 mm/h und einer Rotation von 4 /min konnten Kristalle mit guter Qualität bei hoher Erfolgsrate produziert werden. Bei den gezüchteten Kristallen waren keine Segregationserscheinungen zwischen Gadolinium und Strontium feststellbar. Jedoch weist das Auftreten von Fremdphasen (vor allem Gd2O3) in wenigen Kristallen auf eine mögliche, geringfügige Bevorzugung des Sr in der Struktur hin. Die Härte des Materials ist mit ca. 5,5 nach Mohs bestimmt, die Dichte mit 5,15(1) g/cm3. SGB ist nicht hygroskopisch, lässt sich aber in mineralischen Säuren lösen. Die Schmelztemperatur konnte mit 1.461+/-5 °C bestimmt werden. Einkristallines SGB besitzt ein Transmissionsfenster zwischen 215-3.450 nm. Das entspricht einer Bandlücke von 5,4 eV. In diesem Bereich werden über 80% des eingestrahlten Lichtes transmittiert. Im ultravioletten Spektrum finden sich für Gd charakteristische Absorptionsbanden, die durch Elektronenübergänge erzeugt werden. Im mittleren Infrarotbereich lassen sich um die Absorptionskante mehrere Absorptionsbanden, deren Ursache ungeklärt ist, feststellen. Sie stehen offensichtlich im Zusammenhang mit dem Auftreten von [BO3]3- -Gruppen, da sie auch bei anderen Boraten, wie dem Ca4Gd[O|(BO3)3] [99], vorkommen. Gepulvertes SGB weist im Bereich von 550-1.600 cm-1 zahlreiche Absorptionsbanden, die auf verschiedene Schwingungen innerhalb der [BO3]3- -Gruppe zurückgeführt werden können, auf. Es folgen zu kleineren Wellenzahlen hin vermutlich Sr-O- und Gd-O-Schwingungen. Die thermische Ausdehnung von SGB-Kristallen ist anisotrop sowohl zwischen den kristallographischen Richtungen a, b und c als auch über die Temperatur innerhalb einer Richtung. Sie kann im Mittel zwischen 150-830 °C mit alpha11=18,1(2)*10-6/K, alpha22=8,9(3)*10-6/K und alpha33=20,3(4)*10-6/K angenommen werden. Die Ausdehnungskurven deuten mehrere Effekte an, wobei ein Effekt im Bereich von 450-700 °C und vermutlich zwei weitere im Bereich von 800-1.000 °C zu beobachten sind. Aufgrund der Stetigkeit der Kurve ist wahrscheinlich von Phasenübergängen höherer Ordnung auszugehen. Zur Struktur des SGB konnten wichtige Grundverständnisse gewonnen werden. So lässt sich die Struktur bei Raumtemperatur nicht durch eine orthorhombisch zentrische Metrik beschreiben, da die Einzelreflexe bei Einkristallmessungen eine Aufspaltung im Bereich von 0,1 ° zeigen. Dies deutet auf das Vorhandensein von Zwillingen und auch auf eine mögliche monokline Metrik hin. Es fällt dabei besonders auf, dass die Aufspaltung mit zunehmendem Theta-Winkel nicht größer wird, so dass auch andere Phänomene für die Reflexaufspaltung verantwortlich sein könnten. Dennoch ergeben die ermittelte Raumgruppe Pnam, die zugehörigen Gitterparameter (a0=0,7408 nm, b0=0,8757 nm, c0=1,6057 nm) und Atomkoordinaten ein vereinfachtes Modell zur Veranschaulichung der Struktur. Hoch- und Raumtemperaturstruktur sind bis 700 °C unter Annahme des vereinfachten Modells isomorph, wobei die Gitterparameter entsprechend der Ausdehnung vergrößert sind. Die Gd- und Sr-Positionen sind untereinander mischbesetzt. Außerdem deutet sich eine Positionsfehlordnung einer Sauerstoff-Position an, der Ligand eines Borions auf spezieller Lage ist. Hinweise auf die korrekte Struktur liefern die entdeckten Phasenübergänge und Hochtemperatur-Einkristalldaten. Der in der Dilatometrie entdeckte Effekt zwischen 450-700 °C korreliert mit dem Rückgang der Reflexaufspaltung, die bei ca. 700 °C nicht mehr sichtbar ist, wobei sich dieser Rückgang vermutlich von Raumtemperatur bis 700 °C erstreckt. Damit bestätigt sich, dass der erst genannte Effekt als Phasenübergang höherer Ordnung aufgefasst werden kann. Die festgestellte Positionsfehlordnung von Sauerstoff verringert sich mit steigender Temperatur. Die Mischbesetzung ändert sich ebenfalls bis ca. 500 °C. Beide Effekte sowie auch größeren Schwingungsellipsoide der Sauerstopositionen um die allgemeine Borlage sind vermutlich Ausdruck für den stattfindenden Phasenübergang und verstärken die Annahme einer Zwillingsbildung.

