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

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

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

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

Electric behavior of functional glasses based on TeO2

In this paper we study the structural and electrical behavior of glass-ceramic material of general formula: xMgO (1-x) (0.5V2O 5.0.5MoO3)2TeO2 (0≤x≤0.9) through measurements of density, molar volume, oxygen packing density (OPD), differential scanning calorimetry (DSC) and Raman spectroscopy: electric behavior was studied by impedance spectroscopy. We found that magnesium cation induces the growth of slightly crystallized areas inside the material. Those nanocrystallizations were detected to a greater extent by atomic force microscopy (AFM) and in lesser extent by X-ray diffraction (XRD). Regarding the electrical measurements, it can be established that magnesium cation does not act as good ionic conductor in this material.En este trabajo estudiamos la estructura de un material vítreo cuya fórmula general es: xMgO(1-x)(0.5V2 O5 .0.5MoO3)2TeO2 (0≤x≤0.9), mediante medidas de densidad, volumen molar, empaquetamiento denso de oxigeno (OPD), calorimetría diferencial de barrido (DSC) y espectroscopia Raman; el comportamiento eléctrico se estudió por medio de espectroscopia de impedancia. Encontramos que el catión magnesio induce el crecimiento de zonas levemente cristalizadas dentro del material. Dichas nanocristalizaciones pudieron ser detectadas en mayor medida por microscopia de fuerzas atómicas (AFM) y en menor medida se pudo observar en los patrones de difracción de Rayos X (DRX). Con respecto a las propiedades eléctricas, se puede establecer que el catión magnesio no actúa como buen conductor iónico en este material.Instituto de Física La Plat

Electric behavior of functional glasses based on TeO2

In this paper we study the structural and electrical behavior of glass-ceramic material of general formula: xMgO (1-x) (0.5V2O 5.0.5MoO3)2TeO2 (0≤x≤0.9) through measurements of density, molar volume, oxygen packing density (OPD), differential scanning calorimetry (DSC) and Raman spectroscopy: electric behavior was studied by impedance spectroscopy. We found that magnesium cation induces the growth of slightly crystallized areas inside the material. Those nanocrystallizations were detected to a greater extent by atomic force microscopy (AFM) and in lesser extent by X-ray diffraction (XRD). Regarding the electrical measurements, it can be established that magnesium cation does not act as good ionic conductor in this material.En este trabajo estudiamos la estructura de un material vítreo cuya fórmula general es: xMgO(1-x)(0.5V2 O5 .0.5MoO3)2TeO2 (0≤x≤0.9), mediante medidas de densidad, volumen molar, empaquetamiento denso de oxigeno (OPD), calorimetría diferencial de barrido (DSC) y espectroscopia Raman; el comportamiento eléctrico se estudió por medio de espectroscopia de impedancia. Encontramos que el catión magnesio induce el crecimiento de zonas levemente cristalizadas dentro del material. Dichas nanocristalizaciones pudieron ser detectadas en mayor medida por microscopia de fuerzas atómicas (AFM) y en menor medida se pudo observar en los patrones de difracción de Rayos X (DRX). Con respecto a las propiedades eléctricas, se puede establecer que el catión magnesio no actúa como buen conductor iónico en este material.Instituto de Física La Plat

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

International nosocomial infection control consortium (INICC) report, data summary of 36 countries, for 2004-2009

The results of a surveillance study conducted by the International Nosocomial Infection Control Consortium (INICC) from January 2004 through December 2009 in 422 intensive care units (ICUs) of 36 countries in Latin America, Asia, Africa, and Europe are reported. During the 6-year study period, using Centers for Disease Control and Prevention (CDC) National Healthcare Safety Network (NHSN; formerly the National Nosocomial Infection Surveillance system [NNIS]) definitions for device-associated health care-associated infections, we gathered prospective data from 313,008 patients hospitalized in the consortium's ICUs for an aggregate of 2,194,897 ICU bed-days. Despite the fact that the use of devices in the developing countries' ICUs was remarkably similar to that reported in US ICUs in the CDC's NHSN, rates of device-associated nosocomial infection were significantly higher in the ICUs of the INICC hospitals; the pooled rate of central line-associated bloodstream infection in the INICC ICUs of 6.8 per 1,000 central line-days was more than 3-fold higher than the 2.0 per 1,000 central line-days reported in comparable US ICUs. The overall rate of ventilator-associated pneumonia also was far higher (15.8 vs 3.3 per 1,000 ventilator-days), as was the rate of catheter-associated urinary tract infection (6.3 vs. 3.3 per 1,000 catheter-days). Notably, the frequencies of resistance of Pseudomonas aeruginosa isolates to imipenem (47.2% vs 23.0%), Klebsiella pneumoniae isolates to ceftazidime (76.3% vs 27.1%), Escherichia coli isolates to ceftazidime (66.7% vs 8.1%), Staphylococcus aureus isolates to methicillin (84.4% vs 56.8%), were also higher in the consortium's ICUs, and the crude unadjusted excess mortalities of device-related infections ranged from 7.3% (for catheter-associated urinary tract infection) to 15.2% (for ventilator-associated pneumonia). Copyright © 2012 by the Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved