No description available.

It is known that boron containing compounds exhibit interesting chemical and physical properties. In the past 50 years modern preparative methods have led to an overwhelming number of different structures of novel and often unexpected boron–sulfur and boron–selenium compounds. Among all these new compounds, there was only one which comprises rare earth metal (RE), boron and heavier chalcogen, namely sulfur, the europium thioborate Eu[B2S4] [1]. Selenoborates of rare earth metals are hitherto unknown. On the other hand, rare earth oxoborates represent a well-known class of compounds [2] with a wide range of applications, especially in the field of optical materials. In addition, well-defined boron compounds containing the heavier group 16 elements are fairly difficult to prepare due to the high reactivity of in situ formed boron chalcogenides towards most container materials at elevated temperatures. The chalcogenoborates of the heavier chalcogens are sensitive against oxidation and hydrolysis and therefore have to be handled in an inert environment. Therefore, developing and optimization of preparative routes for the syntheses of pure and crystalline RE thio- and selenoborates was needed. In the course of this study, the application of different preparation routes, such as optimized high-temperature routes (HT), metathesis reactions and high-pressure high-temperature routes (Hp – HT), led to sixteen new rare earth thioborates. Their crystal structures were solved and/or refined from powder and single crystal X-ray diffraction data, while the local structure around rare earth metal was confirmed from the results of the EXAFS analyses. Quantum mechanical calculations were used within this work in order to investigate the arrangement of intrinsic vacancies on the boron sites in the crystal structures of rare earth thioborates. Thermal, magnetic and optical properties of these compounds are also discussed. The rare earth thioborates discovered during this work are the first examples of ternary thioborates containing trivalent cations. These compounds can be divided into two groups of isotypic compounds: the rare earth orthothioborates with general formula REIII[BS3] (RE = La – Nd, Sm, Gd and Tb) [3] and the rare earth thioborate sulfides with general formula REIII¦9B5S21, (RE = Gd – Lu, and Y) [4]. In the crystal structure of RE[BS3] (orthorhombic, space group Pna21, Z = 4), the sulfur atoms form the vertices of corrugated kagome nets, within which every second triangle is occupied by boron and the large hexagons are centered by RE cations. The structural features of the isotypic RE[BS3] phases show great similarities to those of rare earth oxoborates RE[BO3] and orthothioborates of alkali and alkaline earth metals as well as to thallium orthothioborate, yet pronounced differences are also observed: the [BS3]3– groups in the crystal structures of RE[BS3] are more distorted, where the distortion decreases with the decreasing size of the RE element, and the coordination environments of the [BS3]3– groups in the crystal structures of RE[BS3] are different in comparison with the coordination environments of the [BO3]3– groups in the crystal structures of λ-Nd[BO3] [5] and of o-Ce[BO3] [6]. The results of the IR and Raman investigations are in agreement with the presence of [BS3]3– anions in the crystal structure of RE[BS3]. Thermal analyses revealed the thermal stability of these compounds under inert conditions up to ~ 1200 K. Analyses of the magnetic properties of the Sm, Gd and Tb thioborates showed that both Gd and Tb phases order antiferromagnetically. The magnetic susceptibility for Sm orthothioborate approximately follows the Van-Vleck theory for Sm3+. Between 50 K and 62 K a transition appears which is independent of the magnetic field: the magnetic susceptibility becomes lower. This effect might indicate a discontinuous valence transition of Sm which was further investigated by means of XANES and X-ray diffraction using synchrotron radiation, both at low temperatures. The series of isotypic RE thioborate sulfides with composition RE9B5S21, was obtained by the application of Hp – HT conditions to starting mixtures with the initial chemical composition “REB3S6“, after careful optimization of the pressure, temperature and treatment time, as well as the composition of the starting mixtures. Their crystal structures adopt the Ce6Al3.33S14 [7] structure type (hexagonal, space group P63, Z = 2/3). The special features of the RE9B5S21 crystal structures, concerning boron site occupancies and different coordination environments of the two crystallographically independent boron sites, were investigated in more detail by means of quantum chemical