Τα ετερομεταλλικά σύμπλοκα μεταβατικών μετάλλων-λανθανιδίων (Ln) έχουν μεγάλη σημασία εξαιτίας των σημαντικών φυσικών (μαγνητικών και οπτικών) ιδιοτήτων τους. Μόνο λίγες πλειάδες NiII/LnIII και πολυμερή ένταξης έχουν αναφερθεί μέχρι σήμερα. Μία γενική προσέγγιση για τη σύνθεση συμπλόκων NiII/LnIII είναι η στρατηγική που βασίζεται στη χρησιμοποίηση «μεταλλικών συμπλόκων ως υποκαταστατών». Αυτή προϋποθέτει μονοπυρηνικά ή ολιγοπυρηνικά σύμπλοκα NiII με μη-ενταγμένα άτομα Ο. Τέτοια σύμπλοκα μπορούν να θεωρηθούν ως «υποκαταστάτες» και να αντιδράσουν περαιτέρω με οξοφιλικά ιόντα LnIII. Στην παρούσα εργασία έχουμε συνθέσει μία σειρά από νικελιοϋποκαταστάτες βασισμένους στις 2-πυρίδυλο οξίμες: 2-πυρίδυλο αλδοξίμη [(py)CHNOH], μέθυλο 2-πυρίδυλο κετονοξίμη [(py)C(Me)NOH] και φαίνυλο 2-πυρίδυλο κετονοξίμη [(py)C(Ph)NOH]. Χρησιμοποιώντας ποικιλία συνθετικών πορειών απομονώσαμε τα παρακάτω σύμπλοκα: [Ni{(py)C(Me)NOH}3](PF6)(NO3) (1), [Ni3(PO3F)2{(py)C(Me)NOH}6](PF6)2 (2), [Ni(NO3)2{(py)C(Me)NOH}2] (3), [Ni(NO2)2{(py)C(Me)NOH}2].MeOH (4.MeOH), [Ni{(py)C(Me)NOH}3][Ni{(py)C(Me)NOH}2{(py)C(Me)NO}](PF6)3.2H2O (5.2H2O), [Ni{(py)C(Ph)NOH}3](ClO4)2.Me2CO.H2O (6.Me2CO.H2O), [Ni(NO2)2{(py)C(Ph)NOH}2].0.5(n-hexane) (7.0.5(n-hexane)), [Ni3{(py)C(Ph)NO}5{(py)C(Ph)NOH}](ClO4) (8), [Ni{(py)C(Ph)NOH}3](NO3)2.Me2CO (9.Me2CO), [Ni{(py)C(Ph)NOH}3](PF6)(NO3) (10), [Ni(SCN)2{(py)C(Ph)NOH}2].2MeOH (11.2MeOH) και [Ni(SCN)2{(py)CHNOH}2] (12). Οι μοριακές και οι κρυσταλλικές δομές των συμπλόκων προσδιορίστηκαν με κρυσταλλογραφία ακτίνων Χ μονοκρυστάλλου. Τα IR φάσματα των συμπλόκων μελετήθηκαν με βάση τις γνωστές δομές και τους τρόπους ένταξης των εμπλεκόμενων υποκαταστατών. Μερικά από τα σύμπλοκα είναι δυνητικοί μεταλλοϋποκαταστάτες. / Heterometallic transition metal-lanthanide (Ln) complexes are of great importance because of their interesting physical (magnetic and optical) properties. Only few NiII/LnIII clusters and coordination polymers have been reported to date. One general approach for the synthesis of NiII/LnIII complexes is the “metal complexes as ligands” strategy. This employs mononuclear or oligonuclear NiII complexes with uncoordinated O-donor groups; such complexes can be considered as “ligands” and further react with the oxophilic LnIII ions. In the present work we have synthesized a series of nickeloligands based on the 2-pyridyl oximes 2-pyridinealdoxime [(py)CHNOH], methyl 2-pyridyl ketone oxime [(py)C(Me)NOH] and phenyl 2-pyridyl ketone oxime [(py)C(Ph)NOH]. Using various synthetic routes we have isolated the complexes: [Ni{(py)C(Me)NOH}3](PF6)(NO3) (1), [Ni3(PO3F)2{(py)C(Me)NOH}6](PF6)2 (2), [Ni(NO3)2{(py)C(Me)NOH}2] (3), [Ni(NO2)2{(py)C(Me)NOH}2].MeOH (4.MeOH), [Ni{(py)C(Me)NOH}3][Ni{(py)C(Me)NOH}2{(py)C(Me)NO}](PF6)3.2H2O (5.2H2O), [Ni{(py)C(Ph)NOH}3](ClO4)2.Me2CO.H2O (6.Me2CO.H2O), [Ni(NO2)2{(py)C(Ph)NOH}2].0.5(n-hexane) (7.0.5(n-hexane)), [Ni3{(py)C(Ph)NO}5{(py)C(Ph)NOH}](ClO4) (8), [Ni{(py)C(Ph)NOH}3](NO3)2.Me2CO (9.Me2CO), [Ni{(py)C(Ph)NOH}3](PF6)(NO3) (10), [Ni(SCN)2{(py)C(Ph)NOH}2].2MeOH (11.2MeOH) and [Ni(SCN)2{(py)CHNOH}2] (12). The molecular and crystal structures of the complexes have been determined by single-crystal X-ray crystallography. The IR spectra of the complexes have been discussed in terms of the known structures and the coordination modes of the ligands involved. Some of the complexes have the potential to act as metalloligands.

