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Las pilas de combustible de óxido sólido (SOFC) son dispositivos de generación eléctrica mediante la reacción entre un combustible (H2, CH4, etc...) y un comburente (O2) sin combustión directa, lo que incrementa la eficiencia de conversión respecto a los sistemas convencionales (ciclo de Carnot) que operan por debajo de 1073 K. El aprovechamiento del calor residual mediante ciclos de calor combinados eleva la eficiencia por encima del 85%. Las pérdidas óhmicas de las celdas SOFC están asociadas principalmente a la resistencia eléctrica de los electrolitos sólidos, pero la física que gobierna las pérdidas por sobrepotencial en los electrodos, especialmente en el cátodo, sigue siendo un tema de gran importancia en las investigaciones en materiales para SOFC. La reducción del oxígeno en el cátodo es el proceso cinéticamente limitante de la reacción total en la celda. Por otro lado, los mecanismos de actividad catalítica de los materiales frente a la reacción de reducción del oxígeno (ORR) no están bien establecidos y son objeto de intensas investigaciones experimentales y teóricas..., Solid oxide fuel cells (SOFC) are electrical generation devices by reaction between a fuel (H2, CH4,etc...) and an oxidizer (O2) without direct combustion, improving conversion efficiency compared to conventional systems (Carnot cycle) below 1073 K. The use of residual heat by means of combined heat cycles raises the efficiency above 85%.The ohmic losses of SOFC cells are mainly associated with the electrical resistance of the solid electrolytes, but the physics governing the overpotential losses in the electrodes, mostly in the cathode, remains being a topic of great importance in the research for SOFC materials. Oxygen reductionat the cathode is the kinetically limiting process of the overall reaction in the cell. On the other hand, the catalytic activity mechanisms of the materials against the oxygen reduction reaction (ORR) are not well established and are the subject of intense experimental and theoretical research...

Layered-type perovskites have been the focus of research in the last few years due to their outstanding properties as solid oxide fuel cell oxygen electrodes. The synthesis of a new (GdBa)0.8Ca0.4Co0.6Fe1.4O6-d layered perovskite as a single phase as well as the crystal structure determination and catalytic activity for oxygen reduction is reported. Highly advanced methods of transmission electron microscopy have been used for structure determination at atomic resolution. The oxide shows a complex modulation of the crystal structure associated with layered-type ordering of the Gd, Ba and Ca atoms in combination with formation of different coordination polyhedra of the Fe and Co atoms. Location of the anion vacancies within particular highly ion-conducting layers of the crystal structure has been achieved by phase image reconstruction. This material exhibits excellent electrochemical behaviour and thermal stability for use as an air electrode in IT-SOFCs., Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

Two new perovskite compounds, NaLaInNbO6and NaLaInTaO6, have been synthesized. Both compounds havea rock-salt ordering of the In/Nb or In/Ta cations and a layeredordering of the Na/La. They are unusual among this family ofdoubly cation ordered perovskites for having a +3/+5combination ofB/B′oxidation states instead of a divalentcation and W6+. Synchrotron powder diffraction and electrondiffraction data show both compounds have tetragonal√2ap×√2ap×2apunit cells. The octahedral tilt system of thesecompounds is complicated and seems to vary depending on thelength scale considered. Bond valence considerations demon-strate that none of the tilt systems compatible with a tetragonalunit cell produce a stable structure. It is proposed that additionaloxygen displacements are occurring on a local scale. The XRDdata show that theB-site ordering is nearly complete in bothcases, while theA-site cations show a lower degree of order. Thetendency of theB′-cation to undergo a second order Jahn−Teller distortion is identified as having an influence over the degree ofA-site ordering. Transmission electron microscopy showsfragmentation into nanosized domains with perpendicular orientations of the layeredA-site cation ordering. Such structuresmay be polar over short length scales which could lead to interesting dielectric properties such as relaxor behavior. Theprospects forfinding new doubly cation ordered perovskites are also discussed, MINECO, Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