calculations, electron diffraction methods, optical and X-ray absorption spectroscopy as well as by 11B NMR spectroscopy. The results obtained from these different experimental and computational methods are in good mutual agreement. The crystal structures of the RE9B5S21 compounds are characterized by two types of anions: tetrahedral [BS4]5– and trigonal planar [BS3]3– as well as [(S2–)3] units. Isolated [BS4]5– tetrahedra (all pointing with one of their apices along the polar [001] direction) represent a unique feature of the crystal structure which is observed for the first time in a thioborate compound. These tetrahedra are stacked along the three-fold rotation axes. Vacancies are located at the trigonal-planar coordinated boron site with preferred ordering –B–B––B–B–– along [001]. No superstructure is observed by means of electron diffraction methods as adjacent columns are shuffled along the c axis, giving rise to a randomly distributed vacancy pattern. Positions of the sulfur atoms within the [(S2–)3] substructure as well as planarity of the [BS3]3– units were investigated in more detail by means of quantum mechanical calculations. Results of the IR and Raman spectroscopy, as well as of the 11B NMR spectroscopy are in agreement with the presence of the boron atoms in two different coordination environments. Thermal analyses showed that compounds RE9B5S21 are stable under inert conditions up to ~ 1200 K. In accordance with the combined results of experimental and computational investigations, the chemical formula of the RE9B5S21 compounds is consistent with RE3[BS3]2[BS4]3S3. A short overview of investigations towards rare earth selenoborates, where in most of the cases only known binary rare earth selenides could be identified, is presented as well in this work. Investigations in the RE–B–Se systems were conducted by the application of different preparation routes by varying the experimental parameters and the initial compositions of the starting mixtures. Although no crystal structure of a ternary phase in these systems could be solved, there are indications that such phases exist, but further investigations are needed. [1] M. Döch, A. Hammerschmidt, B. Krebs, Z. Anorg. Allg. Chem., 2004, 630, 519. [2] H. Huppertz, Chem. Commun., 2011, 47, 131; and references therein. [3] J. Hunger, M. Borna, R. Kniep, J. Solid State Chem., 2010, 182, 702; J. Hunger, M. Borna, R. Kniep, Z. Kristallogr. NCS, 2010, 225, 217; M. Borna, J. Hunger, R. Kniep, Z. Kristallogr. NCS, 2010, 225, 223; M. Borna, J. Hunger, R. Kniep, Z. Kristallogr. NCS, 2010, 225, 225. [4] M. Borna, J. Hunger, A. Ormeci, D. Zahn, U. Burkhardt, W. Carrillo-Cabrera, R. Cardoso-Gil, R. Kniep, J. Solid State Chem., 2011, 184, 296; [5] H. Müller-Bunz, T. Nikelski, Th. Schleid, Z. Naturforsch. B, 2003, 58, 375. [6] H. U. Bambauer, J. Weidelt, J.-St. Ysker, Z. Kristallogr., 1969, 130, 207. [7] D. de Saint-Giniez, P. Laruelle, J. Flahaut, C. R. Séances, Acad. Sci. Ser. C, 1968, 267, 1029.

No description available.

En Guinée, la disponibilité des ressources en eau est soumise à de graves problèmes de gestion avec des conséquences importantes pour les populations, notamment à Kankan où la plupart des puits tarissent pendant la saison sèche, et où la fourniture régulière de l’eau à partir de la rivière Milo n'est pas assurée dans tous les quartiers de la ville. Le Milo et son bassin versant représente donc un enjeu important pour les habitants de cette ville. Le Milo (480 km de long) qui draine un bassin versant 13 810 km2 est le plus important des affluents rive droite du Niger. Pour évaluer l’impact du bassin versant du Milo et de la ville de Kankan sur la qualité des eaux et des sédiments de ce cours d’eau, 30 échantillons de sédiments de fond ont été prélevés au cours d’une première campagne (juin-juillet 2013) sur l’ensemble des cours d’eau du bassin versant, tandis que durant une deuxième campagne (avril 2014-mai 2015), un suivi régulier a été mis en place sur le Milo en amont et en aval de Kankan. Au cours de cette dernière, 232 échantillons d’eau du Milo (dont 116 utilisés pour l’isotopie), et 26 échantillons de sédiments de fond ont été prélevés sur les stations de Bordo (amont de Kankan) et de Karifamoriah (aval de Kankan). Les concentrations en éléments majeurs et traces, terres rares, COP, COD, pH, alcalinité, l’azote organique, les isotopes de l’oxygène et de l’hydrogène, ainsi que la micro-granulométrie des sédiments ont été mesurés. Les résultats obtenus durant le cycle hydrologique 2014-2015 ont permis d’estimer le flux de matières exportées en solution par le Milo à Kankan à 47 863 t.an-1 et le flux de matières particulaires à 76 759 t.an-1. 