Η σύνθεση και ο χαρακτηρισμός πλειάδων των μετάλλων μετάπτωσης σε ενδιάμεσες οξειδωτικές βαθμίδες αποτελεί σήμερα έναν από τους κύριους ερευνητικούς στόχους πολλών επιστημονικών ομάδων παγκοσμίως εξαιτίας των εφαρμογών που βρίσκουν σε διάφορα επιστημονικά πεδία, όπως στη βιοανόργανη χημεία, στην επιστήμη των υλικών, στη μοριακή φυσική και στη θεωρητική χημεία. Οι πλειάδες αυτές περιέχουν πολλές φορές έναν ασυνήθιστα μεγάλο αριθμό ασυζεύκτων ηλεκτρονίων στη θεμελιώδη κατάσταση και παρουσιάζουν εξαιρετικό ενδιαφέρον από μαγνητικής απόψεως. Αυτό συμβαίνει γιατί μια υψηλή τιμή spin στη θεμελιώδη κατάσταση είναι αναγκαία (άλλα όχι ικανή) συνθήκη ώστε αυτού του είδους οι σύμπλοκες ενώσεις να εμφανίζουν το φαινόμενο του μονομοριακού μαγνητισμού (single-molecule magnetism). Στην παρούσα Εργασία μελετήθηκε το σύστημα αντίδρασης μαγγάνιο/α-βενζοΐνη οξίμη (α-benzoin oxime, bzoxH2) κάτω από βασικές συνθήκες, το οποίο οδήγησε στην απομόνωση και το δομικό (μέσω κρυσταλλογραφίας ακτίνων-Χ σε μονοκρυστάλλους) και μαγνητοχημικό χαρακτηρισμό των μοριακών πλειάδων [Mn8O4(bzox)8(MeOH)4] (1), [Mn9O2(bzox)11(bzoxH)(MeOH)4(H2O)2] (2) και [Mn9O2(bzox)11(bzoxH)(H2O)6] (3). Τα σύμπλοκα 1-3 αποτελούν τις πρώτες δομικά χαρακτηρισμένες πλειάδες τρισθενών μεταλλοϊόντων με υποκαταστάτη την α-βενζοΐνη οξίμη. Το σύμπλοκο 1 αποτελείται από οκτώ ιόντα MnIII, με το δομικό του πυρήνα να παρουσιάζει μία πρωτότυπη τοπολογική διευθέτηση τεσσάρων τριγωνικών Mn3 υπομονάδων, ανά δύο κάθετων μεταξύ τους, η οποία οδηγεί σε μια ενδιάμεση τιμή spin στη θεμελιώδη κατάσταση, SΤ = 2. Τα ισοδομικά σύμπλοκα 2 και 3 αποτελούνται από εννέα ιόντα MnIII, με το δομικό τους πυρήνα να παρουσιάζει μία επίσης πρωτότυπη τοπολογική διευθέτηση εναλλασσσόμενων τριγωνικών και γραμμικών Mn3 υπομονάδων, η οποία οδηγεί σε μια ενδιάμεση τιμή spin στη θεμελιώδη κατάσταση, SΤ = 3. / The synthesis and characterization of polynuclear metal complexes (clusters) containing paramagnetic 3d-metal ions in intermediate oxidation states have gained intense interest due to the applications of these compounds in several fields of science, such as bioinorganic chemistry, materials science, molecular physics and theoretical chemistry. Such high nuclearity transition metal clusters are one of the growing research subjects in Molecular Magnetism, given the fact that they often possess a fairly large ground-state spin value, which is one of the necessary requirements for a molecule to be able to exhibit the phenomenon of single-molecule magnetism. In the present work, we studied the reaction scheme manganese/α-benzoin oxime (bzoxH2) under basic conditions, which has led to the isolation, and structural (through single-crystal X-ray crystallography) and magnetochemical characterization of the molecular complexes [Mn8O4(bzox)8(MeOH)4] (1), [Mn9O2(bzox)11(bzoxH)(MeOH)4(H2O)2] (2) and [Mn9O2(bzox)11(bzoxH)(H2O)6] (3). Complexes 1-3 are the first structurally characterized trivalent metal clusters with the ligand α-benzoin oxime. Compound 1 consists of eight MnIII atoms and its irregular metal core presents an unprecedented topology based on four triangular Mn3 units, which are vertical to each other, thus leading to an ST = 2 ground state. The isostructural compounds 2 and 3 comprise nine MnIII atoms arranged in a unusual topology based on linear and triangular Mn3 units, thus leading to an ST = 3 ground state.

