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International audience; Mg 3 (BH 4) 4 (NH 2) 2 compound was synthesized through the investigation of the Mg(BH 4) 2-Mg(NH 2) 2 phase diagram; its crystal structure was solved in a tetragonal unit cell with the space group I4̅. Interestingly, Mg 3 (BH 4) 4 (NH 2) 2 has a high thermal stability with a decomposition temperature above 190°C and exhibits a high Mg 2+ ionic conductivity of 4.1 × 10 −5 S•cm −1 at 100°C with a low activation energy (0.84 eV). The reversible Mg deposition/stripping was demonstrated at 100°C when using Mg 3 (BH 4) 4 (NH 2) 2 as solid electrolyte. Thus, Mg 3 (BH 4) 4 (NH 2) 2 is a compound that could help to develop rechargeable Mg-ion solid-state batteries.

Structural changes produced by irradiation have been extensively studied in compounds derived from the parent fluorite structure where cations are initially ordered and in systems where both sub-lattices do not display long-range order. The irradiation behaviour of fluorite-related oxide systems where the cations are randomly distributed but the anions are highly ordered is not quantitatively explored yet. We report on a model system Gd2Ce2O7, with a randomly occupied cation sub-lattice while an ordered anion sublattice. This compound crystallizes in a new bixbyite-type symmetry where O vacancies order on half of the vacant sites of the ideal bixbyite structure. Swift heavy ion irradiation experiments and quantitative x-ray diffraction analysis were used to study the separate response of the anion sub-lattice to radiation. We show that the topological disorder on the anion sub-lattice grows faster than that on the cation sub-lattice. While a decrease in strain is observed as a function of fluence, the variance of the strain increases due to an increase of the microdomain wall density.

The current global interest in energy storage has triggered the development of new composite materials and, consequently, new methodologies for manufacturing and testing these products. In the energy storage research field their mechanical behavior is less investigated, despite of their high both fundamental and technological relevance. To assess the interplay between charge and mass transport, this thesis focusses on a large variety of electrolytes using shear rheology and dielectric spectroscopy as examination methods. Tailoring the mechanical behavior of these materials, this work investigates the impact of their local and macroscopic viscoelasticity on their conductivity, with the ultimate goal of finding new recipes for improving the latter. Our investigations from a series of mixtures with an ionic liquid and a dipolar one shows an unusual shifting in the coupling between the mechanical and conductvity processes. A survey of ionogels demonstrate that the interaction of charge carriers with their gel-like matrix can affect conductivity even in the presence of a strong dynamical disparity between its macroscopic mechanical and electrical parameters. Finally, comparing ionic and proton conductors, it is shown that this decoupling significantly enhances the conductivity in acid hydrates. Our results and their analysis show that enhancing the degree of decoupling between the mechanical and electrical degrees of freedom, combined with a reduction of charge correlations in highly concentrated electrolytes are essential for the development of the next generation of energy storage materials., Das derzeitige weltweite Interesse an der Energiespeicherung hat zur Entwicklung neuer Verbundwerkstoffe und folglich zu neuen Methoden für die Herstellung und Prüfung dieser Produkte geführt. In der Energiespeicherforschung wird das mechanische Verhalten jedoch weniger untersucht, obwohl es sowohl von grundlegender als auch technologischer Bedeutung ist. Um das Zusammenspiel von Ladungs- und Massentransport zu bewerten, konzentriert sich diese Arbeit auf eine Vielzahl von Elektrolyten, wobei Scherrheologie und dielektrische Spektroskopie als Untersuchungsmethoden eingesetzt werden. Indem wir das mechanische Verhalten dieser Materialien anpassen, untersuchen wir den Einfluss ihrer lokalen und makroskopischen Viskoelastizität auf ihre Leitfähigkeit, mit dem Ziel, neue Ansätze zur Verbesserung der Leitfähigkeit zu finden. Unsere Untersuchungen an einer Reihe von Mischungen mit einer ionischen und einer dipolaren Flüssigkeit zeigen eine ungewöhnliche Verschiebung in der Kopplung zwischen mechanischem und Leitfähigkeits-Prozess. Eine Untersuchung von Ionengelen zeigt, dass die Wechselwirkung von Ladungsträgern mit ihrer gelartigen Matrix die Leitfähigkeit auch dann beeinflussen kann, wenn eine starke dynamische Diskrepanz zwischen den makroskopischen mechanischen und elektrischen Parametern besteht. Schließlich wird durch den Vergleich von Ionen- und Protonenleitern gezeigt, dass diese Entkopplung die Leitfähigkeit in Säurehydraten signifikant erhöht. Unsere Ergebnisse und deren Analysen zeigen, dass die Verbesserung des Entkopplungsgrades zwischen den mechanischen und elektrischen Freiheitsgraden in Verbindung mit einer Reduzierung der Ladungskorrelationen in hochkonzentrierten Elektrolyten für die Entwicklung der nächsten Generation von Energiespeichermaterialien von essentieller Bedeutung ist.

Developing high specific energy Lithium-ion (Li-ion) batteries is of vital importance to boost the production of efficient electric vehicles able to meet the customers’ expectation related to the electric range of the vehicle. One possible pathway to high specific energy is to increase the operating voltage of the Li-ion cell. Cathode materials enabling operation above 4.2 V are available. The stability of the positive electrode-electrolyte interface is still the main bottleneck to develop high voltage cells. Moreover, important research efforts are devoted to the substitution of graphite anodes with Li metal: this would improve the energy density of the cell dramatically. The use of metallic lithium is prevented by the dendrite growth during charge, with consequent safety problems. To suppress the formation of dendrites solid-state electrolytes are considered the most promising approach. For these reasons the present review summarizes the most recent research efforts in the field of high voltage solid-state electrolytes for high energy density Li-ion cells.

We present a computational approach for identifying the important descriptors of the ionic conductivities of lithium solid electrolytes. Our approach discriminates the factors of both bulk and grain boundary conductivities, which have been rarely reported. The effects of the interrelated structural (e.g. grain size, phase), material (e.g. Li ratio), chemical (e.g. electronegativity, polarizability) and experimental (e.g. sintering temperature, synthesis method) properties on the bulk and grain boundary conductivities are investigated via machine learning. The data are trained using the bulk and grain boundary conductivities of Li solid conductors at room temperature. The important descriptors are elucidated by their feature importance and predictive performances, as determined by a nonlinear XGBoost algorithm: (i) the experimental descriptors of sintering conditions are significant for both bulk and grain boundary, (ii) the material descriptors of Li site occupancy and Li ratio are the prior descriptors for bulk, (iii) the density and unit cell volume are the prior structural descriptors while the polarizability and electronegativity are the prior chemical descriptors for grain boundary, (iv) the grain size provides physical insights such as the thermodynamic condition and should be considered for determining grain boundary conductance in solid polycrystalline ionic conductors., GRAPHICAL ABSTRACT

La2Mo2O9 based Tb-doped compound, La2-xTbxMo2O9 (x=0.1, 0.2, 0.5), was synthesized and characterised by EIS studies. The frequency and temperature dependent dielectric, electric modulus and ac conductivity studies have been done. Different formalisms have been used to understand relaxation mechanism in our compound. The conductivity in these specimens appears to be due to mobility of oxygen ions.

The formation phenomena of silver carbonate (Ag2CO3)–silver iodide (AgI) solid solutions were investigated by X-ray diffraction, thermogravimetry-differential thermal analysis, and electrical conductivity measurement. Results revealed that AgI and Ag2CO3 reacted with each other when mixed at room temperature. The reaction products were classified into three types: (1) AgI-based solid solutions in the AgI-rich region for x = 10% or less in x Ag2CO3–(1 − x) AgI; (2) Ag2CO3-based solid solutions in the Ag2CO3-rich region for x = 60% or more; and (3) silver carbonate iodides in the intermediate range for x between 10% and 60%. For the AgI-based solid solutions, the incorporation of Ag2CO3 into the AgI lattice expanded the unit cell and enhanced electrical conductivity. The solubility limit of Ag2CO3 into the AgI lattice estimated from the differential thermal analysis was x ≈ 5%.

The organic–inorganic hybrid non-centrosymmetric material [(C 2 H 5 ) 4 N] 2 ZnI 3.86 Cl 0.14 has been studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), dielectric and transport measurements. In analogy with the corresponding tetraiodo-zincate analogue, the material crystallizes at room temperature in the tetragonal system, space group P 4 2 1 m (No. 113), with lattice parameters a = 13.743(6) and c = 14.785(10) A. DSC and XRD characterizations pointed out the occurrence of two phases transitions, one of second order at about 290 K and the other of the first order at T = 451 K. The former is related to an electrical transition from insulating to thermally activated transport mechanism displaying clear hints of ionic conduction, the latter leads to a phase showing the typical features of plastic crystals in its powder XRD pattern. The pattern was indexed by an orthorhombic cell, a = 15.724(1), b = 17.907(1) and c = 10.585(1) A, and a reliable model was found and refined in the Pna2 1 space group. The model consists of ordered tetrahedral ZnCl 4 2− units intercalated by fully disordered tetraethylammonium cations.

Solid Oxide Fuel Cells (SOFCs) are a promising technology that can provide efficient and clean energy production. The general barriers hindering their market entry are durability, i.e. resistance to aging, and costs. In parallel to the deeper insight into the different degradation sources and improved understanding of ageing factors and their interactions, work towards higher accuracy for the assessment and monitoring of real-world fuel cell ageing in necessary. The requirements for operational stability formulate the parameter “degradation rate” (DR). Most often long term durability tests are performed at constant current load and the decrease of the voltage is used for its definition. In this work a new approach based on analysis of the volt-ampere characteristics, named Differential Resistance Analysis (DRA), is presented. It operates with the differential resistance, i.e. with the derivative of the voltage in respect to the current (dU/dI = Rd) which is more sensitive to small deviations and thus increases the sensitivity of the analysis. Two performance indicators are derived (Rd, min and ∆U*) with differing selectivity: ∆U* is more sensitive to activation losses and Rd, min - to transport hindrances. The application of the DRA is demonstrated on examples from measurements in fuel cell and in reverse (fuel cell/electrolyzer) mode, as well as on modeling data. The results show that the method is at least 10 times more sensitive to DR evaluation in comparison with the classical approach.