92% de ce tonnage est exporté durant la période des hautes eaux. Ces flux permettent d’estimer des vitesses moyennes d’érosion physique (8 t.km-2.an-1) et d’altération chimique (5 t.km-2.an-1) du bassin relativement faibles. Le flux spécifique de CO2 consommé par l’altération chimique est lui aussi relativement faible (76.103 mole.km-2.an-1), mais il reste dans la moyenne des flux de CO2 mesurés sur les bassins couverts de sols latéritiques. Le degré de contamination des sédiments et sa variation spatio-temporelle ont été évalués grâce au calcul du facteur d’enrichissement (FE), en normalisant les concentrations en éléments traces par rapport à Al, Sc et Ti et en prenant le PAAS et l’UCC comme matériaux de référence. La quasi-totalité des éléments traces proviennent essentiellement des processus d’altération et sont d’origine naturelle. Toutefois, un enrichissement modéré à significatif (5 < FE < 20) a été mis en évidence pour Zr et Hf (enrichissements naturels) et As et Sb (impacts anthropiques). Finalement, l’apport anthropique en éléments traces, quand il existe, reste modéré. Les profils de concentrations en terres rares ont permis de montrer que la signature géochimique des sédiments de fond du Milo est homogène sur l’ensemble du bassin et caractéristique des sols latéritiques, non perturbée par la ville de Kankan et elle est proche des signatures du PAAS et de l’UCC. Pour l’ensemble des éléments traces et des terres rares la contribution anthropique reste faible et les fractions disponibles (phases labiles) sur les sédiments (extraction à l’EDTA) sont également faibles, confirmant ainsi que l’essentiel de ces éléments rentrent principalement dans la composition des phases résiduelles. / In Guinea, the availability of water resources is subjected to serious problems of management with important consequences for the populations, particularly in Kankan city where most of the wells dry up during the dry season and where the water supply from the Milo river is not assured for all the districts. Then the Milo river and its watershed represent an important issue for the inhabitants of Kankan. The Milo river (480 km in length) which drains an area of 13 810 km2 is the most important right-bank tributary of the Niger river. To evaluate the impact of the Milo watershed and of the Kankan city on the water and sediments of this river, 30 samples of bottom sediments have been collected during a first campaign (June-July 2013) on the main course from upstream to downstream and on the main tributaries, whereas during a second campaign (April 2014-May 2015) a regular monitoring was set up on the Milo river, upstream and downstream Kankan city. During this campaign, 232 river water samples (of which 116 for isotopic analyses) and 26 bottom sediment samples have been collected at Bordo (upstream) and Karifamoriah (downstream) stations. The concentrations of major and trace elements, rare earth elements, POC and PON, DOC, pH, alkalinity, the isotopic composition of O, H and the micro-granulometry of sediments have been measured. The results obtained during the hydrological cycle 2014-2015 allowed to estimate the fluxes of dissolved (47 863 t.y-1) and particulate (76 759 t.y-1) matters exported by the Milo river at Kankan. 92% of these fluxes are exported during the high flow period. These fluxes allowed us to estimate very low average rates of physical erosion (8 t.km-2.y-1) and chemical weathering (5 t.km-2.y-1) of the Milo catchment. The specific flux of CO2 consumed by chemical weathering (76.103 mole.km-2.y-1) is relatively low but within the range of CO2 fluxes measured in catchments draining lateritic soils. The degree of sediment contamination and its spatio-temporal variation have been assessed using the enrichment factor (EF), by normalizing the trace element concentrations with Al, Sc and Ti and by taking PAAS and UCC as the reference materials. Almost all the trace elements mainly originate from weathering processes and are of natural origin. Nevertheless, moderate to significant enrichments (5 < EF < 20) have been calculated for Zr and Hf (natural enrichments) and As and Sb (anthropogenic impacts). Finally, the anthropogenic contribution of trace elements, when it exists, remains moderate. The rare earth concentration patterns allowed to show the geochemical signature of river bottom sediments is homogeneous within the Milo catchment and characteristic of lateritic soils, non- perturbed by the city of Kankan and close to the PAAS and UCC patterns. For most of the trace and rare earth elements, the anthropogenic contribution remains low and the available fractions (labile phases) in the sediment (EDTA extraction) are also low, confirming that the main part of these elements are mainly in the residual phases.

