Unraveling Bulk and Grain Boundary Electrical Properties in La0.8Sr0.2Mn1-yO3 Thin Films

Grain boundaries in Sr-doped LaMnO3 thin films have been shown to strongly influence the electronic and oxygen mass transport properties, being able to profoundly modify the nature of the material. The unique behaviour of the grain boundaries can be correlated with substantial modifications of the cation concentration at the interfaces, which can be tuned by changing the overall cationic ratio in the films. In this work, we study the electronic properties of La0.8Sr0.2Mn1-yO3 thin films with variable Mn content. The influence of the cationic composition on the grain boundary and grain bulk electronic properties is elucidated by studying the manganese valence state evolution using spectroscopy techniques and by confronting the electronic properties of epitaxial and polycrystalline films. Substantial differences in the electronic conduction mechanism are found in the presence of grain boundaries and depending on the manganese content. Moreover, the unique defect chemistry of the nanomaterial is elucidated by measuring the electrical resistance of the thin films as a function of oxygen partial pressure, disclosing the importance of the cationic local non-stoichiometry on the thin films behavior

El reconocimiento del derecho a la verdad en Argentina

Tesis dirigida por Ángel Sánchez Legido, y tutor Joaquín Alcaide Fernández. Investiga cuál fue el desarrollo del derecho a saber la verdad de los familiares de los desaparecidos sobre sus seres queridos, durante la época de la última dictadura militar en nuestro país. Reseña la realidad histórica existente en el momento en que se produjeron los hechos, el período 1976/1983 y también las fechas relevantes del período postdictatorial de transición democrática, llegando hasta la actualidad, fecha en la cual, se procedió a la declaración de la nulidad de las leyes de amnistía por el Congreso de la Nación Argentina, hecho que produjo la reapertura de las causas penales y la efectiva privación de libertad de quienes han sido los autores de estos crímenes en Argentina. Desarrolla a la desaparición forzada de personas como crimen de lesa humanidad desde la perspectiva del derecho internacional universal y regional, delito que por su propia naturaleza genera una situación de incertidumbre y necesidad de verdad. Obligación que comienza a verse satisfecha a partir del reconocimiento y plasmación de este derecho humano en el que mucho tuvieron que ver los órganos de protección y promoción regionales y universales de derechos humanos. Estudia y determina cual ha sido el largo y difícil camino recorrido por las víctimas hacia la tutela del derecho de los familiares en la lucha por el reconocimiento de su derecho a saber la verdad, a ejercer el duelo y a la memoria

Active layers based on vertically aligned nanostructures for SOFC applications

One of the most recent strategies to enhance the electrode performance is preparing composite materials leading to an increase of the triple-phase-boundary (TPB) length. In this work, thin films VANs based on (La0.8Sr0.2)0.98Fe0.8Ti0.2O3−δ-Ce0.9Gd0.1O1.95 (LSFT-GDC) deposited by PLD were obtained for their use as functional layers in Solid Oxide Fuel Cells (SOFCs).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Thin film oxide-ion conducting electrolyte for near room temperature applications

Stabilized bismuth vanadate thin films are presented here as superior oxide ionic conductors, for application in solid state electrochemical devices operating near room temperature. Widely studied in the 90s in bulk form due to their unbeatable ionic conduction, this family of materials was finally discarded due to poor stability above 500 °C. Here, we however unveil the possibility of using BiVCuO at reduced temperatures in thin film-based devices, where the material keeps its unmatched conduction properties and at the same time shows good stability over a wide oxygen partial pressure range

Vertically Aligned Nanostructures for SOFC applications

One of the most recent strategies to enhance the electrode performance is preparing composite materials leading to an increase of the triple-phase-boundary (TPB) length. On this way, heteroepitaxial nanocomposite films such as vertically aligned nanostructures (VANs) deposited by Pulsed Laser Deposition (PLD) are one of the most promising and recent approaches to obtain nanocomposite active layers for energy applications1. In this work, thin films VANs based on (La0.8Sr0.2)0.98Fe0.8Ti0.2O3−δ-Ce0.9Gd0.1O1.95 (LSFT-GDC) electrodes were obtained for their use as functional layers in Solid Oxide Fuel Cells (SOFCs).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Engineering Transport in Manganites by Tuning Local Non-Stoichiometry in Grain Boundaries

Interface-dominated materials such as nanocrystalline thin films have emerged as an enthralling class of materials able to engineer functional properties of transition metal oxides widely used in energy and information technologies. In particular, it has been proved that strain-induced defects in grain boundaries of manganites deeply impact their functional properties by boosting their oxygen mass transport while abating their electronic and magnetic order. In this work, the origin of these dramatic changes is correlated for the first time with strong modifications of the anionic and cationic composition in the vicinity of strained grain boundary regions. We are also able to alter the grain boundary composition by tuning the overall cationic content in the films, which represents a new and powerful tool, beyond the classical space charge layer effect, for engineering electronic and mass transport properties of metal oxide thin films useful for a collection of relevant solid state devices

Unveiling the outstanding oxygen mass transport properties of Mn-rich perovskites in grain boundary-dominated La0.8Sr0.2(Mn1-xCox)0.85O3-d nanostructures

Ion transport in solid-state devices is of great interest for current and future energy and information technologies. A superior enhancement of several orders of magnitude of the oxygen diffusivity has been recently reported for grain boundaries in lanthanum strontium manganites. However, the significance and extent of this unique phenomenon is not yet established. Here, we fabricate a thin film continuous composition map of the La0.8Sr0.2(Mn1-xCox)0.85O3-d family revealing a substantial enhancement of the grain boundary oxygen mass transport properties for the entire range of compositions. Through isotope-exchange depth profiling coupled to secondary ion mass spectroscopy, we show that this excellent performance is not directly linked to the bulk of the material but to the intrinsic nature of the grain boundary. In particular, the great increase of the oxygen diffusion in Mn-rich compositions unveils an unprecedented catalytic performance in the field of Mixed Ionic Electronic Conductors. These results present grain boundaries engineering as a novel strategy for designing highly performing materials for solid state ionics based devices

Isotope Exchange Raman Spectroscopy (IERS): a novel technique to probe physicochemical processes inin situsitu

We have developed a novel in situ methodology for the direct study of mass transport properties in oxides with spatial and unprecedented time resolution, based on Raman spectroscopy coupled to isothermal isotope exchanges. Changes in the isotope concentration, resulting in a Raman frequency shift, can be followed in real time, not accessible by conventional methods, enabling complementary insights for the study of ion transport properties of electrode and electrolyte materials for advanced solid-state electrochemical devices. The proof of concept and strengths of isotope exchange Raman spectroscopy (IERS) are demonstrated by studying the oxygen isotope back-exchange in gadolinium-doped ceria (CGO) thin films. Resulting oxygen self-diffusion and surface exchange coefficients are compared to conventional time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterisation and literature values, showing good agreement, while at the same time providing additional insight, challenging established assumptions. IERS captivates through its rapidity, simple setup, non-destructive nature, cost effectiveness and versatile fields of application and thus can readily be integrated as new standard tool for in situ and operando characterization in many laboratories worldwide. The applicability of this method is expected to consolidate our understanding of elementary physicochemical processes and impact various emerging fields including solid oxide cells, battery research and beyond