Aluminium titanium oxynitrides were studied as candidate materials for high temperature absorbers in solar selective coatings due to their excellent stability and their tuneable optical behaviour. A set of individual AlyTi1-y(OxN1-x) layers with different oxygen content was prepared by cathodic vacuum arc (CVA) deposition. The composition, morphology, phase structure and microstructure of the films were characterized by elastic recoil detection (ERD), scanning and transmission electron microscopy and X-ray diffraction. An fcc phase structure is found in a broad compositional range of AlyTi1-y(OxN1-x). Simultaneously, sample microstructure and morphology undergo systematic changes from a columnar growth to the development of a heterogeneous structure with spherical nanoparticle inclusions when the oxygen concentration is increased. The optical properties were determined by spectroscopic ellipsometry and UV–Vis–NIR and FTIR spectrophotometry. A comprehensive analysis of the film properties allowed an accurate modelling of the optical constants of the AlyTi1-y(OxN1-x) in the whole wavelength range of solar interest (from 190 nm to 25 µm). It points to a transition from metallic to dielectric behaviour with increasing oxygen content. Consequently, it is demonstrated that the optical properties of these AlyTi1-y(OxN1-x) deposited films can be controlled in a wide range from metallic to dielectric character by adjusting the oxygen concentration, opening a huge range of possibilities for the design of solar selective coatings (SSC) based on this material. Complete SSC, including a TiN layer as IR reflector, were designed by applying optical simulations, obtaining excellent optical selective properties of α=94.0% and εRT = 4.8%.

No description available.

Mixed anion systems, such as oxynitrides and oxyfluorides, are an emerging class of interesting materials. The lower stability of mixed anion systems in comparison to oxide materials has had the consequence that this area of materials research is relatively less well explored. However, the development of new synthesis techniques has resulted in the preparation of many new mixed anion systems and so a detailed understanding of their structure and how this relates to their electronic and magnetic properties is necessary. Within this Thesis, several oxide, oxynitride and oxyfluoride systems are investigated with a particular focus on the magnetic behaviour of materials based on geometrically frustrated pyrochlore and kagome lattices. The Lu2Mo2O7 pyrochlore contains a geometrically frustrated network of vertex sharing Mo4+ (d2 S = 1) tetrahedra. Here, the solid state synthesis of Lu2Mo2O7−x is reported along with a discussion of the coexistence of two cubic pyrochlore phases that has been discovered in samples synthesised at 1600 ◦C. Powder neutron diffraction and thermogravimetric analysis have revealed that this two-phase behaviour originates from a miscibility gap between stoichiometric Lu2Mo2O7 and oxygen deficient Lu2Mo2O6.6. Magnetic susceptibility and muon spin relaxation measurements support the formation of a geometrically frustrated spin glass ground state in Lu2Mo2O7 with a spin freezing temperature Tf ∼ 16 K. Low temperature neutron diffraction has confirmed the absence of long range magnetic order and magnetic diffuse neutron scattering data have indicated the presence of competing nearest and next nearest neighbour antiferromagnetic exchange interactions in the spin glass state. The magnetic heat capacity of Lu2Mo2O7 follows a T2-dependence at the low temperatures, indicating that Lu2Mo2O7 is another rare example of an unconventional, topological spin glass, which is stable in the absence of significant chemical disorder. The magnetic properties of the oxygen deficient pyrochlore phase Lu2Mo2O6.6 are qualitatively similar to those of Lu2Mo2O7, but an increase in the spin freezing temperature Tf ∼ 20 K suggests that oxygen-vacancy disorder in Lu2Mo2O6.6 favours the onset of a glassy state at higher temperatures and enhances the degree of frustration. Oxynitride pyrochlores with the ideal composition R2Mo2O5N2 (R = rare earth) contain Mo5+ d1 S = 1 2 cations on the frustrated pyrochlore lattice and are thus ideal candidates to support exotic magnetic ground states. Here, the synthesis of oxynitride pyrochlores of the Lu2Mo2O7 system by thermal ammonolysis is discussed alongside powder neutron diffraction and susceptibility data that show no evidence for long range magnetic order and an absence of spin freezing down to at least 2 K despite the persistence of strong antiferromagnetic exchange (θ = −120 K). A comparison of the magnetic diffuse neutron scattering