In this work, a new type of addition reaction between La(BH4)3 and LiX, X = Cl, Br, I, is used to synthesize LiLa(BH4)3Cl and two new compounds LiLa(BH4)3X, X = Br, I. This method increases the amounts of LiLa(BH4)3X and the sample purity. The highest Li-ion conductivity is observed for LiLa(BH4)3Br, 7.74 × 10-5 S/cm at room temperature (RT) and 1.8 × 10-3 S/cm at 140°C with an activation energy of 0.272 eV. Topological analysis suggests a new lithium ion conduction pathway with two new different types of bottleneck windows. The sizes of these windows reveal an opposite size change with increasing lattice parameter, that is, increasing size of the halide ion in the structure. Thus, we conclude that the sizes of both windows are important for the lithium ion conduction in LiLa(BH4)3X compounds. The lithium ion conductivity is measured over one to three heating cycles and with different contacts (gold or carbon) between the electrodes and the electrolyte. Moreover, 11B MAS NMR is used to verify the contents of the samples, whereas thermogravimetric analysis shows 4.8 and 3.6 wt % of hydrogen release for LiLa(BH4)3Cl and LiLa(BH4)3Br in the temperature range RT to 400°C. (Graph Presented).

The 70-year history of scientific endeavor of solid state ionics research in Japan is reviewed to show the contribution of Japanese scientists to the basic science of solid state ionics and its applications. The term ‘solid state ionics’ was defined by Takehiko Takahashi of Nagoya University, Japan: it refers to ions in solids, especially solids that exhibit high ionic conductivity at a fairly low temperature below their melting points. During the last few decades of exploration, many ion conducting solids have been discovered in Japan such as the copper-ion conductor Rb4Cu16I7Cl13, proton conductor SrCe1–xYxO3, oxide-ion conductor La0.9Sr0.9Ga0.9Mg0.1O3, and lithium-ion conductor Li10GeP2S12. Rb4Cu16I7Cl13 has a conductivity of 0.33 S cm–1 at 25 °C, which is the highest of all room temperature ion conductive solid electrolytes reported to date, and Li10GeP2S12 has a conductivity of 0.012 S cm–1 at 25 °C, which is the highest among lithium-ion conductors reported to date. Research on high-temperature proton conducting ceramics began in Japan. The history, the discovery of novel ionic conductors and the story behind them are summarized along with basic science and technology.

This thesis is focused on the understanding and development of novel materials for valence-change memories (VCMs), a type of resistive switching memories in which the memory storage mechanism is based on internal redox reactions. VCMs are in essence electrochemical systems. Their implementation in integrated electronic circuits relies on a voltage (or current) to measure and operate the memory, but their functionality is highly dependent on the chemical properties of the materials constituting the memory. In this work we present how the mixed ionic-electronic conducting La2NiO4+δ compound offers an interesting playground for VCM applications due to its intrinsic bulk oxygen-ion conducting properties. We have successfully prepared La2NiO4+δ in the form of highly oriented thin films on SrTiO3 single crystal substrates using pulsed-injection chemical vapour deposition (PiMOCVD). Post-annealing treatments in oxidizing/reducing atmospheres allow tuning the oxygen content and the p-type semiconducting properties of La2NiO4+δ due to a self-doping mechanism. The obtained oxygen over-stoichiometry in the 0 ≤ δ ≤ 0.08 range induced a variation of the film resistivity between 5.7 Ω.cm and 5.3x10-3 Ω.cm for hydrogen or oxygen-annealed samples, respectively. The optimized La2NiO4+δ thin films have been used as a base for the microfabrication of metal/La2NiO4+δ/metal heterostructures. The important role of the metal/oxide junction in interface-type VCMs is discussed in detail. In particular, an ohmic contact is obtained with La2NiO4+δ when using a high work function metal such as Pt, while rectifying contact properties are obtained when using Ti due to the presence of a spontaneously-formed TiOx interlayer (~8 nm) at the Ti/L2NO4 interface. An asymmetric Pt/La2NiO4+δ/Ti heterojunction has been selected as a first prototype to assess the memory capabilities of a La2NiO4+δ-based memristive device. A continuous bipolar analogue-type memory behaviour has been measured, together with strong multilevel programing capabilities when operated in pulsed mode. In addition, the promising results offered by this prototypical device have been extended for the first time to La2NiO4+δ/LaNiO3 bilayers, showing memory relaxation properties, which are potentially interesting for short-term memory and filtering applications in neuromorphic-based computational hardware., Cette thèse porte sur la compréhension et le développement de matériaux innovants en tant que composant actif pour les mémoires résistives à changement de valence (VCM), qui constitue une sous-catégorie des mémoires résistives où des réactions d’oxydoréduction sont à l’origine du mécanisme de commutation résistive. Leur incorporation dans les circuits intégrés nécessite une tension (ou un courant) électrique pour lire et programmer la mémoire, cependant leurs fonctionnalités dépend essentiellement des propriétés chimiques des matériaux constituant la mémoire. Dans ce manuscrit nous étudions les propriétés du composé La2NiO4+δ, un conducteur mixte d’ions et d’électrons qui de par sa conduction d’ions oxydes dans le volume du matériau offre un terrain de jeu prometteur pour les VCMs. Nous avons pu obtenir des films minces de La2NiO4+δ fortement texturés sur des substrats monocristallins de SrTiO3 par dépôt chimique en phase vapeur à partir de l’injection pulsée de précurseurs métalorganiques (PiMOCVD). Des recuits sous atmosphère contrôlée ont permis de faire varier le contenu en oxygène et d’ajuster les propriétés semiconductrices-type p de La2NiO4+δ par un mécanisme d’auto-dopage. Une sur-stœchiométrie en oxygène dans la plage 0 ≤ δ ≤ 0.08 induit une variation de résistivité de 5.7 Ω.cm à 5.3x10-3 Ω.cm pour un recuit sous hydrogène ou sous oxygène, respectivement. Les films minces de La2NiO4+δ ont ensuite été utilisés comme base dans la conception d’hétérostructures métal/La2NiO4+δ/métal. Le rôle important de la jonction métal/oxyde sur les propriétés des VCMs de type interfaciales est discuté en détails. En particulier, un contact ohmique avec La2NiO4+δ est obtenu en utilisant un matériau d’électrode tel que le Pt ayant un travail de sortie élevé, alors qu’un contact rectifiant est obtenu avec Ti résultant de la présence d’une fine couche (~8 nm) de TiOx formée de manière spontanée à l’interface Ti/La2NiO4+δ. Une hétérojunction asymétrique Pt/La2NiO4+δ/Ti a été sélectionnée comme prototype afin d’évaluer les propriétés memristives de composants basés sur La2NiO4+δ. Un changement de résistance bipolaire a été mesuré ainsi qu’une possibilité de programmation largement multi-niveaux lorsque la mémoire est stimulée de manière pulsée. Les résultats prometteurs obtenus par ce premier prototype sont ensuite étendus pour la première fois à un système plus complexe de bicouches La2NiO4+δ/LaNiO3. Des propriétés de relaxation ont été mesurées, rendant ces mémoires intéressantes pour leur utilisation en tant que mémoire volatile pour un filtrage dynamique dans des applications neuromorphiques.

This thesis is focused on the understanding and development of novel materials for valence-change memories (VCMs), a type of resistive switching memories in which the memory storage mechanism is based on internal redox reactions. VCMs are in essence electrochemical systems. Their implementation in integrated electronic circuits relies on a voltage (or current) to measure and operate the memory, but their functionality is highly dependent on the chemical properties of the materials constituting the memory. In this work we present how the mixed ionic-electronic conducting La2NiO4+δ compound offers an interesting playground for VCM applications due to its intrinsic bulk oxygen-ion conducting properties. We have successfully prepared La2NiO4+δ in the form of highly oriented thin films on SrTiO3 single crystal substrates using pulsed-injection chemical vapour deposition (PiMOCVD). Post-annealing treatments in oxidizing/reducing atmospheres allow tuning the oxygen content and the p-type semiconducting properties of La2NiO4+δ due to a self-doping mechanism. The obtained oxygen over-stoichiometry in the 0 ≤ δ ≤ 0.08 range induced a variation of the film resistivity between 5.7 Ω.cm and 5.3x10-3 Ω.cm for hydrogen or oxygen-annealed samples, respectively. The optimized La2NiO4+δ thin films have been used as a base for the microfabrication of metal/La2NiO4+δ/metal heterostructures. The important role of the metal/oxide junction in interface-type VCMs is discussed in detail. In particular, an ohmic contact is obtained with La2NiO4+δ when using a high work function metal such as Pt, while rectifying contact properties are obtained when using Ti due to the presence of a spontaneously-formed TiOx interlayer (~8 nm) at the Ti/L2NO4 interface. An asymmetric Pt/La2NiO4+δ/Ti heterojunction has been selected as a first prototype to assess the memory capabilities of a La2NiO4+δ-based memristive device. A continuous bipolar analogue-type memory behaviour has been measured, together with strong multilevel programing capabilities when operated in pulsed mode. In addition, the promising results offered by this prototypical device have been extended for the first time to La2NiO4+δ/LaNiO3 bilayers, showing memory relaxation properties, which are potentially interesting for short-term memory and filtering applications in neuromorphic-based computational hardware.; Cette thèse porte sur la compréhension et le développement de matériaux innovants en tant que composant actif pour les mémoires résistives à changement de valence (VCM), qui constitue une sous-catégorie des mémoires résistives où des réactions d’oxydoréduction sont à l’origine du mécanisme de commutation résistive. Leur incorporation dans les circuits intégrés nécessite une tension (ou un courant) électrique pour lire et programmer la mémoire, cependant leurs fonctionnalités dépend essentiellement des propriétés chimiques des matériaux constituant la mémoire. Dans ce manuscrit nous étudions les propriétés du composé La2NiO4+δ, un conducteur mixte d’ions et d’électrons qui de par sa conduction d’ions oxydes dans le volume du matériau offre un terrain de jeu prometteur pour les VCMs. Nous avons pu obtenir des films minces de La2NiO4+δ fortement texturés sur des substrats monocristallins de SrTiO3 par dépôt chimique en phase vapeur à partir de l’injection pulsée de précurseurs métalorganiques (PiMOCVD). Des recuits sous atmosphère contrôlée ont permis de faire varier le contenu en oxygène et d’ajuster les propriétés semiconductrices-type p de La2NiO4+δ par un mécanisme d’auto-dopage. Une sur-stœchiométrie en oxygène dans la plage 0 ≤ δ ≤ 0.08 induit une variation de résistivité de 5.7 Ω.cm à 5.3x10-3 Ω.cm pour un recuit sous hydrogène ou sous oxygène, respectivement. Les films minces de La2NiO4+δ ont ensuite été utilisés comme base dans la conception d’hétérostructures métal/La2NiO4+δ/métal. Le rôle important de la jonction métal/oxyde sur les propriétés des VCMs de type interfaciales est discuté en détails. En particulier, un contact ohmique avec La2NiO4+δ est obtenu en utilisant un matériau d’électrode tel que le Pt ayant un travail de sortie élevé, alors qu’un contact rectifiant est obtenu avec Ti résultant de la présence d’une fine couche (~8 nm) de TiOx formée de manière spontanée à l’interface Ti/La2NiO4+δ. Une hétérojunction asymétrique Pt/La2NiO4+δ/Ti a été sélectionnée comme prototype afin d’évaluer les propriétés memristives de composants basés sur La2NiO4+δ. Un changement de résistance bipolaire a été mesuré ainsi qu’une possibilité de programmation largement multi-niveaux lorsque la mémoire est stimulée de manière pulsée. Les résultats prometteurs obtenus par ce premier prototype sont ensuite étendus pour la première fois à un système plus complexe de bicouches La2NiO4+δ/LaNiO3. Des propriétés de relaxation ont été mesurées, rendant ces mémoires intéressantes pour leur utilisation en tant que mémoire volatile pour un filtrage dynamique dans des applications neuromorphiques.