Η σύνθεση και ο χαρακτηρισμός πλειάδων των μετάλλων μετάπτωσης σε ενδιάμεσες οξειδωτικές βαθμίδες αποτελεί σήμερα έναν από τους κύριους ερευνητικούς στόχους πολλών επιστημονικών ομάδων παγκοσμίως εξαιτίας των εφαρμογών που βρίσκουν σε διάφορα επιστημονικά πεδία, όπως στη βιοανόργανη χημεία, στην επιστήμη των υλικών, στη μοριακή φυσική και ηλεκτρονική, και στη θεωρητική χημεία. Οι πλειάδες αυτές περιέχουν πολλές φορές έναν ασυνήθιστα μεγάλο αριθμό ασυζεύκτων ηλεκτρονίων στη θεμελιώδη κατάσταση και παρουσιάζουν εξαιρετικό ενδιαφέρον από μαγνητικής απόψεως. Αυτό συμβαίνει γιατί μια υψηλή τιμή spin στη θεμελιώδη κατάσταση είναι αναγκαία (άλλα όχι ικανή) συνθήκη ώστε αυτού του είδους οι σύμπλοκες ενώσεις να εμφανίζουν το φαινόμενο του μονομοριακού μαγνητισμού (single-molecule magnetism). Στην παρούσα Εργασία μελετήθηκε το σύστημα αντίδρασης μαγγάνιο/2-πυριδυλομεθανόλη (hmpH), παρουσία ή απουσία κυανικών ιόντων (OCN-) και κάτω από βασικές συνθήκες, το οποίο οδήγησε στην απομόνωση και το δομικό (μέσω κρυσταλλογραφίας ακτίνων-Χ σε μονοκρυστάλλους) και μαγνητοχημικό χαρακτηρισμό των πλειάδων [Mn7(OH)3(OCN)3(hmp)9](ClO4)2 (1), [Mn16O8(OMe)4(OCN)4(O2CMe)12(hmp)6(MeOH)2] (2), [Mn18O14(O2CMe)18(hmp)4(hmpH)2(H2O)2] (3) και [Mn18O14(O2CEt)18(hmp)4(hmpH)2(H2O)2] (4). Οι πλειάδες 1-4 είναι μικτού-σθένους (ΙΙ/ΙΙΙ). Το σύμπλοκο 1 αποτελεί ένα νέο μέλος μιας μεγάλης οικογένειας επταπυρηνικών συμπλόκων με το δομικό πυρήνα τους να περιλαμβάνει έξι ιόντα Mn διευθετημένα κυκλικά γύρω από ένα έβδομο κεντρικό ιόν Mn2+. Τα σύμπλοκα 2, 3 και 4 αποτελούν παραδείγματα υψηλής πυρηνικότητας και συμμετρίας πλειάδων του Mn, με αισθητικά όμορφες δομές και ενδιαφέρουσες μαγνητικές ιδιότητες. / The synthesis and characterization of polynuclear metal complexes (clusters) containing paramagnetic 3d-metal ions in intermediate oxidation states have gained intense interest due to the applications of these compounds in several fields of science, such as bioinorganic chemistry, materials science, molecular physics and electronics, and theoretical chemistry. Such high nuclearity transition metal clusters are one of the growing research subjects in Molecular Magnetism, given the fact that they often possess a fairly large ground-state spin value, which is one of the necessary requirements for a molecule to be able to exhibit the phenomenon of single-molecule magnetism. In the present work, we studied the general reaction system manganese/2-(hydroxymethyl)pyridine (hmpH), in the presence or absence of cyanate ions (OCN-), under basic conditions, which has led to the isolation, and structural (through single-crystal X-ray crystallography) and magnetochemical characterization of the compounds [Mn7(OH)3(OCN)3(hmp)9](ClO4)2 (1), [Mn16O8(OMe)4(OCN)4(O2CMe)12(hmp)6(MeOH)2] (2), [Mn18O14(O2CMe)18(hmp)4(hmpH)2(H2O)2] (3) and [Mn18O14(O2CEt)18(hmp)4(hmpH)2(H2O)2] (4). All complexes 1-4 are mixed-valent (II/III). Complex 1 is a new member of a growing family of heptanuclear clusters with a core consisting of six Mn ions arranged in a ring around a seventh central Mn2+ ion. Complexes 2, 3 and 4 are examples of high-nuclearity and high-symmetry Mn clusters with aesthetically pleasing structures and interesting magnetic properties.

No description available.