© 2022 Elsevier B.V. E. García-González and S. García-Martín thank MICINN/AEI for funding the project PID2019-106662RB-C44/ AEI /10.13039/501100011033 and R.Weigand thanks MINECO/AEI for funding the project FIS2017-87360-P. O. Pérez-Benito acknowledges a predoctoral contract from UCM (call CT63/19-CT64/19). We acknowledge the help of O. Contreras in the development of the synthesis experiments. We will always be indebted to Professor E. Morán for the knowledge transmitted, he left us too early, untimely., Polar Na_(0.95)Er_(0.05)Nb_(0.9)Ti_(0.1)O_(3) perovskite has been synthesized as a nanostructured material by microwave assisted hydrothermal method. The characterization indicates that erbium is a constituent of the crystal structure and is preferentially located in sodium positions. The compound combines the nonlinear optical properties of the host (NaNb_(0.9)Ti_(0.1)O_(2.95) and the fluorescent properties of the Er^(3+)-dopant. Under excitation by a single femtosecond (< 10 fs) laser in the near-infrared region, simultaneous dual emission signals of second harmonic generation (SHG) and up-converting fluorescence (UCF) are observed and the nonlinear dependencies of the SHG and UCF intensities on the excitation intensity are measured. In addition, both emissions are shown to be sensitive to the chirp of the exciting pulses, and for UCF, it can be explained by means of a simple theoretical model based on the density matrix equations. These nano-structured particles with chirp-dependent dual behavior can be very advantageous when used in biological systems, since they can provide complementary information in different spectral ranges and tissues and are susceptible of coherent control, which can be both useful in optical microscopy and bioimaging., Ministerio de Ciencia e Innovación (MICINN)/AEI, Ministerio de Economía y Competitivdad (MINECO)/AEI, Universidad Complutense de Madrid, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

CRUE-CSIC (Acuerdos Transformativos 2021), The antiferromagnetic behavior of Fe3+ oxides of composition RE1.2Ba1.2Ca0.6Fe3O8, RE2.2Ba3.2Ca2.6Fe8O21, and REBa2Ca2Fe5O13 (RE = Gd, Tb) is highly influenced by the type of oxygen polyhedron around the Fe3+ cations and their ordering, which is coupled with the layered RE/Ba/Ca arrangement within the perovskite-related structure. Determination of the magnetic structures reveals different magnetic moments associated with Fe3+ spins in the different oxygen polyhedra (octahedron, tetrahedron, and square pyramid). The structural aspects impact on the strength of the Fe-O-Fe superexchange interactions and, therefore, on the Neel temperature ( ́ TN) of the compounds. The oxides present an interesting transition from three-dimensional (3D) to two-dimensional (2D) magnetic behavior above TN. The 2D magnetic interactions are stronger within the FeO6 octahedra layers than in the FeO4 tetrahedra layers., Ministerio de Ciencia e Innovación (España), Ministerio de Educación, Cultura y Deporte (España), Institute for Chemical Research in Kyoto University, Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

Complex compositional and displacive modulations of the crystal structure of KLaMnWO6 are imaged with atomic resolution by means of scanning transmission electron microscopy (STEM). This oxide is stabilized by cation vacancies leading to a La1+x/3K1−xMnWO6 stoichiometry. Compositional modulation on both the K and La layers are revealed in the high-angle annular dark-field STEM (HAADF-STEM) images. The compositional modulation within the La layer is coupled with the modulation of the octahedral tilting, which is exposed by imaging of the anion sublattice in annular bright-field STEM (ABFSTEM) images. These complex modulations are accommodated in a 5√2ap × 5√2ap × 2ap perovskite-type structure, Agencia Estatal de Investigación (AEI)/Fondo Europeo de Desarrollo Regional (FEDER/UE), Microscopy Centre of the UCM, Center for Emergent Materials: an NSF MRSEC, Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

Inorganic perovskites exhibit many important physical properties such as ferroelectricity, magnetoresistance and superconductivity as well their importance as energy materials. Many of the most important energy materials are inorganic perovskites and find application in batteries, fuel cells, photocatalysts, catalysis, thermoelectrics and solar thermal. In all these applications, perovskite oxides, or their derivatives offer highly competitive performance, often state of the art and so tend to dominate research into energy material. In the following sections, we review these functionalities in turn seeking to facilitate the interchange of ideas between domains. The potential for improvement is explored and we highlight the importance of both detailed modelling and in situ and operando studies in taking these materials forward, National Natural Science Foundation of China, Chinese Academy of Science, Natural Science Foundation of Shanghai (China), Shanghai Science and Technology Commission (China), Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

The organic solvents that are widely used as electrolytes in lithium ion batteries present safety challenges due to their volatile and flammable nature. The replacement of liquid organic electrolytes by non-volatile and intrinsically safe ceramic solid electrolytes is an effective approach to address the safety issue. However, the high total resistance (bulk and grain boundary) of such compounds, especially at low temperatures, makes those solid electrolyte systems unpractical for many applications where high power and low temperature performance are required. The addition of small quantities of a polymer is an efficient and low cost approach to reduce the grain boundary resistance of inorganic solid electrolytes. Therefore, in this work, we study the ionic conductivity of different composites based on non-sintered lithium lanthanum titanium oxide (La0.5Li0.5TiO3) as inorganic ceramic material and organic polymers with different characteristics, added in low percentage (<15 wt.%). The proposed cheap composite solid electrolytes double the ionic conductivity of the less cost-effective sintered La0.5Li0.5TiO3., Ministerio de Ciencia e Innovación (MICINN), Ministerio de Ciencia e Innovación (MICINN)/CDTI, Ministerio de Ciencia e Innovación (MICCIN)/FEDER, Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