Solid inorganic and polymeric electrolytes have the potential to enable rechargeable batteries with higher energy densities, compared to current lithium-ion technology, which uses liquid electrolyte. Inorganic materials such as ceramics and glasses conduct lithium ions well, but they are brittle, which makes incorporation into a battery difficult. Polymers have the flexibility for facile use in a battery, but their transport properties tend to be inferior to inorganics. Thus, there is growing interest in composite electrolytes with inorganic and organic phases in intimate contact. This article begins with a discussion of ion transport in single-phase electrolytes. A dimensionless number (the Newman number) is presented for quantifying the efficacy of electrolytes. An effective medium framework for predicting transport properties of composite electrolytes containing only one conducting phase is then presented. The opportunities and challenges presented by composite electrolytes containing two conducting phases are addressed. Finally, the importance and status of reaction kinetics at the interfaces between solid electrolytes and electrodes are covered, using a lithium-metal electrode as an example.

As an ionic conductive functional layer of intermediate temperature solid oxide fuel cells (ITSOFC), samarium-doped ceria (SDC)–LiNaSO4 nano-composites were synthesized by a sol–gel method and their properties were investigated. It was found that the content of LiNaSO4 strongly affected the crystal phase, defect concentration, and conductivity of the composites. When the content of LiNaSO4 was 20 wt%, the highest conductivity of the composite was found to be, respectively, 0.22, 0.26, and 0.35 S cm−1 at temperatures of 550, 600, and 700 °C, which are much higher than those of SDC. The peak power density of the single cell using this composite as an interlayer was improved to, respectively, 0.23, 0.39, and 0.88 W cm−2 at 500, 600, and 700 °C comparing with that of the SDC-based cell. Further, the SDC–LiNaSO4(20 wt%)-based cell also displayed better thermal stability according to the performance measurements at 560 °C for 50 h. These results reveal that SDC–LiNaSO4 composite may be a potential good candidate as interlayer for ITSOFC due to its high ionic conductivity and thermal stability.

[EN] Increased availability of methane from shale gas and stranded gas deposits in the recent years may facilitate the production of ethylene by means of potentially more competitive routes than the state-of-the-art steam cracking processes. One appealing route is the oxidative coupling of methane (OCM), which is considered in this work for the production of ethylene by means of the use of catalytic membrane reactors (CMR) based on Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) ceramic material. In a first approach, a screening of 15 formulations as catalysts for the ethylene-ethane production was conducted on CMR consisting of disk-shaped planar BSCF membranes. At 900 degrees C, the maximum C-2 selectivity was 70%, reached with Ba0.5Sr0.5FeO3-delta and La0.5Ce0.1Sr0.4Co0.8Fe0.2O3-delta catalysts. On the other hand, low CH4 conversions (X-CH4) resulted in C-2 yields below 3%. Operation at 1,000 degrees C significantly shifted X-CH4 for all the activated membranes due to the decrease in CH4/O-2 ratios, thus obtaining C-2 yields close to 9% and productivities of ca. 1.2ml.min(-1).cm(-2) with Ce0.9Gd0.1O2-delta and Ba0.5Sr0.5Co0.8Fe0.2O3-delta impregnated with Mn-Na2WO4 catalysts. The performance of OCM reaction was also studied in a tubular catalytic membrane reactor. Tubular configuration improved C-2 yield by minimizing CH4/O-2 ratios up to 1.7, obtaining a maximum of 15.6% at 900 degrees C with a BSCF capillary membrane activated with a packed bed of 2 wt% Mn/5 wt% Na2WO4 on SiO2 catalyst., Financial support by the Spanish Government (ENE2014-57651 and SEV-2012-0267 grants) and by the EU through FP7 GREEN-CC Project (GA 608524), is gratefully acknowledged. The authors want also acknowledge the Electron Microscopy Service from the Universitat Politecnica de Valencia for their support in the SEM analysis performed in this work.

The viability of water gas shift catalytic system for mobile application passes through obligatory reactor volume reduction, achieved normally by using less charge of more efficient catalyst. Completely new concept for catalyst design is proposed: a catalytic system including classically reported WGS catalysts of different nature or active phase (Cu, Pt or Au) mechanically mixed with an ionic conductor. The influence of the later on catalyst activity is studied and discussed, more precisely its effect on the rate of the reaction-limiting step and catalysts’ efficiency. It is demonstrated with this study, that the presence of an ionic conductor in contact with a WGS catalyst is essential for the water supply (dissociation and transport), thereby potentiating the water activation step, whatever the mechanism and catalyst overall performance., We acknowledge financial support for this work from the Spanish Ministerio de Economía y Competitividad (MINECO) (ENE2015-66975-C3-2-R).

To develop high performance solid ionic conductors, various kinds of compounds and solid solutions have been prepared and the relations between their crystal structures and conductivities have been studied. Here, the prospect and development of the solid ionic conductors were mentioned especially focusing on the 38 year’s results by the present author’s laboratory together with the innovative experimental methods.

LaW x Nb 1−x O 4+x/2 ceramics (x = 0.16) were prepared via a solid state route and studied with respect to phase stability and mixed ionic and electronic conductivity under conditions of technological relevance for fuel cell applications. The chemical compatibility against standard cathode materials revealed that Sr-doped LaMnO 3 could be used without detectable chemical interaction up to at least 1000 °C. Impedance spectroscopy measurements performed in the range 400–850 °C, using different atmospheres (air and N 2 +H 2 , both dry and water vapour saturated), suggest oxygen transport numbers equal to 1 under oxidising conditions, and decreasing when exposed to extreme reducing conditions. The total conductivity at 800 °C increases from 1.4·10 −3 S cm −1 in air to 2.5·10 −3 S cm −1 in wet hydrogen and 6.1·10 −3 S cm −1 in dry hydrogen, but the observed onset of n-type conductivity has little practical impact under typical fuel cell operating conditions.

This work reports on the investigation of CO 2 selective membranes for pre-combustion and post- combustion processes, in which CO 2 is extracted from multi-component gas streams at intermediate temperature (400 – 600 °C). The dual-phase membranes developed in this work are designed as a porous oxide ion conducting ceramic matrix, which is infiltrated with a molten carbonate phase. Both ex-situ and in-situ characterization methods were used to study disk shaped and tubular membranes. The gas transport properties of disk-shaped membranes were further investigated under various operating conditions relevant for both post-combustion and pre-combustion applications.

Lithium superionic conductors with the Li10GeP2S12 (LGPS)-type structure are promising materials for use as solid electrolytes in next-generation lithium batteries. A novel member of the LGPS family, Li9.42Si1.02P2.1S9.96O2.04, and its solid solutions were synthesised by quenching from 1273 K in the Li2S–P2S5–SiO2 pseudoternary system. The material exhibited an ionic conductivity as high as 3.2×10−4 S cm−1 at 298 K, as well as the high electrochemical stability to lithium metal, which was improved by the introduction of oxygen into the LGPS-type structure. An all-solid-state cell with a lithium metal anode and Li9.42Si1.02P2.1S9.96O2.04 as the separator showed excellent performance with a high coulomb efficiency of 100%. Thus, oxygen doping is an effective way of improving the electrochemical stability of LGPS-type structure.

In order to investigate why crystal symmetry lowers with increasing temperature by phase transition of TII–III (=369 K) in Cs3H(SeO4)2, in spite of the fact that crystal symmetry in the high-temperature phase of many ionic conductors becomes higher by the phase transition, we have studied the relation between the change in crystal symmetry and the appearance of proton motion. It was found from the analysis of domains based on crystal structure that the number of possible geometrical arrangement of hydrogen bond in phase II becomes two times larger than that in phase III, derived from the lowering of crystal symmetry with increasing temperature. These results indicate that the lowering of crystal symmetry in phase II appears by the increase of the number of geometrical arrangements and by the enhancement of the flexibility of hydrogen bond. Considering that the enhancement of the flexibility of hydrogen bond yields mobile proton in phase II, it is deduced that mobile proton in phase II appears in exchange for the lowering of crystal symmetry at II–III phase transition.