aaaaaRare earth elements (Sc, Y and group 15 lanthanides) and their compounds currently have significant practical use in metallurgy, glass industry, as highly active catalysts for the production of so-called. NiMH batteries, alloys for the manufacture of permanent magnets and e.g. moderators rods in the nuclear energy, but above all they have an irreplaceable role in modern electronics for phosphors TV screens, CRT earlier today, PDP and LCD monitors and displays, tablets, mobile phones etc., which give them a high-quality picture and sound. Unlike most base and precious metals are concentrated in the conquerable ore deposits, occur in the form of compounds as part of mixed minerals in the rarely economically exploitable concentrations, a mining and processing is costly and negative impacts on the environment, paradoxically towards the title but their overall content in the crust is relatively high, the average concentration in the range of about 150 to 220 ppm. The main world producer of REE, China, in 2010, significantly reduced exports by 40 %, making prices of some REE increased up to 1500 % during the month. Demand for REE is growing, so often talks about the recycling of valuable materials back into production, as called. "Urban mining", ie "urban mining", thereby reducing the amount of...

It is known that boron containing compounds exhibit interesting chemical and physical properties. In the past 50 years modern preparative methods have led to an overwhelming number of different structures of novel and often unexpected boron–sulfur and boron–selenium compounds. Among all these new compounds, there was only one which comprises rare earth metal (RE), boron and heavier chalcogen, namely sulfur, the europium thioborate Eu[B2S4] [1]. Selenoborates of rare earth metals are hitherto unknown. On the other hand, rare earth oxoborates represent a well-known class of compounds [2] with a wide range of applications, especially in the field of optical materials. In addition, well-defined boron compounds containing the heavier group 16 elements are fairly difficult to prepare due to the high reactivity of in situ formed boron chalcogenides towards most container materials at elevated temperatures. The chalcogenoborates of the heavier chalcogens are sensitive against oxidation and hydrolysis and therefore have to be handled in an inert environment. Therefore, developing and optimization of preparative routes for the syntheses of pure and crystalline RE thio- and selenoborates was needed. In the course of this study, the application of different preparation routes, such as optimized high-temperature routes (HT), metathesis reactions and high-pressure high-temperature routes (Hp – HT), led to sixteen new rare earth thioborates. Their crystal structures were solved and/or refined from powder and single crystal X-ray diffraction data, while the local structure around rare earth metal was confirmed from the results of the EXAFS analyses. Quantum mechanical calculations were used within this work in order to investigate the arrangement of intrinsic vacancies on the boron sites in the crystal structures of rare earth thioborates. Thermal, magnetic and optical properties of these compounds are also discussed. The rare earth thioborates discovered during this work are the first examples of ternary thioborates containing trivalent cations. These compounds can be divided into two groups of isotypic compounds: the rare earth orthothioborates with general formula REIII[BS3] (RE = La – Nd, Sm, Gd and Tb) [3] and the rare earth thioborate sulfides with general formula REIII¦9B5S21, (RE = Gd – Lu, and Y) [4]. In the crystal structure of RE[BS3] (orthorhombic, space group Pna21, Z = 4), the sulfur atoms form the vertices of corrugated kagome nets, within which every second triangle is occupied by boron and the large hexagons are centered by RE cations. The structural features of the isotypic RE[BS3] phases show great similarities to those of rare earth oxoborates RE[BO3] and orthothioborates of alkali and alkaline earth metals as well as to thallium orthothioborate, yet pronounced differences are also observed: the [BS3]3– groups in the crystal structures of RE[BS3] are more distorted, where the distortion decreases with the decreasing size of the RE element, and the coordination environments of the [BS3]3– groups in the crystal structures of RE[BS3] are different in comparison with the coordination environments of the [BO3]3– groups in the crystal structures of λ-Nd[BO3] [5] and of o-Ce[BO3] [6]. The results of the IR and Raman investigations are in agreement with the presence of [BS3]3– anions in the crystal structure of RE[BS3]. Thermal analyses revealed the thermal stability of these compounds under inert conditions up to ~ 1200 K. Analyses of the magnetic properties of the Sm, Gd and Tb thioborates showed that both Gd and Tb phases order antiferromagnetically. The magnetic susceptibility for Sm orthothioborate approximately follows the Van-Vleck theory for Sm3+. Between 50 K and 62 K a transition appears which is independent of the magnetic field: the magnetic susceptibility becomes lower. This effect might indicate a discontinuous valence transition of Sm which was further investigated by means of XANES and X-ray diffraction using synchrotron radiation, both at low temperatures. The series of isotypic RE thioborate sulfides with composition RE9B5S21, was obtained by the application of Hp – HT conditions to starting mixtures with the initial chemical composition “REB3S6“, after careful optimization of the pressure, temperature and treatment time, as well as the composition of the starting mixtures. Their crystal structures adopt the Ce6Al3.33S14 [7] structure type (hexagonal, space group P63, Z = 2/3). The special features of the RE9B5S21 crystal structures, concerning boron site occupancies and different coordination environments of the two crystallographically independent boron sites, were investigated in more detail by means of quantum chemical calculations, electron diffraction methods, optical and X-ray absorption spectroscopy as well as by 11B NMR spectroscopy. The results obtained from these different experimental and computational methods are in good mutual agreement. The crystal structures of the RE9B5S21 compounds are characterized by two types of anions: tetrahedral [BS4]5– and trigonal planar [BS3]3– as well as [(S2–)3] units. Isolated [BS4]5– tetrahedra (all pointing with one of their apices along the polar [001] direction) represent a unique feature of the crystal structure which is observed for the first time in a thioborate compound. These tetrahedra are stacked along the three-fold rotation axes. Vacancies are located at the trigonal-planar coordinated boron site with preferred ordering –B–B––B–B–– along [001]. No superstructure is observed by means of electron diffraction methods as adjacent columns are shuffled along the c axis, giving rise to a randomly distributed vacancy pattern. Positions of the sulfur atoms within the [(S2–)3] substructure as well as planarity of the [BS3]3– units were investigated in more detail by means of quantum mechanical calculations. Results of the IR and Raman spectroscopy, as well as of the 11B NMR spectroscopy are in agreement with the presence of the boron atoms in two different coordination environments. Thermal analyses showed that compounds RE9B5S21 are stable under inert conditions up to ~ 1200 K. In accordance with the combined results of experimental and computational investigations, the chemical formula of the RE9B5S21 compounds is consistent with RE3[BS3]2[BS4]3S3. A short overview of investigations towards rare earth selenoborates, where in most of the cases only known binary rare earth selenides could be identified, is presented as well in this work. Investigations in the RE–B–Se systems were conducted by the application of different preparation routes by varying the experimental parameters and the initial compositions of the starting mixtures. Although no crystal structure of a ternary phase in these systems could be solved, there are indications that such phases exist, but further investigations are needed. [1] M. Döch, A. Hammerschmidt, B. Krebs, Z. Anorg. Allg. Chem., 2004, 630, 519. [2] H. Huppertz, Chem. Commun., 2011, 47, 131; and references therein. [3] J. Hunger, M. Borna, R. Kniep, J. Solid State Chem., 2010, 182, 702; J. Hunger, M. Borna, R. Kniep, Z. Kristallogr. NCS, 2010, 225, 217; M. Borna, J. Hunger, R. Kniep, Z. Kristallogr. NCS, 2010, 225, 223; M. Borna, J. Hunger, R. Kniep, Z. Kristallogr. NCS, 2010, 225, 225. [4] M. Borna, J. Hunger, A. Ormeci, D. Zahn, U. Burkhardt, W. Carrillo-Cabrera, R. Cardoso-Gil, R. Kniep, J. Solid State Chem., 2011, 184, 296; [5] H. Müller-Bunz, T. Nikelski, Th. Schleid, Z. Naturforsch. B, 2003, 58, 375. [6] H. U. Bambauer, J. Weidelt, J.-St. Ysker, Z. Kristallogr., 1969, 130, 207. [7] D. de Saint-Giniez, P. Laruelle, J. Flahaut, C. R. Séances, Acad. Sci. Ser. C, 1968, 267, 1029.:I INTRODUCTION ......................................................................... 7 1. Motivation and scope of the work .............................................. 9 2. Literature overview .................................................................. 11 2.1. The binary subsystems of the ternary systems RE–B–Q (RE = rare earth metals, Y; Q = S, Se) ......................................................... 12 2.1.1. RE–Q ............................................................................... 12 2.1.2. RE–B ............................................................................... 19 2.1.3. B–Q ................................................................................. 22 2.2. Related ternary compounds ................................................... 25 2.2.1. RE oxoborates .................................................................. 25 2.2.2. Thio- and selenoborates of alkaline, alkaline earth, transition and post transition metals ......................................................................... 33 2.2.3. The RE thioborate Eu[B2S4]................................................ 