Thermal Evolution and Stability of Pr2O3-doped ZrO2 Powder and Thin Films

AbstractZrO2 powders and films with 5, 8, 9 and 10mol % of Pr2O3 were prepared by a modified sol-gel method using liquid precursors. The thermal stability of the different phases is crucial in order to use this material in devices such as fuel cells, where the appearance of unwanted spurious phases causes a negative impact in the efficiency of such devices. DTA-TG and HT-XRD analysis carried out on the powders show that crystallization takes place around 500°C. Heat treatments over 1000°C produces destabilization of the initial crystallization cubic phase in the powders as well as in the films. However, aging treatments consisting in thermal cycles between room temperature and 750°C, which is the temperature of technological interest, do not affect the structure, the microstructure and the stresses state of the Pr-doped ZO2 thin films

Enhancement of optical absorption in multiferroic (1-x)PZT-xPFN thin films: Experiments and first-principles analysis

Multiferroic compounds have gained research attention in the field of ferroelectric photovoltaics due to the presence of transition-metal d states from magnetic ions, which tend to reduce the bandgap value. In this work, 0.5Pb(Zr0.52Ti0.48)O3 - 0.5Pb(Fe0.5Nb0.5)O3 PZTFN0.5 thin films were synthesized using a sol-gel route to investigate the effect of iron doping on optical and multiferroic properties. For comparative analysis, the end-member compositions, Pb(Zr0.52Ti0.48)O3 (PZT) and Pb(Fe0.5Nb0.5)O3 (PFN), were also synthesized under identical conditions. Our results revealed that the presence of Fe ions, besides inducing multiferroic behavior, effectively enhances the optical absorption of the material in the visible light region. Optical transitions at 3.0 eV (2.4 eV) and 2.7 eV (2.2 eV) for the direct (indirect) bandgap were determined for PZTFN0.5 and PFN, respectively, indicating that the absorption edges of the iron-containing films result more promising than PZT (Eg 3.6eV) for photovoltaic applications. Both PZTFN0.5 and PFN thin films exhibit multiferroic behavior at room temperature, with different electric and magnetic properties. While PZTFN0.5 presents saturated hysteresis loops with remanent polarization values around 10 uC/cm2 and magnetization of 1.6 emu/cm2, PFN displays significantly larger remanence (31 emu/cm2) but poorer ferroelectric properties due to the presence of leakage. Microscopic insights into the structural and electronic properties of the PZTFN0.5 solid solution were provided from first-principles calculations

La Historia de las Relaciones Internacionales: divergencias y convergencias con sus “disciplinas madres”

El presente artículo, mediante una revisión reflexiva de bibliografía relacionada, tiene el objetivo de pensar los nexos y distinciones entre la Historia, las Relaciones Internacionales (RRII), y la Historia de las Relaciones Internacionales (HRRII). Se realiza un recorrido histórico de las disciplinas mencionadas, para finalizar con algunas de las características principales que definen a la HRRII como tal, y permiten ubicarla –según sus características - dentro de la corriente historiográfica analista, aunque sin adscribir institucionalmente a ella. La intención principal es presentar el debate, o más bien, el diálogo general entre la Historia y las Relaciones Internacionales y sus convergencias en la HRRII en los orígenes de esta última.The present article, through a reflexive revision of related bibliography, has as its aim to perceive the connections and distinctions between history, international relations and the history of international relations as a product of both. This involves a historical view via the disciplines mentioned, in order to end up with some of the main characteristics that define the history of international relations as such, and permit placing it-according to its characteristics-within the analytical current of historiography, although without becoming part of it. The primary goal is to present the debate, or rather, the general dialogue between history and international relations and their convergences in the history of international relations at the beginnings of the latter.Fil: Universidad Autónoma de QuerétaroFil: Universidad Autónoma de Querétar

Sol-gel synthesis and multiferroic properties of pyrochlore-free Pb(Fe0.5Nb0.5)O3 thin films

Lead iron niobate (PbFe0.5Nb0.5O3 - PFN) thin films were synthesized by a modified sol-gel route, which offers the advantage of a rapid, simple and non-toxic reaction method. Polycrystalline perovskite-structured PFN thin films without pyrochlore phases were obtained on Pt/Ti/SiO2/Si substrates after sintering by rapid thermal annealing at 650 {\deg}C. TEM and AFM images confirmed the excellent quality of the sintered film, while EDS spectroscopy revealed the presence of oxygen vacancies near the film/substrate interface. Electric measurements show good dielectric properties and ferroelectric behavior, characterized by typical C-V curves and well-defined P-E ferroelectric loops at 1 kHz, with remanent polarization values of ~12 uC/cm2. The polarization, however, increases with decreasing frequency, indicating the presence of leakage currents. I-V measurements show a significant increase in DC-conduction at relatively low fields (around 100 kV/cm). The films display ferromagnetic behavior at room temperature, with magnetic remanence around 30 emu/cm3 and a coercive field of 1 kOe. These values are significantly higher than those obtained for PFN powders fabricated by the same sol-gel route, as well as the magnetization values reported in the literature for epitaxial films.Comment: 24 pages, 10 figure

Mirando a Cuba desde Cuba Entrevista a Nuria Barbosa León

EntrevistaUniversidad Nacional de Rosari

Evolución microestructural en la preparación de materiales compuestos NiFe2O4-BaTiO3 por vía hidrotermal