Rapidly growing attention is being recently directed towards the investigation of the ionic conducting properties of oxide film hetero-structures. Experimental evidence has been reported showing that interfacial phenomena at hetero-phase interfaces give rise to faster ion conduction pathways than the bulk or homo-phase interfaces. Nonetheless, a deeper understanding of the interface transport properties is still needed to exploit these effects. In this work we have investigated the growth mechanism of different superlattices fabricated by pulsed laser deposition (PLD) coupling doped and undoped cerium and zirconium oxides. Single crystalline MgO wafers were selected as deposition substrates. The superlattice structures were obtained by means of a thin buffer layer of SrTiO3 (STO). The growth mechanism was investigated by reflection high energy electron diffraction (RHEED) and X-ray diffraction (XRD) analyses.

Ionic liquid (IL) based gel polymer electrolytes (GPEs) are being investigated extensively at present as substitutes for conventional GPEs based on a polymer, a salt and solvents. The main reason behind this is the drawbacks in usage of solvents. IL based GPEs have been employed for energy storage devices such as batteries and super capacitors due to their interesting mechanical, physical and electrochemical properties. This study focused on synthesis preparation and characterization of an IL based GPE consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-co-HFP), zinc trifluoro metha -nesulfonate (Zn(CF3SO3)2 - ZnTF) and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (1E3MITF). Thin film samples were prepared using solvent casting method. The optimized composition was found to be 1 PVdF-co-HFP: 1 1E3MITF: 3 ZnTF (by weight basis). This mechanically stable, thin film has the maximum room temperature conductivity of 7.42×10-3 S cm-1. Conductivity variation with temperature follows Vogel - Tamman - Fulcher (VTF) behavior confirming the relation of conductivity mechanism with the free volume theory. The IL based GPE is a purely an ionic conductor having a considerable anionic contribution. It shows stability up to 2.5 V which is very much convenient from a practical point of view. Oxidation and reduction of Zn takes place at the potentials of 0.5 V and –0.5 V, respectively. In addition, Zn platting and stripping occurs only on the Zn electrodes but not on the stainless steel (SS) electrodes. Impedance measurements taken for the GPE continuously for a long period of time exhibited a satisfactory stability with Zn electrodes.

We present electrical conductivity measurements of BIFEVOX Bi4V2-xFexO11-y (0≤x≤0.9; 0≤y≤1), in which V (IV) ions have been systematically substituted by Fe (III) ions. Conductivity shows a power law frequency dependence described by the form σ*(ω)=σdc[1+(jω/ωp)n], known as universal dynamic response. Conversely, the electric modulus shows asymmetric peaks, characterized by stretched exponentials relaxation functions in time domain of the form φ(t)=exp(-(t/τσ)β). β is determined by the degree of correlation in the ionic motion. It´s value, β=0.56±0.03, is almost independent of temperature and iron content. Increasing Fe content leads to an exponential decrease of the conductivity and to an increase of the activation energy of the conduction process from 0.20 to 0.97 eV. These results are discussed in terms of oxygen vacancy ordering upon Fe (III) substitution.Presentamos medidas de la conductividad eléctrica del sistema BIFEVOX Bi4V2-xFexO11-y (0≤x≤0.9; 0≤y≤1), en el que se realiza la sustitución de iones V (IV) por Fe (III) de forma sistemática. La conductividad muestra un comportamiento potencial con la frecuencia, descrito por σ*(ω)=σdc[1+(jω/ωp)n], y conocido como respuesta dieléctrica universal. Análogamente, el módulo eléctrico presenta picos asimétricos, cuya función de relajación en el dominio del tiempo puede describirse mediante exponenciales “estiradas” de la forma φ(t)=exp(-(t/τσ)β). β da cuenta del grado de correlación del transporte iónico, siendo su valor, β=0.56±0.03, casi independiente de la temperatura y del contenido en Fe. Con el aumento en el contenido de Fe, la conductividad disminuye exponencialmente y la energía de activación del proceso de conducción aumenta de 0.20 a 0.97 eV. Estos resultados se discuten en términos de la ordenación de vacantes oxígeno al dopar con Fe (III).

The single component fuel cell (SCFC) is a novel physical-electrochemical device for energy conversion which is recently discovered. The functional composite materials of Li0.15Ni0.25Cu0.3Zn0.3O2-delta (LNCZO) and Ce0.8Sm0.2O1.9 (SDC)-carbonate are proved as unique materials in SCFC (or one-layer fuel cell). In this work, the microstructure and morphology of two composite materials of LNCZO-SDC-Na2CO3 (LNCZO-NSDC) and LNCZO-SDC-(Li/ Na)(2)CO3 (LNCZO-LNSDC) are investigated by SEM-EDX and HR-TEM. Their catalytic activities for both hydrogen oxidation and oxygen reduction are studied by H-2-TPR and O-2-TPD, respectively. It is discovered for the first time that binary carbonates as ionic conductor mixing with semiconductor homogenously help to form unique semiconducting-ionic microstructure. The particle arrangement and interface conduction in the microstructure significantly influences on the SCFC performances due to different catalytic activity and polarization resistance. Even this, O-2 reduction reaction (ORR) for the single homogeneous layer still predominates in the redox reaction and binary carbonates are in favor of the oxygen conduction and desorption. These fin dings are essential to exactly understand the connections among structure, catalytic activities and performances underlying SCFC. QC 20150109

Solid oxide fuel cells (SOFCs) offer an efficient energy conversion technology for alleviating current energy problems. High temperature proton-conducting (HTPC) oxides are promising electrolytes for this technology, since their activation energy is lower than that of conventional oxygen-ion conductors, enabling the operating temperature reduction at 600 °C. Among HTPC oxides, doped BaZrO3 materials possess high chemical stability, needed for practical applications. Though, poor sinterability and the resulting large volume of highly resistive grain boundaries hindered their deployment for many years. Nonetheless, the recently demonstrated high proton conductivity of the bulk revived the attention on doped BaZrO3, stimulating research on solving the sintering issues. The proper selection of dopants and sintering aids was demonstrated to be successful for improving the BaZrO3 electrolyte sinterability. We here briefly review the synthesis strategies proposed for preparing BaZrO3-based nanostructured powders for electrolyte and electrodes, with the aim to improve the SOFC performance.

This study aims to develop a new family of catalysts for diesel soot combustion to produce and optimize self-DPFs, based on ionic conducting ceramics, able to continuously burn soot particulates at low temperatures without fuel overconsumption and without the use of noble metals. The investigated catalysts are oxygen ionically conducting ceramics. Yttria stabilized Zirconia (8-YSZ containing 8 mol% of yttria) was chosen as the reference catalyst due to its high thermal and chemical stability and good ionic conductivity. A set of experiments was implemented to vary different parameters that can influence the reactivity of the reference catalyst. All of these studies have resulted in several major conclusions. Oxygen species active to oxidize soot particles at low temperature are those contained in the catalyst. An electrochemical type mechanism as in a fuel cell but at the nanoscale was proposed: the soot oxidation represents the anodic reaction which occurs at the contact points soot / 8-YSZ/O2 (gas) electrons are diffused through soot particles to triple points between the soot particles (electronic conductor), the gas phase (presence of oxygen) and 8-YSZ (ion conductor) where the cathodic reaction takes place with the incorporation of gaseous oxygen into the ceramic. The key parameters that influence the catalytic activity of 8-YSZ are soot / catalyst contact and thus the agglomerates size of the catalyst powder, the oxygen partial pressure in the gas phase and the mobility of oxygen in the catalyst, Cette étude a pour finalité le développement d'une nouvelle famille de catalyseurs pour la combustion des suies Diesel afin de produire des filtres à particules (FAP) à régénération continue basse température. En effet, les régénérations périodiques des FAP actuellement commercialisés, engendrent une surconsommation plus ou moins élevée en carburant. Les catalyseurs étudiés sont des céramiques conductrices par les ions oxygènes et exempts de métal noble. L'ensemble de ces études a permis d'aboutir à plusieurs conclusions majeures. Les oxygènes actifs pour oxyder les particules de suies à basse température sont les oxygènes contenus dans le catalyseur. L'oxydation de la suie a donc lieu à l'interface solide/solide : suie/catalyseur. Un mécanisme de type électrochimique comme dans une pile à combustible mais à l'échelle nanométrique a été proposé : l'oxydation de la suie représente la réaction anodique qui se déroule aux points de contact suie / 8-YSZ, les électrons produits diffusent à travers les particules de suie vers les point triples entre les particules de suie (conductrices électroniques), la phase gaz (présence d'oxygène) et 8-YSZ (conducteur ionique) où se déroule la réaction cathodique d'incorporation de l'oxygène gazeux dans le matériau. Les paramètres clés qui gouvernent l'activité catalytique sont la surface de contact suie/catalyseur et donc la granulométrie de la poudre de catalyseur ainsi que la pression partielle d'oxygène dans la phase gaz et la mobilité de l'oxygène dans le catalyseur