Le grenaillage est souvent utilisé sur les pieds d’aube de turbine haute pression afin de retarder l’apparition des fissures dans les zones de concentration de contraintes. Ce traitement de surface génère des contraintes résiduelles et de l’écrouissage en surface de la pièce, ce qui influe sur sa durée de vie. L’enjeu de cette thèse est de mettre en place une méthodologie permettant de prendre en compte cet état mécanique initial, ainsi que son évolution en service, dans l’analyse de durée de vie d’une aube élaborée en superalliage monocristallin à base de nickel (AM1). Tout d’abord, cet état mécanique (contraintes résiduelles et écrouissage) est déterminé expérimentalement. Les contraintes résiduelles sont notamment évaluées par diffraction des rayons X en utilisant la méthode d’Ortner. Cet état mécanique est ensuite introduit dans les calculs de structure. Pour cela, on s’inspire de la méthode connue de l’introduction directe du champ d’eigenstrains qui est, ensuite, étendue afin d’introduire également les variables d’écrouissage ainsi que l’état mécanique anisotrope complet dans toute la structure. L’étape suivante a visé à suivre expérimentalement et à modéliser l’évolution de ces quantités sous sollicitations thermique, d’une part et cycliques à température constante (650°C), d’autre part. Enfin, la chaîne complète de calcul de durée de vie de l’AM1 est appliquée afin d’analyser la durée de vie des éprouvettes grenaillées. Les résultats obtenus sont discutés en regard des essais de fatigue effectués sur éprouvettes représentatives / Shot-peening is widely used on roots of high pressure turbine blade to postpone crack initiation in stress concentration area. This pre-stressing introduces compressive residual stress and strain hardening in a surface layer which will influence lifetime. The aim of this thesis is to propose a methodology which allows taking into account the impact of such pre-stressing and their evolution on the fatigue behaviour of a single crystal nickel-based superalloy (AM1) used for high pressure turbine blades. Firstly, the experimental work is devoted to the determination of the initial mechanical state (residual stresses and strain hardening). Residual stresses are namely determined using X-ray diffraction involving the use of a specific method developed by Ortner. This experimental initial mechanical state is then introduced as an input in structure calculation. The well-known method involving the direct introduction of eigenstrain profiles is used and improved to also introduce strain hardening variables and the complete anisotropic mechanical state in all the integration points of the structure. The next step consist in following experimentally and modeling the evolution of these quantities under thermal and mechanical loads under an uniform temperature (650°C). Finally, the complete lifetime assessment is carried out on representative shot-peened samples. Results are discussed with respect to experimental fatigue tests

Fe chalcogenides : The discovery of superconductivity in Fe based compounds trig- gered an intense research activity in this field with significant importance given to material synthesis. As a result, numerous materials falling into four major classes and sharing similarities in physical properties were synthesized and investigated. In spite of subtle differences, all of them share many common features like crystal symmetry, magnetic ground state, close resemblance in phase diagram etc. Fe super- conductors are broadly classified into Fe pnictides (with Fe − pnictogen layer) and Fe chalcogenides (with Fe − chalcogen layer) in which the binary Fe chalcogenides possess the simplest crystal structure. The distinct magnetic and superconducting properties make them interesting candidates for research. Detailed study on such systems demand high quality single crystals. This thesis discusses single crystal growth and properties of Fe1+yTe1−xSex. Struc- tural, magnetic, superconducting and thermal properties of pristine and substituted compounds are explored. A characteristic feature associated with binary chalco- genides is the presence of excess Fe in the interstitial sites represented by y in the chemical formula. By fine tuning the composition, the effect of interstitial Fe on various physical properties can be analyzed. The current work deals with the influence of interstitial excess Fe on the structural, magnetic and superconducting properties of the parent compound Fe1+yTe and Se substituted Fe1+yTe1−xSex. The results are organized into eight chapters; an outline of each chapter is given below. Chapter 1 gives an introduction to the broad field of Fe superconductors. A de- tailed literature review providing comparison of Fe pnictides with chalcogenides is included. The background of the current work is discussed with reference to the im- portant aspects of crystal structure and its relation to the ordered ground states. An overview of the important theories on magnetic ordering and superconducting pair- ing is provided. In the later part, a generic phase diagram along with the individual phase diagrams of important systems are discussed. This is followed by a discus- sion of the characteristic properties of iron chalcogenides and different methods of bulk synthesis. The chapter is concluded with a note on the motivation behind the present work. Chapter 2 discusses the crystal growth techniques and experimental methods used in the present work. The basic working principles are briefly explained. Chapter 3 provides a detailed discussion of the single crystal growth procedure, its customization and basic characterization. Single crystals of all compositions un- der discussion are grown by a modified horizontal Bridgman method. Material preparation, growth parameters and overall temperature profile of crystal growth process are described. Single crystalline nature of the as-grown crystals is con- firmed with Laue scattering technique. All crystals show tetragonal symmetry at room temperature. The approximate crystal orientation is deduced by indexing the X-ray diffraction pattern of the cleaved crystals. The diffraction patterns exhibit a set of (00l) peaks. A detailed composition analysis is performed on the samples. The sample properties are very sensitive to composition and careful estimation is per- formed by conducting repeated measurements at multiple points on the samples under study. Chapter 4 deals with superconducting and magnetic properties of Fe1+yTe0.5Se0.5. Single crystals of two different Fe concentration, y=0.04 and 0.09 are grown in which the concentration of Se and Te are maintained close to 0.5. Among binary Fe chalcogenides, half substituted iron telluride shows the highest TC (15 K) at ambient pressure. Accordingly, this composition is chosen to evaluate the role of Fe concentration in modulating the superconducting behavior. Two different batches of both the samples are grown, one set containing small amounts of impurity phases and the other, representing a pure primary phase. Resistivity measurements performed on both compositions, y=0.04 and 0.09, show onset of superconductivity near 15 K. In the normal state above TC, the temperature derivative of resistivity dρ/dT changes from positive to negative as the excess Fe concentration rises. At higher Fe concentrations, a log 1/T divergence is discernible in the normal state. The contribution of interstitial Fe to superconductivity has been analyzed using magnetization measurement techniques. An increase in the width of superconducting transition is seen in all measurements as the Fe content increases. The superconducting volume fraction estimated from susceptibility data demonstrates that high concentration of Fe is not favorable to superconductivity. The upper and lower critical field are esti- mated from electric resistivity data (in applied magnetic field) and magnetization isotherms respectively. Comparison of the lower critical field between two compo- sitions strengthens the argument that higher excess Fe leads to suppression of super- conductivity. The second set of crystals with impurity phases reveals an anomalous magnetization peak near 125 K. The results from resistivity, DC magnetization and ac susceptibility are compared. Chapter 5 addresses the influence of excess Fe on the ordered ground state. The antiferromagnetic parent compound, Fe1+yTe single crystals, are also grown using the same procedure. It is proposed that excess Fe occupying the interstitial sites possess local moments which could interact with the magnetic phases. In an at- tempt to understand their magnetic properties in detail, single crystals are grown with y=0.06, 0.09, 0.11, 0.12, 0.13 and 0.15. Fe1+yTe undergoes magnetostructural transition at TN=67 K. As the concentration of Fe varies from 0.06 to 0.13, a marked suppression of TN occurs from 67 K to 56 K. Moreover, a single first order transi- tion is seen to split into two at the critical concentration, y=0.12. The derivative plot of magnetization and specific heat data clearly illustrate two well-separated peaks. The two transitions are denoted as TN=57 K and TS=46 K. TN here is identified as a second order transition and TS as a first order transition. The second order transi- tion is evident from the λ-like nature of the peak in the specific heat measurement. The first order transition is associated with a large thermal hysteresis in the heat- ing and cooling cycle. Raw data from the heat capacity calorimeter gives a clear hint towards the first order nature of TS. As the composition of Fe rises further, the multiple transitions subside and disappear. For higher concentration, y=0.15, a sin- gle continuous phase transition is observed. Impurity free, pure phase is noticed in most of the samples as evident in powder X-ray diffraction and bulk magneti- zation measurements. The thermal data of various compositions are analyzed and compared. Electrical resistivity data clearly reveals the shift in phase transition and the presence of multiple transitions. Unlike Fe1+yTe1−xSex, all compositions here display similar behavior above TN, irrespective of the concentration of excess Fe. Chapter 6 devotes special emphasis to the evolution of structural and magnetic properties of the critical composition, Fe1.12Te where multiple transitions are ob- served. The low temperature structure of the crystal is studied in detail using syn- chrotron powder X-ray diffraction. The data in the vicinity of the two transitions, TN and TS are carefully analyzed. The room temperature crystal structure belongs to tetragonal symmetry with P4/nmm space group, where it is paramagnetic. As the sample is cooled to just below TN, a magnetostructural transition occurs from tetragonal to orthorhombic space group Pmmn. Below TN, the XRD pattern of the tetragonal (200) peak splits into (200) and (020) representing an orthorhombic distortion. The second transition is observed at TS where the orthorhombic struc- ture undergoes a monoclinic distortion, to P21/m. Below TS, a mixed phase of or thorhombic and monoclinic structures are present. The powder diffraction studies are supplemented with thermodynamic measurements. From specific heat analy- sis, the different contributions and the change in entropy across the transitions are estimated. Linear thermal expansion study has confirmed the two structural transi- tions. The changes occurring in lattice parameters, bond distances, bond angles and unit cell volume as a function of temperature are calculated using powder pattern refinement. Synchrotron data, linear thermal expansion and thermodynamic mea- surement results all point to strong magnetostructural coupling in this material. A temperature-composition phase diagram is formulated using results obtained from different Fe compositions. Transition temperature is plotted as a function of excess Fe content, highlighting its role in determining the structural and magnetic phases in Fe1+yTe. Chapter 7 deals with the magnetic and superconducting properties of Se substi- tuted Fe1+yTe1−xSex. Single crystals are grown by carefully varying the concen- tration of Se from x=0.02 to 0.25 while keeping the nominal composition of excess Fe more or less same. In this work, focus is given to Fe-rich, selenium substituted compositions. The intention is to explore how Se substitution affects the multiple transitions observed in Fe1.12Te. At 2% Se substitution, the split peaks are evident with a slight shift in temperature. The temperature interval between the two tran- sitions decreases in comparison to the pristine compound. For further increases in Se concentration, instead of two well separated peaks, a weak broad hump is ob- served. For compositions with x >0.10, long range magnetic ordering is suppressed. As x increases above 0.15 the electrical resistivity drops indicating the onset of su- perconductivity. However, in the composition range 0.15 ≤ x ≤ 0.25, neither long range magnetic order nor bulk superconductivity is present. Alternately, weak magnetic transitions above the superconducting transition are visible. The transport and magnetic properties are similar to that observed in Fe1.09Te0.5Se0.5. By tuning the Se composition in Fe-rich samples, the magnetic and structural transitions, originally seen in the parent compound are suppressed. The emergence of superconductivity is also discussed. The last section of the chapter provides the modified phase diagram as a function of Se concentration, combining all compositions discussed in the thesis. This gives a detailed description of Fe chalcogenides in the composition range, x=0 to 0.5 with special emphasis on Fe rich samples. The different regions in the phases diagram describe the peculiar properties of Fe chalcogenides. Chapter 8 concludes the thesis with general conclusions pertaining to various observations made in the different chapters. Prospects for future work are briefly outlined.

Lors de la phase de certification d’un turbomoteur, le motoriste doit démontrer que la perte d’une pale de rotor ne conduit pas au "Knocking-Off", c’est à dire à la rupture en cascade des pales suiveuses. Cette démonstration est faite en général par un essai au banc coûteux car partiellement destructif. Grâce à l’amélioration des moyens de calcul, il devient possible de simuler la réponse transitoire de la structure soumise à ce type de chargement très complexe. En tant que point d’entrée sur la simulation, la connaissance du comportement des matériaux est primordiale. Or, peu d’études sont publiées sur le comportement dynamique des superalliages à base nickel monocristallins et, de surcroît, à des températures élevées de l’ordre de 1000°C. Pour prédire efficacement les conséquences d’impacts sur des pales de turbines, des travaux expérimentaux et numériques ont été réalisés sur un monocristal couramment utilisé par Turbomeca. Des essais de compression dynamique à haute température sur barres de Hopkinson permettent d’estimer le seuil de plasticité et l’écrouissage du matériau en fonction de l’orientation du cristal, de la vitesse de déformation et de la température. Les paramètres d’une loi visco-plastique anisotrope sont identifiés pour modéliser efficacement le comportement macroscopique du MC2 sous des chargements intenses et fortement multi-axiaux. Une campagne d’essais balistiques au banc de Safran Snecma a été réalisée sur des plaques et des pales monocristallines à hautes températures. Afin de prendre en compte la fragmentation des profils dans les calculs de perte de pale, un critère en déformation plastique dépendante du taux de triaxialité des contraintes est calibré puis validé par confrontation aux essais de tirs sur plaques. Des mesures de stéréo-corrélation postmortem et des enregistrements à la caméra rapide permettent de valider les simulations. Une pratique de modélisation de la perte d’une pale avec l’outil LS-Dyna a été établie et appliquée à un cas industriel de perte de pale en service. Enfin, en vue de justifier le découplage temporel entre les dommages primaires, liés aux impacts directs sur les premières pales suiveuses, et secondaires, liés aux effets de l’excentration, une approche de dynamique d’ensemble de ligne d’arbre a été développée puis validée. / During the certification process of a turbo engine, the engine manufacturer has to demonstrate that the loss of a rotor blade does not lead to the "knocking-off" phenomenon, in other words to the cascading failure of the successive blades. Generally, this demonstration is carried out through a costly rig test driving to the partial destruction of the engine. Thanks to the improvement of computational resources, it is now possible to simulate the transient response of the structure subjected to this complex loading. The knowledge of material behavior turns out to be the essential starting point for the simulation. However, only a few studies have been published on the dynamic behavior of nickel-based single crystal superalloys at high temperature reaching 1000°C. With a view to efficiently predicting the consequences of impacts on turbine blades, experimental and numerical works have been conducted on a single crystal frequently used by Turbomeca. High-temperature dynamic compressive tests on Split Hopkinson Pressure Bars (SHPB) have enabled to estimate the material plasticity level and hardening, depending on the crystal orientation, strain rate and temperature. The parameters of a viscoplastic anisotropic law have been identified to effectively model the MC2 macroscopic behavior under highly intense and multiaxial loading. At Safran Snecma Villaroche, ballistic tests have been undertaken on both single crystal plates and blades under high temperatures. In order to consider the fragmentation of profiles in blade-off simulations, a plastic strain criterion depending on stress triaxiality has been calibrated and validated by comparison with the impacts on blades. Post-mortem digital images correlation measurements and high-speed camera recordings have confirmed these simulations. Using LS-Dyna solver, a blade-off modeling strategy has been created and applied to an actual blade-off industrial case. Finally, a rotordynamics approach has been developed and validated with the aim of separately analyzing the primary damage, caused by direct impacts on the first following blades, and the secondary damage due to the effects of unbalance on a flexible rotor.