Ministerio de Economía y Competitividad (España), European Commission, Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

The organic solvents that are widely used as electrolytes in lithium ion batteries present safety challenges due to their volatile and flammable nature. The replacement of liquid organic electrolytes by non-volatile and intrinsically safe ceramic solid electrolytes is an effective approach to address the safety issue. However, the high total resistance (bulk and grain boundary) of such compounds, especially at low temperatures, makes those solid electrolyte systems unpractical for many applications where high power and low temperature performance are required. The addition of small quantities of a polymer is an efficient and low cost approach to reduce the grain boundary resistance of inorganic solid electrolytes. Therefore, in this work, we study the ionic conductivity of different composites based on non-sintered lithium lanthanum titanium oxide (La0.5Li0.5TiO3) as inorganic ceramic material and organic polymers with different characteristics, added in low percentage (<15 wt.%). The proposed cheap composite solid electrolytes double the ionic conductivity of the less cost-effective sintered La0.5Li0.5TiO3.

Two new perovskite compounds, NaLaInNbO6 and NaLaInTaO6, have been synthesized. Both compounds have a rock-salt ordering of the In/Nb or In/Ta cations and a layered ordering of the Na/La. They are unusual among this family of doubly cation ordered perovskites for having a +3/+5 combination of B/B′ oxidation states instead of a divalent cation and W6+. Synchrotron powder diffraction and electron diffraction data show both compounds have tetragonal √2ap × √2ap × 2ap unit cells. The octahedral tilt system of these compounds is complicated and seems to vary depending on the length scale considered. Bond valence considerations demonstrate that none of the tilt systems compatible with a tetragonal unit cell produce a stable structure. It is proposed that additional oxygen displacements are occurring on a local scale. The XRD data show that the B-site ordering is nearly complete in both cases, while the A-site cations show a lower degree of order. The tendency of the B′-cation to undergo a second order Jahn− Teller distortion is identified as having an influence over the degree of A-site ordering. Transmission electron microscopy shows fragmentation into nanosized domains with perpendicular orientations of the layered A-site cation ordering. Such structures may be polar over short length scales which could lead to interesting dielectric properties such as relaxor behavior. The prospects for finding new doubly cation ordered perovskites are also discussed., Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

Los óxidos mixtos con estructura tipo perovskita, de fórmula general ABO3, forman familias de compuestos de gran interés tanto desde el punto de vista científico como tecnológico. Esta estructura ofrece una gran variedad de posibilidades de sustitución de cationes en las posiciones A y/o B para formar sistemas complejos con dos o más tipos de cationes en ambas posiciones. Esta flexibilidad composicional está asociada a una flexibilidad estructural que permite acomodar la variedad de tamaños y estados de oxidación de los diferentes cationes. En este sentido, el orden de los cationes en posiciones A y B de óxidos con estructura derivada del tipo perovskita ha generado un gran interés en los últimos años debido a su gran impacto sobre las propiedades eléctricas y magnéticas, lo que los convierte en materiales con un gran interés funcional. Entre los diferentes modelos de orden que se pueden establecer, el orden de tipo laminar de los cationes en las posiciones A ha sido poco explorado por su mayor dificultad de estabilización. Un método eficaz para inducir este tipo de orden consiste en la co-existencia de vacantes aniónicas, que también pueden llegar a ordenarse, estableciendo un orden laminar adicional dentro de la subred aniónica con interesantes implicaciones en las propiedades de estos óxidos. El objetivo general de este trabajo ha consistido en preparar óxidos con estructura derivada de la perovskita, con orden laminar en ambas subredes, catiónica y aniónica, y estudiar los efectos del orden estructural en sus propiedades eléctricas y magnéticas...

Ln3Ni2RuO9 (Ln = La, Nd) oxides (prepared by a solid state metathesis route) adopt a monoclinic (P21/n) A2BB'O6 double perovskite structure wherein the two independent octahedral 2c and 2d sites are occupied by Ni2+ and (Ni2+1/3Ru5+2/3) cations, respectively. In contrast to the expected ferromagnetic behavior, Ln3Ni2RuO9 oxides show a spin-glass behavior without long range magnetic order down to 2 K. These results reveal the importance of competing nearest neighbor (NN), next nearest neighbor (NNN) and third nearest neighbor (third NN) interactions between the magnetic Ni2+ and Ru5+ ions in the partially ordered double perovskite structure that conspire to thwart the expected ferromagnetic order in these materials.