214 σ., Οι πυριτικές ενώσεις λανθανίου, με δομή απατίτη και γενικό τύπο La9.33+xSi6O26+1.5x είναι μία νέα κατηγορία υλικών με ιοντική αγωγιμότητα που πρωτοεμφανίστηκε το 1995. Οι ενώσεις αυτές χαρακτηρίζονται από χαμηλή ενέργεια ενεργοποίησης και εξαιρετική σταθερότητα σε ένα μεγάλο εύρος μερικών πιέσεων Ο2, επομένως είναι κατάλληλες για διάφορες ηλεκτροχημικές εφαρμογές. Η δομή των ενώσεων αυτών επιτρέπει ένα μεγάλο εύρος υποκατάστασης των La/Si και μη-στοιχειομετρίας (οπές κατιόντων ή/και περίσσεια οξυγόνου) που μεταβάλουν σημαντικά την ιοντική τους αγωγιμότητα. Γενικά, οι πυριτικές ενώσεις που παρουσιάζουν υποστοιχειομετρία La ή υπερστοιχειομετρία οξυγόνου εμφανίζουν στην βιβλιογραφία ικανοποιητικές τιμές ιοντικής αγωγιμότητας. Αντικείμενο της παρούσης διατριβής είναι οι ενώσεις πυριτικού Λανθανίου με δομή Απατίτη του τύπου La9.83-x-zSrxSi6-yAlyO26+δ (0x,y,z0.50) και συγκεκριμένα η επιλογή της κατάλληλης μεθόδου σύνθεσης, η επιτυχής σύνθεση αυτών των ενώσεων, η σε βάθος ανάλυση της δομής τους, η μέτρηση των ηλεκτρικών τους ιδιοτήτων και η συσχέτιση στοιχειομετρίας, δομής και ιδιοτήτων. Στα πλαίσια της Διατριβής επιλέχθηκε η τεχνική πολυμερισμού των αρχικών διαλυμάτων (τεχνική Pechini) ως κατάλληλη συνθετική οδός για την παρασκευή των ενώσεων La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5). Η τεχνική Pechini βασίζεται στην ικανότητα του κιτρικού οξέος να σχηματίζει χηλικά σύμπλοκα μετάλλων και την αντίδραση πολυεστεροποίησης ανάμεσα στο κιτρικό οξύ και την αιθυλενογλυκόλη. Οι αντιδράσεις κατά την έψηση μελετήθηκαν με θερμοβαρυμετρική ανάλυση (TGΑ), ενώ για τον χαρακτηρισμό των ενδιάμεσων και τελικών προϊόντων έγιναν μετρήσεις περίθλασης ακτίνων Χ (XRD), υπέρυθρης φασματοσκοπίας (FT-IR) και ηλεκτρονικής μικροσκοπίας σάρωσης (SEM). Στα τελικά προϊόντα έγινε ανάλυση της κρυσταλλικής δομής κατά Rietveld, προσδιορισμός όλων των χαρακτηριστικών μεγεθών (παράμετροι μοναδιαίας κυψελίδας, ατομικές θέσεις, αποστάσεις κλπ.) και απεικόνιση των κρυσταλλικών πλεγμάτων. Τέλος μετρήθηκε η αγωγιμότητα των ενώσεων. Όπως προέκυψε, με την εφαρμογή της τεχνικής πολυμερισμού των αρχικών διαλυμάτων είναι δυνατή η παραλαβή καθαρών ενώσεων La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) ύστερα από έψηση στους 1400οC για 20 h. Πρώτη φορά στη βιβλιογραφία αναφέρεται η παραλαβή καθαρού τελικού προϊόντος για την ένωση La9.83Si6O26+δ, La9.38Sr0.45Si6O26+δ, La9.33Sr0.50Si6O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ και La9.33Sr0.50Si5.70Al0.30O26+δ. Το γεγονός αυτό αυξάνει το εύρος στοιχειομετριών επιτυχούς σύνθεσης για τις ενώσεις πυριτικού Λανθανίου με δομή Απατίτη. Η σύνθεση των ενώσεων με τη μέθοδο του πολυμερισμού των αρχικών διαλυμάτων επηρεάζεται σημαντικά από τις αναλογίες των αρχικών αντιδραστηρίων. Μία μετατροπή του μοριακού λόγου κιτρικό οξύ:μεταλλοκατιόντα από 2 σε 3.3 και μείωση του λόγου διαλύτη:αρχικά αντιδρώντα από 0.21 – 0.28 σε 0.14 οδήγησε σε καθαρά τελικά προϊόντα για τις ενώσεις La9.33Si6O26, La9.68Sr0.15Si5.85Al0.15O26+δ, La9.53Sr0.30Si5.70Al0.30O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ και La9.38Sr0.45Si5.55Al0.45O26+δ ύστερα από έψηση στους 800 οC για 3 h. Είναι η πρώτη φορά που οι ενώσεις La9.68Sr0.15Si5.85Al0.15O26+δ, La9.53Sr0.30Si5.70Al0.30O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ και La9.38Sr0.45Si5.55Al0.45O26+δ παραλαμβάνονται καθαρές σε τόσο χαμηλή θερμοκρασία. Η ανάλυση της δομής κατά Rietveld έδειξε πως οι ενώσεις La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) κρυσταλλώνονται στο εξαγωνικό σύστημα με ομάδα συμμετρίας χώρου την P63/m. Η υποκατάσταση στην θέση του Si έχει σημαντικότερη επίδραση στα μέσα μήκη δεσμών σε σύγκριση με την υποκατάσταση στην θέση του La. Εξετάσθηκε η πιθανότητα ύπαρξης πλεονάζοντος οξυγόνου σε ενδιάμεσες θέσεις του κρυσταλλικού πλέγματος και βρέθηκε πως εντοπίζεται στην περιφέρεια των εξαγωνικών καναλιών που διατρέχουν τη δομή γεγονός που ενισχύει τη θεώρηση για διάχυση ιόντων μέσω μιας ημιτονοειδούς τύπου διαδρομής μέσα από τα εξαγωνικά κανάλια. Η διατομή των προαναφερθέντων καναλιών έχει σημαντική επίδραση στην ιοντική αγωγιμότητα των ενώσεων και συγκεκριμένα μια αύξηση της διατομής ευνοεί τις τιμές αγωγιμότητας. Η υποκατάσταση του La από Sr οδηγεί σε μείωση του μεγέθους των καναλιών ενώ αντίθετη επίδραση έχει η υποκατάσταση του Si από Al. Οι ηλεκτρικές ιδιότητες των ενώσεων πυριτικού Λανθανίου με δομή Απατίτη La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) σχετίζονται σε μεγάλο βαθμό με την διατομή των εξαγωνικών καναλιών οξυγόνου και την ποσότητα πλεονάζοντος οξυγόνου. Η ύπαρξη μιας βέλτιστης αναλογίας μεγέθους καναλιών και ποσότητας οξυγόνου στη δομή των ενώσεων ενισχύει την διάχυση. Σημαντική επίδραση στην αγωγιμότητα έχει η ύπαρξη δευτερευόντων φάσεων καθώς και η πυκνότητα των δειγμάτων. Οι ενώσεις La9.83Si6O26+δ και La9.38Sr0.45Si5.70Al0.30O26+δ εμφανίζουν τις μεγαλύτερες τιμές ιοντικής αγωγιμότητας στους 700 οCμε 11 και 14 mS/cm και τιμές ενέργειας ενεργοποίησης 0.52 και 0.55 eV, αντίστοιχα Οι ενώσεις La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) εμφανίζουν, κυρίως, δύο διαφορετικούς μηχανισμούς ιοντικής αγωγιμότητας. Η διαφοροποίηση αυτή σχετίζεται με την ύπαρξη δύο περιοχών τιμών ενέργειας ενεργοποίησης σε χαμηλές και υψηλές θερμοκρασίες. Ο μηχανισμός στις χαμηλές θερμοκρασίες λειτουργεί μέσω κενών θέσεων οξυγόνου και της περιορισμένης κίνησης του πλεονάζοντος οξυγόνου, το οποίο βρίσκεται παγιδευμένο ενώ σε υψηλές θερμοκρασίες μέσω αποκλειστικά από την μετακίνηση πλεονάζοντος οξυγόνου. Οι ενώσεις La9.33Si6O26, La9.68Sr0.15Si6O26+δ, La9.53Sr0.30Si6O26+δ, La9.68Sr0.15Si5.85Al0.15O26+δ και La9.53Sr0.30Si5.70Al.30O26+δ, δεν ακολούθησαν την παραπάνω συμπεριφορά και εμφάνισαν υψηλές τιμές ενέργειας ενεργοποίησης και χαμηλές τιμές ιοντικής αγωγιμότητας για όλο το εύρος των θερμοκρασιών., Apatite type lanthanum silicates with general formula La9.33+xSi6O26+δ is a newly reported family of compounds which exhibits high ionic conductivity at intermediate temperatures and is considered as promising electrolytes for IT-SOFCs. The structure of these compounds permits a wide range of cation/anion non stoichiometry. It is well established that fully stoichiometric systems e.g. La8Sr2Si6O26 have much lower conductivities and higher activation energies than systems containing either cation vacancies (La9.33Si6O26) or oxygen excess (La9Sr1Si6O26.5). Lately, research groups focus their studies on compounds with both cation vacancies and oxygen excess, in an attempt to further enhance their ionic conductivity. The subject of this thesis has to do with the La9.83-x-zSrxSi6-yAlyO26+δ (0x,y,z0.50) group of compounds and especially with the selection of the most suitable synthetic route, the synthesis of pure final products, the refinement of their crystal structure, the measurement of specific electrical properties and the correlation of the stoichiometry with their structure and properties. All compounds were prepared via a polymeric precursor route where citric acid and ethylene glycol are used as chelating and complexing agents, respectively. Microwave heating is used for the preparation of the precursors and is also tested for their final sintering. The intermediate and final products were examined by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The unit cell, the atomic positions, the length and angle of chemical bonds and the representation of crystal structures were determined by means of Rietveld structure refinement. Finally, ionic conductivity was measured by means of impedance spectroscopy. As it was concluded, pure La9.83-x-zSrxSi6-yAlyO26+δ (0x,y,z0.50) compounds can be prepared through the modified Pechini route after calcination at 1400°C for 20 h. The stoichiometry seems to have a major effect on the structure of the precursors, the dissociation of the polymeric network as well as the structure of final products and the amount of secondary faces.To the best of our knowledge, there is no previous literature on the successful synthesis and detailed structural analysis of La9.83Si6O26+δ, La9.38Sr0.45Si6O26+δ, La9.33Sr0.50Si6O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ and La9.33Sr0.50Si5.70Al0.30O26+δ compound. The synthesis is strongly affected by the ratios of starting materials. A modification of the molar ratio, citric acid to total cations, from 2 to 3.3 as well as a reduction in the molar ratio of solvent to starting materials 0.21 – 0.28 to 0.14 led to the preparation of pure final products for La9.33Si6O26, La9.68Sr0.15Si5.85Al0.15O26+δ, La9.53Sr0.30Si5.70Al0.30O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ and La9.38Sr0.45Si5.55Al0.45O26+δ after calcination at 800°C for 3 h. This is the first time that pure La9.68Sr0.15Si5.85Al0.15O26+δ, La9.53Sr0.30Si5.70Al0.30O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ and La9.38Sr0.45Si5.55Al0.45O26+δ compounds are prepared in such a low temperature. Rietveld analysis showed that La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) compounds crystallize in P63/m space group which owns hexagonal symmetry. The increase in Al doping on Si side exhibits more pronounced effect in the length of chemical bonds in comparison to Sr doping on La side. Moreover, it was concluded that interstitial oxygen accommodates a position at the periphery of the hexagonal channels in the vicinity of the SiO4 groups. This result enforces the theory that ion conduction in apatite lanthanum silicates takes place through a sinusoidal like diffusion of interstitial oxygen. Ion conduction is close related with the size of the hexagonal channels. An enlargement of the hexagonal channels leads in the enhancement of ionic conductivity. It was concluded that an increase in the Sr content reduces the size of the hexagonal channels while an increase in Al content has the opposite effect. The electrical properties of La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) compounds are affected in a major extent by the size of the hexagonal channel as well as the interstitial oxygen content. The existence of an optimum proportion between the size of the hexagonal channels and the interstitial oxygen content enhances the ionic conductivity. The La9.83Si6O26+δ and La9.38Sr0.45Si5.70Al0.30O26+δ compounds exhibit the higher values of ionic conductivity at 700 οC with 11 and 14 mS/cm and activation energy of 0.52 and 0.55 eV, respectively. La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) compounds represent two different ion conduction mechanisms. The low temperature migration mechanism has to do with a combination of diffusion through oxygen vacancy positions and limited diffusion through interstitial oxygen which it remains trapped while the high temperature conduction mechanism is materialized through the motion of the untrapped interstitial oxygen. La9.33Si6O26, La9.68Sr0.15Si6O26+δ, La9.53Sr0.30Si6O26+δ, La9.68Sr0.15Si5.85Al0.15O26+δ and La9.53Sr0.30Si5.70Al.30O26+δ compounds didn’t have the same behavior, exhibiting one mechanism in the whole temperature range which led in low values of conductivity and high values of activation energy.

214 σ., Οι πυριτικές ενώσεις λανθανίου, με δομή απατίτη και γενικό τύπο La9.33+xSi6O26+1.5x είναι μία νέα κατηγορία υλικών με ιοντική αγωγιμότητα που πρωτοεμφανίστηκε το 1995. Οι ενώσεις αυτές χαρακτηρίζονται από χαμηλή ενέργεια ενεργοποίησης και εξαιρετική σταθερότητα σε ένα μεγάλο εύρος μερικών πιέσεων Ο2, επομένως είναι κατάλληλες για διάφορες ηλεκτροχημικές εφαρμογές. Η δομή των ενώσεων αυτών επιτρέπει ένα μεγάλο εύρος υποκατάστασης των La/Si και μη-στοιχειομετρίας (οπές κατιόντων ή/και περίσσεια οξυγόνου) που μεταβάλουν σημαντικά την ιοντική τους αγωγιμότητα. Γενικά, οι πυριτικές ενώσεις που παρουσιάζουν υποστοιχειομετρία La ή υπερστοιχειομετρία οξυγόνου εμφανίζουν στην βιβλιογραφία ικανοποιητικές τιμές ιοντικής αγωγιμότητας. Αντικείμενο της παρούσης διατριβής είναι οι ενώσεις πυριτικού Λανθανίου με δομή Απατίτη του τύπου La9.83-x-zSrxSi6-yAlyO26+δ (0x,y,z0.50) και συγκεκριμένα η επιλογή της κατάλληλης μεθόδου σύνθεσης, η επιτυχής σύνθεση αυτών των ενώσεων, η σε βάθος ανάλυση της δομής τους, η μέτρηση των ηλεκτρικών τους ιδιοτήτων και η συσχέτιση στοιχειομετρίας, δομής και ιδιοτήτων. Στα πλαίσια της Διατριβής επιλέχθηκε η τεχνική πολυμερισμού των αρχικών διαλυμάτων (τεχνική Pechini) ως κατάλληλη συνθετική οδός για την παρασκευή των ενώσεων La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5). Η τεχνική Pechini βασίζεται στην ικανότητα του κιτρικού οξέος να σχηματίζει χηλικά σύμπλοκα μετάλλων και την αντίδραση πολυεστεροποίησης ανάμεσα στο κιτρικό οξύ και την αιθυλενογλυκόλη. Οι αντιδράσεις κατά την έψηση μελετήθηκαν με θερμοβαρυμετρική ανάλυση (TGΑ), ενώ για τον χαρακτηρισμό των ενδιάμεσων και τελικών προϊόντων έγιναν μετρήσεις περίθλασης ακτίνων Χ (XRD), υπέρυθρης φασματοσκοπίας (FT-IR) και ηλεκτρονικής μικροσκοπίας σάρωσης (SEM). Στα τελικά προϊόντα έγινε ανάλυση της κρυσταλλικής δομής κατά Rietveld, προσδιορισμός όλων των χαρακτηριστικών μεγεθών (παράμετροι μοναδιαίας κυψελίδας, ατομικές θέσεις, αποστάσεις κλπ.) και απεικόνιση των κρυσταλλικών πλεγμάτων. Τέλος μετρήθηκε η αγωγιμότητα των ενώσεων. Όπως προέκυψε, με την εφαρμογή της τεχνικής πολυμερισμού των αρχικών διαλυμάτων είναι δυνατή η παραλαβή καθαρών ενώσεων La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) ύστερα από έψηση στους 1400οC για 20 h. Πρώτη φορά στη βιβλιογραφία αναφέρεται η παραλαβή καθαρού τελικού προϊόντος για την ένωση La9.83Si6O26+δ, La9.38Sr0.45Si6O26+δ, La9.33Sr0.50Si6O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ και La9.33Sr0.50Si5.70Al0.30O26+δ. Το γεγονός αυτό αυξάνει το εύρος στοιχειομετριών επιτυχούς σύνθεσης για τις ενώσεις πυριτικού Λανθανίου με δομή Απατίτη. Η σύνθεση των ενώσεων με τη μέθοδο του πολυμερισμού των αρχικών διαλυμάτων επηρεάζεται σημαντικά από τις αναλογίες των αρχικών αντιδραστηρίων. Μία μετατροπή του μοριακού λόγου κιτρικό οξύ:μεταλλοκατιόντα από 2 σε 3.3 και μείωση του λόγου διαλύτη:αρχικά αντιδρώντα από 0.21 – 0.28 σε 0.14 οδήγησε σε καθαρά τελικά προϊόντα για τις ενώσεις La9.33Si6O26, La9.68Sr0.15Si5.85Al0.15O26+δ, La9.53Sr0.30Si5.70Al0.30O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ και La9.38Sr0.45Si5.55Al0.45O26+δ ύστερα από έψηση στους 800 οC για 3 h. Είναι η πρώτη φορά που οι ενώσεις La9.68Sr0.15Si5.85Al0.15O26+δ, La9.53Sr0.30Si5.70Al0.30O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ και La9.38Sr0.45Si5.55Al0.45O26+δ παραλαμβάνονται καθαρές σε τόσο χαμηλή θερμοκρασία. Η ανάλυση της δομής κατά Rietveld έδειξε πως οι ενώσεις La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) κρυσταλλώνονται στο εξαγωνικό σύστημα με ομάδα συμμετρίας χώρου την P63/m. Η υποκατάσταση στην θέση του Si έχει σημαντικότερη επίδραση στα μέσα μήκη δεσμών σε σύγκριση με την υποκατάσταση στην θέση του La. Εξετάσθηκε η πιθανότητα ύπαρξης πλεονάζοντος οξυγόνου σε ενδιάμεσες θέσεις του κρυσταλλικού πλέγματος και βρέθηκε πως εντοπίζεται στην περιφέρεια των εξαγωνικών καναλιών που διατρέχουν τη δομή γεγονός που ενισχύει τη θεώρηση για διάχυση ιόντων μέσω μιας ημιτονοειδούς τύπου διαδρομής μέσα από τα εξαγωνικά κανάλια. Η διατομή των προαναφερθέντων καναλιών έχει σημαντική επίδραση στην ιοντική αγωγιμότητα των ενώσεων και συγκεκριμένα μια αύξηση της διατομής ευνοεί τις τιμές αγωγιμότητας. Η υποκατάσταση του La από Sr οδηγεί σε μείωση του μεγέθους των καναλιών ενώ αντίθετη επίδραση έχει η υποκατάσταση του Si από Al. Οι ηλεκτρικές ιδιότητες των ενώσεων πυριτικού Λανθανίου με δομή Απατίτη La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) σχετίζονται σε μεγάλο βαθμό με την διατομή των εξαγωνικών καναλιών οξυγόνου και την ποσότητα πλεονάζοντος οξυγόνου. Η ύπαρξη μιας βέλτιστης αναλογίας μεγέθους καναλιών και ποσότητας οξυγόνου στη δομή των ενώσεων ενισχύει την διάχυση. Σημαντική επίδραση στην αγωγιμότητα έχει η ύπαρξη δευτερευόντων φάσεων καθώς και η πυκνότητα των δειγμάτων. Οι ενώσεις La9.83Si6O26+δ και La9.38Sr0.45Si5.70Al0.30O26+δ εμφανίζουν τις μεγαλύτερες τιμές ιοντικής αγωγιμότητας στους 700 οCμε 11 και 14 mS/cm και τιμές ενέργειας ενεργοποίησης 0.52 και 0.55 eV, αντίστοιχα Οι ενώσεις La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) εμφανίζουν, κυρίως, δύο διαφορετικούς μηχανισμούς ιοντικής αγωγιμότητας. Η διαφοροποίηση αυτή σχετίζεται με την ύπαρξη δύο περιοχών τιμών ενέργειας ενεργοποίησης σε χαμηλές και υψηλές θερμοκρασίες. Ο μηχανισμός στις χαμηλές θερμοκρασίες λειτουργεί μέσω κενών θέσεων οξυγόνου και της περιορισμένης κίνησης του πλεονάζοντος οξυγόνου, το οποίο βρίσκεται παγιδευμένο ενώ σε υψηλές θερμοκρασίες μέσω αποκλειστικά από την μετακίνηση πλεονάζοντος οξυγόνου. Οι ενώσεις La9.33Si6O26, La9.68Sr0.15Si6O26+δ, La9.53Sr0.30Si6O26+δ, La9.68Sr0.15Si5.85Al0.15O26+δ και La9.53Sr0.30Si5.70Al.30O26+δ, δεν ακολούθησαν την παραπάνω συμπεριφορά και εμφάνισαν υψηλές τιμές ενέργειας ενεργοποίησης και χαμηλές τιμές ιοντικής αγωγιμότητας για όλο το εύρος των θερμοκρασιών., Apatite type lanthanum silicates with general formula La9.33+xSi6O26+δ is a newly reported family of compounds which exhibits high ionic conductivity at intermediate temperatures and is considered as promising electrolytes for IT-SOFCs. The structure of these compounds permits a wide range of cation/anion non stoichiometry. It is well established that fully stoichiometric systems e.g. La8Sr2Si6O26 have much lower conductivities and higher activation energies than systems containing either cation vacancies (La9.33Si6O26) or oxygen excess (La9Sr1Si6O26.5). Lately, research groups focus their studies on compounds with both cation vacancies and oxygen excess, in an attempt to further enhance their ionic conductivity. The subject of this thesis has to do with the La9.83-x-zSrxSi6-yAlyO26+δ (0x,y,z0.50) group of compounds and especially with the selection of the most suitable synthetic route, the synthesis of pure final products, the refinement of their crystal structure, the measurement of specific electrical properties and the correlation of the stoichiometry with their structure and properties. All compounds were prepared via a polymeric precursor route where citric acid and ethylene glycol are used as chelating and complexing agents, respectively. Microwave heating is used for the preparation of the precursors and is also tested for their final sintering. The intermediate and final products were examined by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The unit cell, the atomic positions, the length and angle of chemical bonds and the representation of crystal structures were determined by means of Rietveld structure refinement. Finally, ionic conductivity was measured by means of impedance spectroscopy. As it was concluded, pure La9.83-x-zSrxSi6-yAlyO26+δ (0x,y,z0.50) compounds can be prepared through the modified Pechini route after calcination at 1400°C for 20 h. The stoichiometry seems to have a major effect on the structure of the precursors, the dissociation of the polymeric network as well as the structure of final products and the amount of secondary faces.To the best of our knowledge, there is no previous literature on the successful synthesis and detailed structural analysis of La9.83Si6O26+δ, La9.38Sr0.45Si6O26+δ, La9.33Sr0.50Si6O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ and La9.33Sr0.50Si5.70Al0.30O26+δ compound. The synthesis is strongly affected by the ratios of starting materials. A modification of the molar ratio, citric acid to total cations, from 2 to 3.3 as well as a reduction in the molar ratio of solvent to starting materials 0.21 – 0.28 to 0.14 led to the preparation of pure final products for La9.33Si6O26, La9.68Sr0.15Si5.85Al0.15O26+δ, La9.53Sr0.30Si5.70Al0.30O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ and La9.38Sr0.45Si5.55Al0.45O26+δ after calcination at 800°C for 3 h. This is the first time that pure La9.68Sr0.15Si5.85Al0.15O26+δ, La9.53Sr0.30Si5.70Al0.30O26+δ, La9.38Sr0.45Si5.70Al0.30O26+δ and La9.38Sr0.45Si5.55Al0.45O26+δ compounds are prepared in such a low temperature. Rietveld analysis showed that La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) compounds crystallize in P63/m space group which owns hexagonal symmetry. The increase in Al doping on Si side exhibits more pronounced effect in the length of chemical bonds in comparison to Sr doping on La side. Moreover, it was concluded that interstitial oxygen accommodates a position at the periphery of the hexagonal channels in the vicinity of the SiO4 groups. This result enforces the theory that ion conduction in apatite lanthanum silicates takes place through a sinusoidal like diffusion of interstitial oxygen. Ion conduction is close related with the size of the hexagonal channels. An enlargement of the hexagonal channels leads in the enhancement of ionic conductivity. It was concluded that an increase in the Sr content reduces the size of the hexagonal channels while an increase in Al content has the opposite effect. The electrical properties of La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) compounds are affected in a major extent by the size of the hexagonal channel as well as the interstitial oxygen content. The existence of an optimum proportion between the size of the hexagonal channels and the interstitial oxygen content enhances the ionic conductivity. The La9.83Si6O26+δ and La9.38Sr0.45Si5.70Al0.30O26+δ compounds exhibit the higher values of ionic conductivity at 700 οC with 11 and 14 mS/cm and activation energy of 0.52 and 0.55 eV, respectively. La9.83-x-zSrxSi6-yAlyO26+δ (0≤x,y,z≤0.5) compounds represent two different ion conduction mechanisms. The low temperature migration mechanism has to do with a combination of diffusion through oxygen vacancy positions and limited diffusion through interstitial oxygen which it remains trapped while the high temperature conduction mechanism is materialized through the motion of the untrapped interstitial oxygen. La9.33Si6O26, La9.68Sr0.15Si6O26+δ, La9.53Sr0.30Si6O26+δ, La9.68Sr0.15Si5.85Al0.15O26+δ and La9.53Sr0.30Si5.70Al.30O26+δ compounds didn’t have the same behavior, exhibiting one mechanism in the whole temperature range which led in low values of conductivity and high values of activation energy., Δημήριος Θ. Κιούπης