La obtención de materiales monofásicos con respuesta ferroeléctrica y (anti-)ferromagnética simultánea y acoplada resulta problemática debido a limitaciones intrínsecas de tipo físico, estructural y electrónico. En este sentido una alternativa más realista, y en cierto modo con mayor flexibilidad a la hora de diseñar futuros dispositivos multiferroicos, consiste en preparar materiales compuestos en los cuales el acoplamiento magnetoeléctrico se puede alcanzar explotando los efectos interfaciales entre fases disimilares. Tal es el caso de los materiales compuestos basados en BaTiO3 (fase ferroeléctrica) y NiFe2O4 (fase magnética), que ya se han empezado a preparar fundamentalmente por medio de técnicas de deposición altamente energéticas. Sin embargo de cara a su aplicación práctica, sería interesante poder preparar esos materiales por métodos más sostenibles y menos costosos. De acuerdo con ello, en este trabajo se presenta un estudio preliminar en torno a la evolución microestructural experimentada por los materiales basados en NiFe2O4-BaTiO3 cuando son preparados mediante una técnica de procesamiento suave en disolución como es la síntesis hidrotermal. En concreto se ha analizado la influencia que diversos parámetros característicos del procesamiento hidrotermal pueden tener sobre la generación y distribución de fases e interfases durante la posterior consolidación térmica de estos materiales compuestos

Thermal evolution of CaO-doped HfO2 films and powders

Solid solutions of ZrO2 and HfO2 are potential electrolyte materials for intermediate-temperature SOFC because both are oxygen-ion conductors. The main challenge for these compounds is to reduce the relatively high value of the activation energies vacancies diffusion, which is influenced by several factors. In this work the thermal evolution of CaO-HfO2 materials have been investigated. (CaO)y-Hf(1-y)O(2-y) (y 0.06, 0.14 y 0.2) coatings and powders were synthesized by chemical solution deposition (CSD). Films were deposited onto alumina substrates by Dip Coating technique, the burning of organic waste was carried out at 500 °C under normal atmosphere and then the films were thermally treated at intervals of temperature rising to a maximum temperature of 1250 °C. By means Glazing Incidence X-ray Diffraction (ρ-2θ configuration) the phases were studied in the annealed films. On the other hand, the thermal evolution and crystallization process of powders were analyzed in-situ by HT-XRD. The phenomena crystallization occurred in films and powders were analyzed. The activation energies of diffusion of oxygen vacancies of HfO2-14 mole% CaO and HfO2-20 mole% CaO films were measured from the thermal evolution of the relaxation constant measured by Perturbed Angular Correlation Technique.Facultad de Ciencias ExactasFacultad de Ciencias Agrarias y Forestale

Repuesta ferro-piezoeléctrica de KNN-LTS poroso

La obtención de materiales monofásicos con respuesta ferroeléctrica y (anti-)ferromagnética simultánea y acoplada resulta problemática debido a limitaciones intrínsecas de tipo físico, estructural y electrónico. En este sentido una alternativa más realista, y en cierto modo con mayor flexibilidad a la hora de diseñar futuros dispositivos multiferroicos, consiste en preparar materiales compuestos en los cuales el acoplamiento magnetoeléctrico se puede alcanzar explotando los efectos interfaciales entre fases disimilares. Tal es el caso de los materiales compuestos basados en BaTiO3 (fase ferroeléctrica) y NiFe2O4 (fase magnética), que ya se han empezado a preparar fundamentalmente por medio de técnicas de deposición altamente energéticas. Sin embargo de cara a su aplicación práctica, sería interesante poder preparar esos materiales por métodos más sostenibles y menos costosos. De acuerdo con ello, en este trabajo se presenta un estudio preliminar en torno a la evolución microestructural experimentada por los materiales basados en NiFe2O4-BaTiO3 cuando son preparados mediante una técnica de procesamiento suave en disolución como es la síntesis hidrotermal. En concreto se ha analizado la influencia que diversos parámetros característicos del procesamiento hidrotermal pueden tener sobre la generación y distribución de fases e interfases durante la posterior consolidación térmica de estos materiales compuestos

Thermal evolution of CaO-doped HfO2 films and powders

Solid solutions of ZrO2 and HfO2 are potential electrolyte materials for intermediate-temperature SOFC because both are oxygen-ion conductors. The main challenge for these compounds is to reduce the relatively high value of the activation energies vacancies diffusion, which is influenced by several factors. In this work the thermal evolution of CaO-HfO2 materials have been investigated. (CaO)y-Hf(1-y)O(2-y) (y 0.06, 0.14 y 0.2) coatings and powders were synthesized by chemical solution deposition (CSD). Films were deposited onto alumina substrates by Dip Coating technique, the burning of organic waste was carried out at 500 °C under normal atmosphere and then the films were thermally treated at intervals of temperature rising to a maximum temperature of 1250 °C. By means Glazing Incidence X-ray Diffraction (ρ-2θ configuration) the phases were studied in the annealed films. On the other hand, the thermal evolution and crystallization process of powders were analyzed in-situ by HT-XRD. The phenomena crystallization occurred in films and powders were analyzed. The activation energies of diffusion of oxygen vacancies of HfO2-14 mole% CaO and HfO2-20 mole% CaO films were measured from the thermal evolution of the relaxation constant measured by Perturbed Angular Correlation Technique.Facultad de Ciencias ExactasFacultad de Ciencias Agrarias y Forestale