between the spin glass state of Lu2Mo2O7 and the oxynitride is given, which suggests that the majority of the magnetic scattering in the oxynitride system is inelastic. In addition, low temperature magnetic heat capacity shows an absence of magnetic phase transitions and a continuous density of states through a T-linear dependence down to 500 mK. [NH4]2[C7H14N][V7O6F18], diammonium quinuclidinium vanadium(III,IV) oxyfluoride or DQVOF, is a kagome bilayer system with a geometrically frustrated two-dimensional kagome network of V4+ d1 S = 1 2 cations and V3+ d2 S = 1 cations between the kagome layers. Here, low temperature magnetisation and heat capacity data are presented, which demonstrate that the interplane V3+ d2 cations are well decoupled from the kagome layers at low temperatures such that DQVOF is a good experimental realisation of a S = 1 2 kagome antiferromagnet. Despite significant antiferromagnetic exchange (θ = −60 K) within the kagome planes, muon spin relaxation data have confirmed the absence of spin freezing and the persistence of internal field fluctuations that are intrinsic to the kagome layers down to temperatures of 40 mK. The low temperature heat capacity of the V4+ kagome network follows T-linear behaviour down to the 300 mK, highlighting the absence of a spin gap in the low energy excitation spectrum of DQVOF. The low temperature magnetic study of DQVOF presented here thus strongly supports the formation of a gapless quantum spin liquid phase. In the final results chapter, a discussion of the anion ordering principles in oxynitride systems is given. A high temperature, high resolution neutron diffraction study of the oxynitride perovskite SrTaO2N has revealed that the partial anion order that results in segregated Ta-N zig-zag chains is stable up to 1100 ◦C. Furthermore, these anion ordering principles are extended to the d1 perovskite oxynitrides RVO2−xN1+x (R = La, Nd, Pr) in a variable temperature neutron diffraction study, which confirms that the anion chain ordering discovered in d0 SrTaO2N is robust to electron doping. The R = La analogue also provides an interesting example of a rhombohedral oxynitride perovskite phase which coexists with an orthorhombic phase over the 4−300 K temperature range of the neutron diffraction study.

Mixed metal oxynitrides have attracted attention due to their interesting chemical and physical properties in the past twenty years. In this thesis, four series of mixed metal oxynitrides have been investigated. The samples have been synthesized by both thermal ammonolysis and high pressure high temperature methods. The structural exploration covers perovskite, scheelite and pyrochlore types. The structural studies were carried out using powder X-ray and neutron diffraction, and magnetic and conducting properties have been explored. A series of new RZrO2N (R = Pr, Nd and Sm) perovskites were synthesized using high pressure high temperature methods (HPHT) via a direct solid state reaction of R2O3 with Zr2ON2. All three new phases crystallize in the orthorhombic Pnma perovskite superstructure, and the structural distortion increases with decreasing R3+ ionic radius. RZrO2N contains both R3+ and d0 Zr4+ and thus shows a potential for multiferroic properties. EuWO1-xN2+x perovskites with a wide range of nitrogen contents (-0.16 ≤ x ≤ 0.46) were synthesized by thermal ammonolysis of an oxide precursor Eu2W2O9. Ferromagnetic ordering below a Curie temperature TC =12 ± 1 K and negative colossal magnetoresistances (CMR) have been discovered in these samples. In particular, for the lowest doped sample, EuWO0.96N2.04, CMR ≥ 99.7% was observed at 7 K. The possibility of tuning the physical properties by altering the chemical composition has been demonstrated. A linear relationship between the lattice parameter and nitrogen content of EuWO1+xN2-x was observed. An investigation has been made of the Eu-Mo-O-N system. A new pyrochlore oxynitride series Eu2Mo2O6-xN2+2x/3 (0.20 ≤ x ≤ 2.25) was synthesized by ammonolysis of Eu2Mo2O7. A ferrimagnetic ordering and semiconducting behavior has been observed in these samples. A detailed structural study of SrMO2N (M = Nb, Ta) has been performed using variable temperature neutron and electron diffraction. Partial anion order has been observed in both samples up to 750 oC. It is consistent with cis-ordering of the two nitrides in each MO4N2 octahedron. At low temperatures, this order directs the tilting of the octahedron to form a pseudo-tetragonal superstructure. It creates zig-zag MN chains in two or three dimensions within the lattice. This principle can be used to predict the local structures of perovskite-related oxynitrides AMO3-xNx.