International audience; A structural investigation of Agx(Ge0.25Se0.75)100 x glasses with x¼5, 15, and 25 at.% has been carried out by neutron diffraction and ab initio molecular dynamics (AIMD) simulation. A structural model for the glasses has been proposed: the Ge(Se1/2)4 tetrahedra would remain the fundamental structural units in all samples. The introduction of Ag in the Ge0.25Se0.75 network would lead to a decrease in homopolar Se-Se bonds and appearance of Ge-Ge bonds. A strong evolution in the Ag-Ag correlations upon introduction ofAg was observed with the Ag-Ag correlation distances changing from 4.4A for the Ag-poor glass to 3.0A for the Ag-rich ones. Such information was used to discuss the evolution of conductivity with Ag content in these glasses.

Gadolinium-ceria solid solution nanowires with tunable composition have been prepared through template cathodic electrodeposition from solutions containing Ce 3+Gd 3+ in a variable ratio. The employed template is Porous Anodic Alumina because it can function as thermal resistant separator supporting the nanowires if used as ionic conductor in Solid Oxide Fuel Cell (SOFC). Scanning Electron Microscopy of the deposited nanostructures revealed that the use of ethanol as solvent and metal chloride as electrolyte allowed to prepare continuous, compact and well defined nanowires with morphological features stable even after thermal treatment. EDX compositional analysis confirms the presence of both Ce and Gd in the nanowires with an atomic ratio very close to the Ce/Gd in the electrodeposition bath. X-ray diffraction analysis and Raman Spectroscopy revealed the formation of a solid solution of Gd-Ce oxide nanowires.

We present the observation of glass-like dynamic correlations of mobile mercury ions in the ionic conductor Cu2HgI4, detected in both NMR and nonlinear conductivity experiments. The results show that dynamic cooperativity appears in systems seemingly unrelated to glassy and soft arrested materials. A simple kinetic two-component model is proposed, which seems to provide a good description of the cooperative ionic dynamics., Comment: 5+2 pages (including supplemental material) This is final, accepted version

Thermogravimetric analysis (TGA) technique in controlled oxygen partial pressure (pO 2) atmospheres has been used to obtain equilibrium oxygen content data as a function of pO 2 on the La 2Mo 2O 9-δ system resulting from the partial reduction of fast oxide-ion conductor La 2Mo 2O 9 (LM). Thermodynamic conditions for stabilization of crystalline La 7Mo 7O 30 and amorphous La 2Mo 2O 7-y at 718 °C have been determined and discussed. At 608 °C, the compound reported for the first time La 2Mo 2O 8.96 (LM896) has been found. The crystalline form and transition temperature in LM896 have been identified by X-ray diffraction at room temperature (XRD) and at controlled temperature. Conductivity curves obtained by electrochemical impedance spectroscopy (EIS) as a function of temperature for both LM and LM896 have been compared. The results indicate that LM896 is a mixed ionic and electronic conductor (MIEC). © 2012 The Royal Society of Chemistry. Fil: Vega Castillo, Jesus Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Ravella, Uday K.. Université du Maine; Francia Fil: Corbel, Gwenaël. Université du Maine; Francia Fil: Lacorre, Philippe. Université du Maine; Francia Fil: Caneiro, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

Melilite-type [A(2)](2)[B(I)](2)[B(II)(2)O(7)](2) gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa](2)[Ga](2)[Ga(2)O(7)](2), grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga(2)O(7)] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group P42(1)m(α, α, 0)00s(α, α, 0)000, α = 0.2160(5), with a subcell metric of a = 7.9383(2) A, c = 5.2641(3) A, onto which modulation vectors are superimposed: q(1) = α (a* + b*), q(2) = α (-a* + b*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible.