45 II PREPARATIVE METHODS AND EXPERIMENTAL TECHNIQUES .......... 47 1. Starting materials and their characterization ............................... 49 2. Synthetic approaches and optimizations .................................... 51 2.1. High-temperature routes ...................................................... 52 2.2. Metathesis reactions ............................................................ 53 2.3. Spark Plasma Sintering (SPS) ............................................... 54 2.4. High-Pressure High-Temperature (Hp – HT) Syntheses ........... 55 3. Analytical methods and samples characterization ....................... 55 3.1. Powder X-ray diffraction ...................................................... 55 3.2. Crystal structure investigations using synchrotron radiation .... 57 3.3. Single crystal X-ray diffraction analysis .................................. 57 3.4. Metallographic investigations ................................................ 58 3.5. Electron microscopy ............................................................ 58 3.5.1. Scanning electron microscopy and energy dispersive X-ray spectroscopy ............................................................................ 58 3.5.2. Transmission electron microscopy ...................................... 59 3.6. Optical spectroscopy ........................................................... 59 3.6.1. Infra-Red spectroscopy .................................................... 59 3.6.2. Raman spectroscopy ........................................................ 60 3.7. X-ray absorption spectroscopy ............................................ 60 3.8. Thermal analysis ................................................................. 62 3.9. Magnetic susceptibility measurements ................................... 63 3.10. 11B NMR spectroscopy ..................................................... 63 3.11. Quantum chemical calculations ........................................... 64 3.11.1. Total energy calculations ................................................ 64 3.11.2. Charge transfer analysis ................................................ 64 3.11.3. Chemical bonding........................................................... 64 III RARE EARTH THIOBORATES ................................................. 67 1. Reinvestigation of the only reported rare earth thioborate – EuB2S4 ....69 2. RE[BS3] (RE = La – Nd, Sm, Gd, Tb) .................................... 69 2.1. Syntheses and phase analyses .......................................... 70 2.2. Crystal structure determinations ........................................ 74 2.3. X-ray absorption spectroscopy: EXAFS data analysis for Pr[BS3] ..... 79 2.4. Crystal chemistry .............................................................. 80 2.5. Optical spectroscopy ......................................................... 83 2.6. Thermal analysis ............................................................... 86 2.7. Magnetic susceptibility ....................................................... 88 2.8. X-ray absorption spectroscopy: XANES data analysis for Sm[BS3] .. 91 2.9. Crystal structure investigation at low temperature using synchrotron radiation ................................................................................... 91 2.10. Summary ......................................................................... 95 3. Gd[BS3] : Ce, Eu, Tb ............................................................. 97 3.1. Syntheses and phase analyses ............................................. 97 3.2. Crystal structure determinations ......................................... 101 3.3. Crystal chemistry .............................................................. 103 3.4. Optical spectroscopy ......................................................... 104 3.5. Thermal analysis ............................................................... 106 3.6. Summary ......................................................................... 107 4. RE9B5S21 (RE = Tb – Lu, Y) ................................................ 107 4.1. Syntheses and phase analyses ........................................... 108 4.2. Crystal structure determinations ........................................ 109 4.3. Crystal chemistry .............................................................. 112 4.4. Electronic structure, charge transfer and chemical bonding .... 115 4.5. X-ray absorption spectroscopy: EXAFS data analysis for Lu9B5S21 .............................................................................. 119 4.6. Thermal analysis ............................................................... 121 4.7. 11B NMR investigations ..................................................... 122 4.8. Optical spectroscopy ......................................................... 123 4.9. Summary ......................................................................... 126 IV ON THE WAY TO RARE EARTH SELENOBORATES .................... 