Neste trabalho foram crescidos filmes finos de oxinitreto de silício (SiOxNy) por processamento térmico rápido (RTP) utilizando um forno térmico convencional adaptado, objetivando fabricar células solares MOS com baixo custo agregado e bom rendimento de conversão de baixas intensidades luminosas em energia elétrica de forma reprodutível. A receita de oxinitretação otimizada foi desenvolvida em ambiente misto de 5N2:1O2 na temperatura de 850°C para tempos de processo, na faixa de 10 a 80s seguido por uma passivação em 2L/min de N2 por 80s. Os dielétricos crescidos foram caracterizados fisicamente quanto à espessura (entre 1,50 e 2,95nm), à microrugosidade (<0,95nmRMS) e à concentração de nitrogênio (1,0-2,1%atm). As características de tunelamento foram investigadas em capacitores MOS e apontaram para a existência de armadilhas interfaciais do tipo K capazes de armazenar cargas positivas. Nas células solares MOS, a corrente de fundo foi característica para todos os processos de oxinitretação empregados (~0,5-2µA/cm2) e apresentaram níveis de resposta à luz incidente na faixa de 1 a 8mA/cm2 compatível com aplicações de conversão de energia em ambientes internos e externos (energy harvesting). A característica densidade de corrente x tensão de porta (JxVG) das células solares apresentou um comportamento aproximadamente linear desde a densidade de corrente de curto-circuito (JSC) até a tensão de curto-circuito (VOC) implicando em potência gerada máximas (PGmáx) de até centenas de µA/cm2 para VG ? VOC/2 para uma ampla faixa de intensidade radiante incidente (11,8 - 105,7mW/cm2) alcançando rendimentos de conversão de até 5,5%. / In this work, silicon oxynitrides (SiOxNy) were grown by means of a homemade Rapid Thermal Processing (RTP). The goal was to manufacture MOS solar cells with a reduced price and reasonable light conversion efficiency for low light intensity. The optimized oxidation recipe consisted of using an environment with gas mixture of 5N2:1O2 at a temperature of 850°C and different processing times in the range of 10 to 80s followed by a passivation step in ultrapure N2 (2L/min) at the same temperature of 850oC for 80s. The oxynitrides were grown with thickness in the range of 1.50 to 2.95nm with surface microroughness lower than 0.95nmRMS and nitrogen concentration in the range of 1.0 to 2.1%atm. The tunneling characteristics were studied with the aid of MOS capacitor and K-type interfacial traps related to Si(p)/Si?N structure were detected positively charged for VG > 0. The background current in the MOS solar cells (~0.5-2µA/cm2) were similar for all samples and the current response to the incident light was in the range of 1 to 8mA/cm2, which is compatible with energy conversion for indoor and outdoor environments (energy harvesting). The current density x gate voltage (JxVG) characteristics of the MOS solar cells presented a nearly linear behavior since the short-circuit current density (JSC) till to the open circuit voltage (VOC) so that the maximum generated power was of hundreds of µA/cm2 for VG ? VOC/2 for a large range of radiant intensities (11.8 - 105.7 mW/cm2) and achieving efficiency conversion up to 5.5%.