Memristive properties of thin film copper oxides with different grain sizes were characterized using tunneling atomic force microscopy (TUNA) and optical reflection measurements. The thin films containing copper ions of different chemical states were prepared by thermal oxidation of metallic copper thin films, deposited via magnetron sputtering onto silicon wafer substrates at an elevated temperature for various lengths of time. The TUNA measurements showed a memristive hysteresis in the I-V curves under an applied bias profile with an initial bias of -3.5V, a ramp up to 3.5V, and subsequent return to -3.5V. Histogram analysis of the barrier height distribution for the forward and backward bias indicated that the barrier height fluctuates in a narrow range of bias voltages that are related to electrochemical potentials for oxidation/reduction of copper ions. Changes in chemical state of copper atoms were identified by optical reflectance measurements in UV-VIS-NIR wavelength regions. The growth of the thin films, including grain size, were characterized by topographic AFM imaging and changes in optical absorption bands due to the quantum size confinement effects. The fluctuations in the I-V measurements are theorized to be results of electrochemical changes as mobile ions migrate along grain boundaries due to heterogeneities in grain orientation/structure. A subtle periodic behavior and the variability of the I-V data suggest a correlation with grain size distribution. The asymmetric distribution in the barrier height may indicate that a different probability for injecting an electron in and withdrawing an electron from the films.

This paper presents results for the conductivity of BaCe0.85Y0.15O2-δ (BCY15) measured by electrochemical impedance spectroscopy in wet hydrogen and in Air, as well as test results from the application of the material in a new dual membrane fuel cell configuration (“IDEAL Cell”), in which the water is produced and evacuated through a separate chamber. The conductivity of dense BCY15 in wet hydrogen atmosphere at 700 °C is 2.0 10-2 S/cm. The measured values in air are of the same order. Preliminary tests of the material in the new cell design, where the three types of conductivity (protonic, oxide ion and mixed) are used in different cell compartments, are successfully performed.

International audience; Platinum nanoparticles were dispersed by wet impregnation on YSZ (8 mol% Y2O3) an ionically conducting support. The Pt dispersion of a series of catalysts was determined by using H-2 pulse chemisorption. Temperature Programmed Reduction (TPR) experiments were performed to characterize the pre-reduction step before dispersion measurements. Finally, a fast and reliable procedure was defined for the Pt dispersion measurements consisting in a pre-reduction step in hydrogen at 500 degrees C before the H-2 pulse chemisorption performed at -28 degrees C. Reproducible Pt dispersion values were obtained in good agreement with those measured by pulse CO chemisorptions and static volumetric titration. In addition, the combination of Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy and TPR has evidenced the role of surface oxygen vacancies on YSZ support for both H-2 and CO chemisorptions.

Pulsed Laser Deposition technique was used to engineer heterostructures of Yttrium-stabilized Zirconia (YSZ) and Gadolinium-doped Ceria (GDC) on perovskite substrates like Neodymium Gallate (NGO) and Strontium Titanate (STO). Epitaxial superlattices of the same number of layers of both materials were deposited with each block thickness as thin as 2 unit cells up to 30 unit cells. X-ray diffraction (XRD) investigation of the (002) symmetrical reflection allowed to evaluate the amount of material deposited in each layer constituting the superlattices. (113) asymmetrical reflections were analyzed to investigate strain effects on YSZ and GDC lattice parameters, evidencing the cube on cube growth of these films.

Microscopic one-dimensional noninteracting model for the description of the energy spectrum of the ion subsystem in ionic conductor is considered. The processes of ionic hoppings are described in terms of Pauli operators. Time-dependent correlation functions (b(t)b⁺(0))j in Pauli operators are obtained using the exact numerical procedure known for time-dependent spin correlation functions. The frequency dependence of autocorrelation function J bb+(ω) is calculated and analysed at the wide range of temperatures. The frequency and temperature dependences of the one-particle density of states are investigated. Розглянуто мiкроскопiчну одновимiрну модель невзаємодiючих частинок для опису енергетичногоспектру iонної пiдсистеми в iонному провiднику. Процеси iонного перескоку описанi у термiнах операторiв Паулi. Використовуючи точний числовий метод, вiдомий для часових спiнових кореляцiйних функцiй, отримано часовi кореляцiйнi функцiї (b(t)b⁺(0))j в операторах Паулi. Обчислено i проаналiзовано частотну залежнiсть автокореляцiйної функцiї J bb+(ω) в широкому iнтервалi температур. Дослiджено частотну i температурну залежностi одночастинкової густини станiв.

[ES] En este trabajo se presentan los resultados preliminares sobre películas delgadas de YSZ obtenidas mediante la nueva técnica de MOCVD de inyección pulsada para su aplicación como electrolitos sólidos. La originalidad de esta técnica consiste en la preparación e introducción de la fase vapor que se realiza mediante la inyección pulsada de micro-gotas de la solución líquida, que contiene los precursores de los elementos a depositar, dentro de la zona de reacción. Las características de la gota: tamaño, concentración de la solución y frecuencia de inyección determinan el espesor y la micro-estructura de las capas obtenidas. Este método, además de muy reproducible, permite obtener fácilmente estructuras multicapas con bajos ritmos de crecimiento para epitaxias o con altos ritmos de crecimiento para la obtención de heteroestructuras. Se ha puesto a punto esta técnica para la obtención de capas densas de YSZ (circona estabilizada con itria), material comúnmente utilizado como electrolito sólido de alta temperatura en sondas de oxígeno, generadores de oxígeno y SOFC (pilas de combustible de estado sólido). Se pretende obtener dichos dispositivos en forma de multicapas del tipo ánodo/electrolito/cátodo. Para ello, se han depositado capas de YSZ sobre silicio para optimizar los parámetros de depósito pero también sobre sustratos porosos activos que puedan actuar como electrodo en los dispositivos anteriormente descritos., [EN] In this work, we describe the preparation of YSZ layers on porous and non-porous substrates using the Pulsed Injection MOCVD technique for solid electrolyte applications. In this technique, the vapour phase is obtained by injecting micro-droplets of the desired solution delivered from a container kept at room temperature into a heated evaporator connected to a deposition chamber. The droplet characteristics, volume, precursor concentration and injection frequency will control and determine the thickness and the microstructure of the layers. The system offers a high degree of repeatability of the liquid volume injected and thus a high reproducibility of the layers from low to high growth rates. This process has been optimised in order to obtain dense YSZ membranes to be used as solid electrolytes in SOFC, oxygen generators and oxygen sensors. Future work will consist in the preparation of anode-electrolyte-cathode multilayered devices. For this purpose, experimental parameters have been studied and optimised in order to obtain thin YSZ membranes on dense and porous substrates., Este trabajo ha sido parcialmente financiado por la red temática europea Multimetox G5RT-CT-2000-05001.

BaMMn7O16 (M = Mg, Mn, Fe, Ni) and AMn8O16 (A = Ba, K2) hollandite oxides were synthesized in air from metal carbonates and a mixture of simple oxides using the thermal decomposition in solid phase method at 850 C. The oxides BaMn8O16 and BaFeMn7O16 crystallized in the hollandite monoclinic phase, S.G. I2/m and S.G. P2(1)/n respectively, whereas K2Mn8O16 was tetragonal, S.G. I4/m. Two new phases are reported: BaMgMn7O16 and BaNiMn7O16 which crystallize in the hollandite monoclinic phase structure. The ionic distributions were proposed on the basis of several physicochemical analyses comporting XRD, GTA, magnetic susceptibility and oxidation power measurements. Barium and potassium manganites showed Mn3+ and Mn4+ in octahedral sites whereas BaMMn7O16 (M = Mg, Ni) exhibited Mn2+ and Mn4+ in sites B. On the other hand, iron-manganese hollandite, BaFeMn7O16, shows Fe3+ ions besides Mn3+ and Mn4+ cations Se sintetizaron a 850 ºC en aire , óxidos de estructura holandita de fórmula BaMMn7O16 (M = Mg, Mn, Fe, Ni) y AMn8O16 (A = Ba,K2), usando como precursores carbonatos metálicos y una mezcla de óxidos simples, mediante la técnica de descomposición térmica en fase sólida. Los óxidos BaMn8O16 and BaFeMn7O16 cristalizaron en la fase holandita monoclínica, grupo espacial I2/m y P2(1)/n respectivamente, mientras que el óxido K2Mn8O16 presenta una estructura holandita tetragonal, grupo espacial I4/m. Se informa de dos nuevos óxidos, BaMgMn7O16 y BaNiMn7O16, que cristalizaron en la estructura holandita monoclínica. Se proponen las respectivas distribuciones iónicas sobre la base de análisis fisicoquímicos como: DRX, ATG, susceptibilidad magnética y poder de oxidación. Manganitas de bario y de potasio presentan en los sitios octaédricos de la estructura los iones Mn3+ y Mn4+ mientras que los óxidos de fórmula general BaMMn7O16 (M = Mg, Ni) muestran iones Mn2+ and Mn4+ en tales sitios. Por otra parte, el óxido BaFeMn7O16 presenta además de los iones Mn3+ y Mn4+, los iones Fe3+ en los sitios octaédricos B estructurales

Li diffusion in nano- and microcrystalline (1-x)Li2O:xB2O3 composites was investigated with impedance and NMR spectroscopy in the temperature range from 140 K to 500 K. Impedance results for the nanocrystalline system differ drastically from those of the microcrystalline system and show an enhancement of the dc conductivity when adding the insulator B2O3 to the ionic conductor Li2O. 7Li NMR lineshape measurements confirm that this is due to an enhanced fraction of mobile ions in the interfacial regions between the conductor and the insulator. Activation energies obtained from the dc conductivity (0.95 eV) and the 7Li NMR relaxation rate T1-1 (0.29 eV) are independent of the composition of the composites. © 2001 Scitec Publications.

The first-order Raman spectrum of K 2 S was measured over the temperature range from 10 to 742 K. The temperature dependence of the linewidth can be explained using results from the anharmonic lattice dynamics approach. Both the cubic and the quartic anharmonic interactions are of importance for this system. At 293 K, the Raman line is at ω T 2g =128 cm −1 with a full width at half maximum Γ T 2g =2.9 cm −1 .