The past few decades have witnessed an almost exponential increase in interest in the field of metal organic frameworks (MOFs), which can be evidenced from the large number of scientific articles being published routinely in this area. The MOFs are crystalline hybrid materials built via the judicial use of inorganic metal ions and organic linkers, thereby bridging the gap between purely inorganic and organic materials. The structural versatility and the potential tunability of the MOFs imparts unique physicochemical and thermomechanical properties, which have rendered them immensely useful in the branches of chemistry, material science, physics, biology, nanotechnology, medicine as well as environmental engineering. The MOFs have been shown to be promising as materials for gas storage and separation, sensors, ferroelectric and non-linear optical materials, magnetism, catalysis, drug delivery etc and researchers have been devising strategies to utilize the MOFs to tackle a number of global challenges of the twenty-first century. A survey of the literature reveals that the linear organic linkers, 1,4- benzenedicarboxylic acid (BDC) and 4,4’-biphenyldicarboxylic acid (BPDC), have been the organic linkers of choice for the construction of stable, porous and multifunctional MOFs. The aim of this thesis has been to monitor the effect that the presence of a functional group in between the benzene rings of the BPDC would have on the overall structures and the properties of the MOFs. Thus, as part of the investigations, the preparation of the MOF compounds using 4,4’-sulfonyldibenzoic acid (SDBA) and 4,4’- azodibenzoic acid (ABA) have been accomplished. Along with the conventional hydrothermal and solvothermal synthetic techniques, the liquid-liquid biphasic reaction method was also utilized for the synthesis of some of the compounds. The structures of the compounds were ascertained from single crystal X-ray diffraction technique. Proton conductivity studies were performed on Mn based porous MOFs using AC impedance spectroscopy. The ferroelectric behavior in a Co based porous MOF was established using dielectric and polarization vs electric field measurements. The labile nature of the lattice solvent molecules was established utilizing single crystal X-ray diffraction studies and water sorption experiments. In addition, the site selective substitution in a homometallic MOF and the subsequent conversion to a mixed-metal spinel oxide upon thermal decomposition, have also been studied. Chapter 1 of the thesis is a brief overview of the metal organic framework compounds and summarizes the various important structures that have been reported in literature and the interesting properties that they exhibit. In chapter 2, the proton conductivity behavior, solvent mediated single crystal to single crystal (SCSC) and related structural transformations in a family of Mn and Co based porous MOFs with SDBA have been presented. Also presented are the results of the site selective substitution of Mn by Co in a homometallic Mn based MOF and it’s subsequent decomposition to CoMn2O4 spinel oxide nanoparticles. In chapter 3, the syntheses, structures and the magnetic properties of the pentanuclear Mn5 based MOF compounds with SDBA have been presented. The role of the time and the temperature in the formation of the compounds has also been presented. In chapter 4, the dehydration/rehydration mediated switchable room temperature ferroelectric behavior, the single crystal to single crystal solvent exchange studies and selective gas sorption behavior in an anionic Co based MOF with SDBA has been discussed. In chapter 5, the use of the liquid-liquid biphasic synthetic route in the formation of Zn and Cd based MOFs with ABA has been discussed. Structural transformations between the one dimensional Zn based compounds and the heterogeneous catalytic studies using the Cd based compounds have also been presented.

La formation de polymères de coordination poreux et chiraux ainsi que leur utilisation pour des processus énantiosélectifs est actuellement un des domaines de grand intérêt en chimie. La formation de ces matériaux est rendue possible par le biais des concepts développés dans le domaine de la tectonique moléculaire. Les travaux présentés dans cette thèse s’inscriventdirectement dans cette thématique. Les synthèses de tectons organiques chiraux sont présentées. Leur combinaison avec divers centres métalliques, via différentes méthodes de cristallisation, a permis l’obtention de monocristaux qui ont été étudiés par diffraction des rayons X sur monocristal. Dans un premier temps, des polymères de coordination homochiraux, obtenus par l’utilisation de tectons dotés de sites coordinants neutres sont présentés. Des réseaux de type cuboïde présentant des canaux monodimensionnels au sein de leur architecture sont notamment décrits. Par la suite, des édifices mono- et bi-dimensionnels de géométries diverses sont discutés. Pour certains de ces cristaux, des interactions de plus faible énergie que la liaison de coordination permettent la formation de réseaux moléculaires de plus haute dimensionnalité. Enfin, dans une dernière partie, l’utilisation de tectons dotés de sites coordinants chargés est discutée. Des réseaux tridimensionnels homochiraux poreux et robustes sont décrits. Ces derniers sont des candidats de choix pour des procédés énantiosélectifs de séparation. Leur propension à encapsuler des gaz (N2 et CO2) est présentée. / The synthesis and the use of porous chiral coordination polymers for enantioselective processes are of current interest and prime importance in chemistry. These crystalline materials are mainly obtained by combinations of well-designed organic tectons and properly chosen metallic components. This thesis deals with the synthesis of organic chiral building blocks and their combinations with a variety of metallic salts leading to chiral coordination networks. In a first part, the use of tectons bearing neutral coordinating sites is described. Homochiral cuboid architectures displaying monodimensional channels are presented. In the second part, mono- and bi-dimensional networks of various geometries are described. In some cases, within crystals, interactions lower in energy than the coordination bond are observed and are responsible for the formation of molecular networks of higher dimensionality. Finally, the use of organic tectons displaying charged interaction sites is presented. Their combination with metallatectons under thermal treatments affords robust tridimensional homochiralarchitectures displaying cavities. These materials are interesting candidates for enantioselective recognition and separation. Their gas adsorption propensity (N2 and CO2) is briefly discussed.