Neste trabalho foram crescidos filmes finos de oxinitreto de silício (SiOxNy) por processamento térmico rápido (RTP) utilizando um forno térmico convencional adaptado, objetivando fabricar células solares MOS com baixo custo agregado e bom rendimento de conversão de baixas intensidades luminosas em energia elétrica de forma reprodutível. A receita de oxinitretação otimizada foi desenvolvida em ambiente misto de 5N2:1O2 na temperatura de 850°C para tempos de processo, na faixa de 10 a 80s seguido por uma passivação em 2L/min de N2 por 80s. Os dielétricos crescidos foram caracterizados fisicamente quanto à espessura (entre 1,50 e 2,95nm), à microrugosidade (<0,95nmRMS) e à concentração de nitrogênio (1,0-2,1%atm). As características de tunelamento foram investigadas em capacitores MOS e apontaram para a existência de armadilhas interfaciais do tipo K capazes de armazenar cargas positivas. Nas células solares MOS, a corrente de fundo foi característica para todos os processos de oxinitretação empregados (~0,5-2µA/cm2) e apresentaram níveis de resposta à luz incidente na faixa de 1 a 8mA/cm2 compatível com aplicações de conversão de energia em ambientes internos e externos (energy harvesting). A característica densidade de corrente x tensão de porta (JxVG) das células solares apresentou um comportamento aproximadamente linear desde a densidade de corrente de curto-circuito (JSC) até a tensão de curto-circuito (VOC) implicando em potência gerada máximas (PGmáx) de até centenas de µA/cm2 para VG ? VOC/2 para uma ampla faixa de intensidade radiante incidente (11,8 - 105,7mW/cm2) alcançando rendimentos de conversão de até 5,5%. / In this work, silicon oxynitrides (SiOxNy) were grown by means of a homemade Rapid Thermal Processing (RTP). The goal was to manufacture MOS solar cells with a reduced price and reasonable light conversion efficiency for low light intensity. The optimized oxidation recipe consisted of using an environment with gas mixture of 5N2:1O2 at a temperature of 850°C and different processing times in the range of 10 to 80s followed by a passivation step in ultrapure N2 (2L/min) at the same temperature of 850oC for 80s. The oxynitrides were grown with thickness in the range of 1.50 to 2.95nm with surface microroughness lower than 0.95nmRMS and nitrogen concentration in the range of 1.0 to 2.1%atm. The tunneling characteristics were studied with the aid of MOS capacitor and K-type interfacial traps related to Si(p)/Si?N structure were detected positively charged for VG > 0. The background current in the MOS solar cells (~0.5-2µA/cm2) were similar for all samples and the current response to the incident light was in the range of 1 to 8mA/cm2, which is compatible with energy conversion for indoor and outdoor environments (energy harvesting). The current density x gate voltage (JxVG) characteristics of the MOS solar cells presented a nearly linear behavior since the short-circuit current density (JSC) till to the open circuit voltage (VOC) so that the maximum generated power was of hundreds of µA/cm2 for VG ? VOC/2 for a large range of radiant intensities (11.8 - 105.7 mW/cm2) and achieving efficiency conversion up to 5.5%.

The durability of two solar-selective aluminium titanium oxynitride multilayer coatings was studied under conditions simulating realistic operation of central receiver power plants. The coatings were deposited by cathodic vacuum arc applying an optimized design concept for complete solar-selective coating (SSC) stacks. Compositional, structural and optical characterization of initial and final stacks was performed by scanning electron microscopy, elastic recoil detection, UV-Vis-NIR-IR spectrophotometry and X-Ray diffraction. The design concept of the solar selective coatings was validated by an excellent agreement between simulated and initial experimental stacking order, composition and optical properties. Both SSC stacks were stable in single stage tests of 12 hours at 650°C. At 800°C, they underwent a structural transformation by full oxidation and they lost their solar selectivity. During cyclic durability tests, multilayer 1, comprised of TiN, Al0.64Ti0.36N and an Al1.37Ti0.54O top layer, fulfilled the performance criterion (PC) ≤ 5% for 300 symmetric, 3 hours long cycles at 600°C in air. Multilayer 2, which was constituted of four AlyTi1-y(OxN1-x) layers, met the performance criterion for 250 cycles (750 hours), but was more sensitive to these harsh conditions. With regard to the degradation mechanisms, the coarser microstructure of multilayer 1 is more resistant against oxidation than multilayer 2 with its graded oxygen content. These results confirm that the designed SSCs based on AlyTi1-y(OxN1-x) materials withstand breakdown at 600ºC in air. Therefore, they can be an exciting candidate material for concentrated solar power applications at high temperature.

L’acrylonitrile est un intermédiaire de l’industrie chimique pour la synthèse de nombreuxpolymères et revêtements. Il est produit à partir de propène qui devient de plus en plus cher et rare. Ceprojet visait à développer de nouveaux catalyseurs à base de nitrures ou d’oxynitrures permettantd’utiliser le propane moins cher et abondant, qui présente un intérêt industriel vu son potentieléconomique et sa durabilité, puisque son exploitation comme précurseur chimique permettraitd’utiliser plus efficacement les ressources naturelles. De nombreux solides ont été préparés et testéscomme catalyseurs. Certains se sont avérés instables dans les conditions de réaction comme lesoxynitrures VZrON, MoVON, et LaVON. D’autres comme MgTaVON et VZrAlON sont apparusstables mais soit faiblement actifs ou non sélectifs. L’étude s’est focalisée sur les oxynitrures VAlONet leur amélioration. Ils ont été caractérisés par de multiples techniques, telles que la DRX, XES,XANES, XPS, RMN 27Al, TPD NH3 et CO2. L’influence de paramètres tels que le rapport V/Al, lepH, la surface spécifique, le temps de contact ont été étudiés. Le catalyseur optimal possède un rapportV/Al d’environ 0,30. Les études ont permis de montrer que les sites nitrurés impliqués dansl’ammoxydation du propane sont du type OxV-NH2--AlO3 et que le degré d’oxydation moyen duvanadium en condition de catalyse est de 3,8. Une nouvelle méthode de préparation des catalyseurs aété mise au point à partir d’un complexe oxalate de vanadium et d’aluminium qui est décomposé parozonation, et nitruré en conditions réactionnelles. Ce catalyseur s’avère plus actif et sélectif que lescatalyseurs préparés par co-précipitation. / Acrylonitrile is an intermediate of the chemical industry, used for synthesis ofnumerous polymers and coating. It is produced by ammoxidation of propene, which becomes rare andexpensive. This project aimed to develop new catalysts based on nitrides and oxynitrides allowing touse abundant and cheaper propane as starting product. Propane presents an industrial interest in viewof its economical potential and durability and because its exploitation as chemical precursor wouldallow to use natural resources more efficiently. Numerous oxynitrides based catalysts have beenprepared and tested as catalysts. Some of them were shown to be unstable in reaction conditions, likeVZrON, MoVON, and LaVON, some were shown to be stable but either weakly active or notselective like MgTaVON and VZrAlON. The study has been focused on VAlON oxynitrides. Thesecatalysts have been characterized by several techniques, like XRD, XES, XANES, XPS, 27Al-NMR,NH3 and CO2-TDP and the influence of several parameters on their catalytic properties have beenstudied. The results of these studies have confirmed that these catalysts were very efficient for thereaction and shown that the optimal catalyst had a V/Al ratio around 0.30 with an average oxidationstate of vanadium in catalytic condition around 3.8. A nitridation site has been proposed correspondingto OxV-NH2--AlO3 species. Finally a new preparation method has been discovered with the synthesisof an oxalate of vanadium and aluminum complex, which is decomposed by ozonation, and nitrided inreaction conditions. This catalyst showed improved activity and selectivity compared to coprecipitatedcatalysts.

Ein viel diskutiertes Thema unserer Zeit ist die Zukunft der Energiegewinnung und Speicherung. Dabei nimmt die Nanowissenschaft eine bedeutende Rolle ein; sie führt zu einer Effizienzsteigerung bei der Speicherung und Gewinnung durch bereits bekannte Materialien und durch neue Materialien. In diesem Zusammenhang ist die Chemie Wegbereiter für Nanomaterialien. Allerdings führen bisher die meisten bekannten Synthesen von Nanopartikeln zu undefinierten Partikeln. Eine einfache, kostengünstige und sichere Synthese würde die Möglichkeit einer breiten Anwendung und Skalierbarkeit bieten. In dieser Arbeit soll daher die Darstellung der einfachen Synthese von Mangannitrid-, Aluminiumnitrid-, Lithiummangansilicat-, Zirkonium-oxinitrid- und Mangancarbonatnanopartikel betrachtet werden. Dabei werden die sogenannte Harnstoff-Glas-Route als eine Festphasensynthese und die Solvothermalsynthese als typische Flüssigphasensynthese eingesetzt. Beide Synthesewege führen zu definierten Partikelgrößen und interessanten Morphologien und ermöglichen eine Einflussnahme auf die Produkte. Im Falle der Synthese der Mangannitridnanopartikel mithilfe der Harnstoff-Glas-Route führt diese zu Nanopartikeln mit Kern-Hülle-Struktur, deren Einsatz als Konversionsmaterial erstmalig vorgestellt wird. Mit dem Ziel einer leichteren Anwendung von Nanopartikeln wird eine einfache Beschichtung von Oberflächen mit Nanopartikeln mithilfe der Rotationsbeschichtung beschrieben. Es entstand ein Gemisch aus MnN0,43/MnO-Nanopartikeln, eingebettet in einem Kohlenstofffilm, dessen Untersuchung als Konversionsmaterial hohe spezifische Kapazitäten (811 mAh/g) zeigt, die die von dem konventionellen Anodenmaterial Graphit (372 mAh/g) übersteigt. Neben der Synthese des Anodenmaterials wurde ebenfalls die des Kathodenmaterials Li2MnSiO4-Nanopartikeln mithilfe der Harnstoff-Glas-Route vorgestellt. Mithilfe der Synthese von Zirkoniumoxinitridnanopartikeln Zr2ON2 kann eine einfache Einflussnahme auf das gewünschte Produkt durch die Variation derReaktionsbedingungen, wie Harnstoffmenge oder Reaktionstemperatur, bei der Harnstoff-Glas-Route demonstriert werden. Der Zusatz von kleinsten Mengen an Ammoniumchlorid vermeidet, dass sich Kohlenstoff im Endprodukt bildet und führt so zu gelben Zr2ON2-Nanopartikeln mit einer Größe d = 8 nm, die Halbleitereigen-schaften besitzen. Die Synthese von Aluminiumnitridnanopartikeln führt zu kristallinen Nanopartikeln, die in eine amorphe Matrix eingebettet sind. Die Solvothermalsynthese von Mangancarbonatnanopartikel lässt neue Morphologien in Form von Nanostäbchen entstehen, die zu schuppenartigen sphärischen Überstrukturen agglomeriert sind. / The development of new methods toward alternative clean energy production and efficient energy storage is a hot topic nowadays. In this context nanoscience has an important role to find suitable ways of increasing the efficiency of storage and production of energy of already known materials and new materials. However, until now the most well-known syntheses of MnN0,43 and Zr2ON2 nanoparticles lead to undefined particles. A simple, cheap and safe synthesis would offer the possibility of broader applications and scalability. We herein present the so-called urea-glass route which is used as a sol-gel process. This synthetic route leads to well-defined particle sizes, novel particle morphologies and allows the tailoring of the desired products. In the case of the synthesis of manganese nitride nanoparticles (MnN0,43), nanoparticles with a core-shell structure are obtained, their use as conversion materials in batteries is first introduced. On the other hand, the formation of zirconium oxynitride nanoparticles (Zr2ON2) can be easily influenced by varying the reaction conditions such as the amount of urea or the reaction temperature. The addition of small amounts of salt prevents the formation of carbon in the final product, leading to yellow Zr2ON2 nanoparticles with a size of d = 8 nm which show semiconductor behavior.

Deposition of solid state materials span a wide variety of methods and often utilize high energy sources such as plasmas and ultra-violet light resulting in a wide variety of characteristics and applications. A fundamental understanding is essential for furthering the applications of these materials which include catalysis, molecular filtration, electronics, sensing devices, and energy storage among others. A combination of experimental and theoretical work is presented here on several materials including 2D silicates on Pd, boron oxide, and vanadium oxynitride. Silicate formation under low energy electron microscopy demonstrate film permeability to oxygen, while ab initio molecular dynamics simulations reveal the possible initial mechanisms associated with the formation of boron oxide films during atomic layer deposition. Lastly, vanadium oxynitrides have shown preferential sputtering of N over O sites and theoretical binding energies serve as a guide for assigning experimental x-ray photoelectron spectra.