127 1. Towards ternary phases in the systems RE–B–Se, with RE = Sm, Tb – Lu.......................................................................................... 129 2. The system La–B–Se ........................................................... 134 3. The system Gd–B–Se .......................................................... 136 4. The system Y–B–Se ............................................................ 137 5. Summary ........................................................................... 139 V SUMMARY AND OUTLOOK ..................................................... 141 VI APPENDIX .......................................................................... 149 VII REFERENCES .................................................................... 163 VIII LIST OF FIGURES ............................................................. 181 IX LIST OF TABLES ................................................................ 193 X CURRICULUM VITAE ........................................................... 199 XI VERSICHERUNG ............................................................... 203

Le but principal de cette étude est de comprendre le fonctionnement de la zone interface, continuum terre-mer au Liban. Suite à l’anthropisation spécifiquement la construction des barrages, les apports du fleuve vers la mer en termes de quantité et qualité, sont modifiés de nos jours. Le fleuve Ibrahim, ayant le débit le plus important parmi les fleuves libanais, interrompu par trois barrages, a été choisi comme étude de cas représentant les fleuves côtiers libanais. Les différents paramètres retenus ont permis de dégager des résultats intéressants. Au niveau de l’eau de surface marine le panache fluvial est décelé par l’étude des paramètres hydrologiques des masses d’eaux superficielles. Les résultats montrent aussi que l’apport fluviatile est le contributeur principal en nutriments au niveau de la région côtière durant la saison humide, élucidé par les teneurs en nitrates et silice dissoute. D’autre part, le transfert des particules de la zone côtière vers le large, à travers la pente continentale, se fait par l’intermédiaire de couches néphéloïdes.L’origine des sédiments et de leurs constituants est mise en relief en analysant plusieurs paramètres sédimentaires. La combinaison des paramètres granulométriques et géochimiques organiques et inorganiques et l’application des tests statistiques a permis de distinguer entre deux environnements de dépôt. (1) Les environnements littoraux (≤ 30 m) ou zone de « bypass » où le sable fin et la matière organique autochtone dominent. (2) Les environnements profonds (≥ 60 m) ou zones de dépôts où la fraction fine et la matière organique allochtone dominent.Sur l’ensemble du suivi l’état chimique de l’eau du fleuve au niveau des deux stations échantillonnées, déduit des teneurs en nutriments et macrofaune benthique, est considéré comme bon à très bon d’après les normes internationales Finalement, l’analyse des éléments traces métalliques confirme la faible contribution anthropique dans les stations marines et fluviatiles échantillonnées malgré la densité de population croissante au niveau de la région côtière Libanaise. / The main purpose of this study is to understand the functioning of the coastal zone, land-sea continuum in Lebanon. Following the construction of dams, the contributions of the river towards the sea in terms of quantity and quality, are modified nowadays. The Ibrahim river, having the highest flow among the Lebanese rivers, interrupted by three dams, was chosen as a case study representing the Lebanese coastal rivers. The various parameters retained made it possible to obtain interesting results. At sea surface water level, the river plume is detected by studying the hydrological parameters of surface water.The results also show that the river is the main nutrient contributor in the coastal region during the wet season, elucidated by the nitrate and dissolved silica contents. On the other hand, the transfer of particles from the coastal zone to the open sea, across the continental slope, takes place through the nepheloid layers.The origin of sediments and their constituents is highlighted by analyzing several sediment parameters. The combination of organic and inorganic particle size and geochemical parameters and the application of statistical tests made it possible to distinguish between two deposition environments. (1) Coastal environments (≤ 30 m) or “bypass” area where fine sand and autochtonous organic matter dominate. (2) Deep environments (≥ 60 m) or deposit areas where the fine fraction and allochthonous organic matter dominate.The ecological state of the river water at the two sampled stations, deduced from the contents of nutrients and benthic macrofauna, is considered good to very good according to international standards. Finally, the analysis of metallic trace elements confirms the low anthropogenic contribution in the marine and river stations despite the increasing density of the population in the Lebanese coastal region.

No description available.