Los óxidos mixtos con estructura tipo perovskita, de fórmula general ABO3, forman familias de compuestos de gran interés tanto desde el punto de vista científico como tecnológico. Esta estructura ofrece una gran variedad de posibilidades de sustitución de cationes en las posiciones A y/o B para formar sistemas complejos con dos o más tipos de cationes en ambas posiciones. Esta flexibilidad composicional está asociada a una flexibilidad estructural que permite acomodar la variedad de tamaños y estados de oxidación de los diferentes cationes. En este sentido, el orden de los cationes en posiciones A y B de óxidos con estructura derivada del tipo perovskita ha generado un gran interés en los últimos años debido a su gran impacto sobre las propiedades eléctricas y magnéticas, lo que los convierte en materiales con un gran interés funcional. Entre los diferentes modelos de orden que se pueden establecer, el orden de tipo laminar de los cationes en las posiciones A ha sido poco explorado por su mayor dificultad de estabilización. Un método eficaz para inducir este tipo de orden consiste en la co-existencia de vacantes aniónicas, que también pueden llegar a ordenarse, estableciendo un orden laminar adicional dentro de la subred aniónica con interesantes implicaciones en las propiedades de estos óxidos. El objetivo general de este trabajo ha consistido en preparar óxidos con estructura derivada de la perovskita, con orden laminar en ambas subredes, catiónica y aniónica, y estudiar los efectos del orden estructural en sus propiedades eléctricas y magnéticas..., Mixed oxides with perovskite-type structure, of general formula ABO3, form families of compounds of great interest, not only from the scientific point of view but also from the technological one. This crystal structure offers a great variety of possibilities of cation substitution in the A and/or B sites to form complex systems with two or more different types of cations in both positions. The compositional suppleness of the perovskite is associated with its structural flexibility, which allows to accommodate a variety of sizes and oxidation states of the different cations. In this way, cationic ordering in the A and B sites of perovskite-related-type oxides has generated a great interest in the last few years due to its high impact on the electric and magnetic properties, which makes them promising multifunctional materials. Among the different ordering patterns which can be established, layered-type ordering in the A sites has been less explored because its stabilization is rather challenging. An effective approach to induce this kind of ordering consists of the co-existence of anionic vacancies, which can be located in particular positions of the structure leading to additional layered ordering within the anionic sublattice with tremendous implications in the properties of these oxides. In this work, the preparation of novel perovskite-related-type oxides was carried out with the aim of layered ordering within both cationic and anionic sublattices, and to study the effect of the structural ordering on the electric and magnetic properties...

The influence of rare earth (RE) elements on superconducting properties of the transition element (TE)-substituted TExCu1−xSr2RECu2Oy cuprates has not been sufficiently emphasized so far. In the case of molibdocuprates with the general formula Mo0.3Cu0.3Sr2RECu2Oy, all the RE element containing compounds except La, Ce, and Lu can be prepared at room pressure. The influence of the crystal structure on the superconducting properties after ozone oxidation of the present system is reported selecting three groups of RE elements attending to their different atom sizes: small (Yb and Tm), medium (Gd), and big (Nd and Pr). Advanced transmission electron microscopy, various diffraction techniques, and spectroscopic analysis have been used to demonstrate that the increase of structural disorder complemented with a decrease in the hole content play a major role in the vanishing of superconductivity within the present system., Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

Perovskite-related GdBaMnFeO5 and the corresponding oxidized phase GdBaMnFeO6, with long-range layered-type ordering of the Ba and Gd atoms have been synthesized. Oxidation retains the cation ordering but drives a modulation of the crystal structure associated with the incorporation of the oxygen atoms between the Gd layers. Oxidation of GdBaMnFeO5 increases the oxidation state of Mn from 2+ to 4+, while the oxidation state of Fe remains 3+. Determination of the crystal structure of both GdBaMnFeO5 and GdBaMnFeO6 is carried out at atomic resolution by means of a combination of advanced transmission electron microscopy techniques. Crystal structure refinements from synchrotron X-ray diffraction data support the structural models proposed from the TEM data. The oxidation states of the Mn and Fe atoms are evaluated by means of EELS and Mö ssbauer spectroscopy, which also reveals the different magnetic behavior of these oxides., Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub