Search

We report the precise control of tunneling magnetoresistance (TMR) in devices of self-assembled core/shell Fe$_3$O$_4$/Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ nanoparticles ($0\leq x\leq 1$). Adjusting the magnetic anisotropy through the content of Co$^{2+}$ in the shell, provides an accurate tool to control the switching field between the bistable states of the TMR. In this way, different combinations of soft/hard and hard/soft core/shell configurations can be envisaged for optimizing devices with the required magnetotransport response., Comment: 25 pages, 7 figures

New LT-SOFC cathodes with La0.5-xPrxBa0.5CoO3-δ (0 ≤ x ≤ 0.5) compositions were studied. The La-rich compounds exhibit an inter-growing cubic and tetragonal structure whereas the Pr-rich show a tetragonal structure. Cathode polarization resistances, estimated from electrochemical impedance (EIS), take values around 0.15 and 0.04 Ω cm2 in air at 600 and 700 °C, respectively. The O2-reduction mechanism and its kinetic coefficients, O-ion diffusion (Dchem) and O-surface exchange (kchem), were studied by applying the ALS model for macro homogenous porous electrodes to the EIS data, in combination with microstructural parameters obtained from three-dimensional tomography using focused ion beam-scanning electron microscopy (3D FIB-SEM). The diffusion coefficients for samples with mixing of phases take values of Dchem ∼ 10-6 cm2 s-1, at 700 °C in air, whereas the pure tetragonal phases present lower values Dchem ∼ 10-8 cm2 s-1. On the contrary the kchem for all samples takes values ranging between 0.4 and 1 × 10-4 cm s-1 at 700 °C in air. In addition, the origin of time evolution of polarization at 700 °C in air was evaluated by combining the EIS spectra as a function of time and the ex situ sample characterization of fresh and tested samples by 3D FIB-SEM tomography and inductively coupled plasma-optical emission spectrometry (ICP-OES). Little changes of microstructures were detected, whereas an increasing of the amount of a water-soluble Ba surface species in comparison with total cation surface segregation was observed for all samples after the ageing. This may constitute the main reason causing the polarization resistance degradation. However, the analysis of time evolution shows, that contrary to the situations reported for SrO segregation in Sr-based perovskites, the Dchem is the coefficient mainly affected for compositions with inter-grown phases. At the same time, both Dchem and kchem decreases with time when only the tetragonal phase is present. Fil: Garcés, D.. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Wang, H.. Northwestern University; Estados Unidos Fil: Barnett, S.A.. Northwestern University; Estados Unidos Fil: Leyva, Adelma Graciela. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Napolitano, Federico Ricardo. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Fuentes, Rodolfo Oscar. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Troiani, Horacio Esteban. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Mogni, Liliana Verónica. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina

A mixed conducting oxide with a nominal composition Sr(Ti0.3Fe0.7Ru0.07)O3-δ (STFRu) is studied, in comparison with SrTi0.3Fe0.7O3-δ (STF) oxide, as an anode for solid oxide fuel cells. Exposing STFRu to reducing fuel conditions at 800 °C for 4 h results in the exsolution of essentially all of the Ru and a small fraction of the Fe from the oxide, and the formation of Ru1-xFex nanoparticles on the oxide surfaces. Most of the nanoparticles have the hexagonal structure expected for Ru-rich alloys, and thermogravimetric analysis suggests the composition x ∼ 0.2. A small fraction of bcc-structure, presumably Fe-rich, nanoparticles are also detected. Comparison of cells with STFRu and STF anodes shows that the presence of Ru induces a reduced polarization resistance and increases the maximum power density under most cell operating conditions, particularly at lower temperatures and hydrogen partial pressures. For example, at 700 °C and 30% H2 fuel, the maximum power density is 0.1 W cm-2 for STF compared to 0.3 W cm-2 for STFRu. There is also a significant change in the shape of the current-voltage curves and the pH2-dependence of the anode polarization resistances RP,A ∝ (pH2)-m, from m ∼ 0.5-1.0 for STF to m ∼ 0.11-0.29 for STFRu; these suggest that Ru1-xFex nanoparticles improve anode performance by promoting hydrogen adsorption. Fil: Glaser, R.. Northwestern University; Estados Unidos Fil: Zhu, T.. Northwestern University; Estados Unidos Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina Fil: Caneiro, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. YPF - Tecnología; Argentina Fil: Mogni, Liliana Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina Fil: Barnett, S.. Northwestern University; Estados Unidos

Electrically conducting oxides have been proposed as alternatives to Ni-based cermet anodes for solid oxide fuel cells (SOFCs) to overcome issues such as coking and impurity poisoning, but their electrochemical performance is typically inferior to that of Ni-based cermets. Here we show that a new oxide composition, Sr0.95(Ti0.3Fe0.63Ni0.07)O3−δ, yields anode polarization resistance competitive with Ni cermets, and substantially better than that of the corresponding Ni-free compound, SrTi0.3Fe0.7O3−δ. Exposure to fuel results in exsolution and nucleation of Ni0.5Fe0.5 nanoparticles uniformly dispersed on the Ni-substituted perovskite surface, whereas no nanoparticles are observed on SrTi0.3Fe0.7O3−δ. A general thermodynamic model is developed that quantitatively predicts exsolved nanoparticle composition. The reduction in anode polarization resistance by the nanoparticles, by as much as 4 times, is most pronounced at cell operating temperatures below 800°C and low H2 partial pressures, suggesting that the nanoparticles improve performance by promoting H2 adsorption. Mixed conducting perovskite oxides are proposed as alternatives for solid oxide fuel cell anodes, and in situ metallic nanoparticle precipitation/exsolution is considered to improve their performance. However, understanding of exsolution is still lacking, such as the reason why specific cations exsolve from an oxide anode and what determines the exsolved phase composition under various anode conditions. Here we directly compare Sr(Ti,Fe)O3-based anodes with and without exsolved metallic nanoparticles, showing their impact on electrochemical characteristics especially under low anode hydrogen concentrations and low temperatures. Three different methods are used to quantitatively determine the composition of the exsolved (Ni,Fe) nanoparticles, and for the first time demonstrate that this can be achieved through thermogravimetric analysis. This work is the first to propose a detailed thermodynamic theory predicting the exsolved nanoparticle composition with successful experimental verification. Ni-Fe nanoparticles are observed to exsolve from Ni-substituted Sr0.95(Ti0.3Fe0.63Ni0.07)O3−δ anode. The exsolved nanoparticles act to enhance hydrogen dissociative adsorption, yielding much lower anode polarization resistance and higher cell performance, especially under low pH2 and temperatures, which is comparable with the current Ni-based cermets. Fil: Zhu, Tenglong. Northwestern University; Estados Unidos. Nanjing University of Science and Technology; China Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina Fil: Mogni, Liliana Verónica. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Han, Minfang. Tsinghua University; China Fil: Barnett, Scott A.. Northwestern University; Estados Unidos

Conjugation of optical and magnetic responses in a unique system at the nanoscale emerges as a powerful tool for several applications. Here, we fabricated bifunctional CoFe2O4-core/ZnO-shell nanoparticles with simultaneous photoluminescence in the visible range and ac magnetic losses suitable for hyperthermia. The structural characterization confirms that the system is formed by a ≈7 nm CoFe2O4 core encapsulated in a ≈1.5-nm-thick semiconducting ZnO shell. As expected from its high anisotropy, the magnetic losses in an ac magnetic field are dominated by the Brown relaxation mechanism. The ac magnetic response of the core/shell system can be accurately predicted by the linear response theory and differs from that one of bare CoFe2O4 nanoparticles as a consequence of changes in the viscous relaxation process due to the effect of the magnetostatic interactions. Concerning the optical properties, by comparing core/shell CoFe2O4/ZnO and single-phase ZnO nanoparticles, we found that the former exhibits a broader optical absorption and photoluminescence, both shifted to the visible range, indicating that the optical properties are closely associated with the shell-morphology of ZnO. Being focused on bifunctional nanoparticles with an optical response in the visible range and a tunable hyperthermia output, our results can help to address current open questions on magnetic fluid hyperthermia. Fil: Lavorato, Gabriel Carlos. Centro Brasileiro de Pesquisas Físicas; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Lima, Enio Junior. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Vasquez Mansilla, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Troiani, Horacio Esteban. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Zysler, Roberto Daniel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Winkler, Elin Lilian. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina

A scalable, simple, robust and reproducible method is presented for the preparation of chemically homogeneous and ordered nanocrystalline and mesoporous Zr1-xCexO2 thin films. The method utilizes widely available commercial block copolymers as templates. We show how the preparation conditions, film compositions and thermal treatments determine the mesoporous and crystalline structure. Through the scanning of the synthetic process, it was possible to arrive at an optimized and very reproducible method which allows the preparation of high quality, transparent, nanocrystalline and ordered Zr1-xCexO2 mesoporous thin films with different compositions. Fil: Violi, Ianina Lucila. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Seguridad Nuclear y Ambiente. Gerencia de Química (CAC); Argentina Fil: Luca, Vittorio. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Soldati, Analía Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina Fil: Soler Illia, Galo Juan de Avila Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones no Nucleares; Argentina. Universidad Nacional de San Martin. Instituto de Nanosistemas; Argentina Fil: Zelcer, Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Seguridad Nuclear y Ambiente. Gerencia de Química (CAC); Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina

International audience; In the past decade, the surprising magnetic behavior of gold nanoparticles has been reported. This unexpected property is mainly attributed both to size and surface effects. Mesoporous thin films are ideal matrices for metallic nanoparticles inclusion, because of their highly accessible and tailorable pore systems that lead to completely tunable chemical environments. Exploiting these features, we synthesized Au nanoparticles within mesoporous titania thin films (film thickness of ∼150 nm and pore diameter of ∼5 nm), and we studied their magnetic properties under confinement. Here, we present the results of the magnetization as a function of temperature and magnetic field for this system, which are consistent with the previously reported for free (unconfined) thiol-capped gold nanoparticles. The successful inclusion of stable magnetic Au nanoparticles within transparent mesoporous thin films opens the gates for the application of these nanocomposites in two-dimensional (2D) microdevices technology and magneto-optical devices.

We present a crystallographic, morphologic and redox dynamic study on (60:40) NiO/Ce0.9Gd0.1O1.95 (NiO/GDC) cermets simulating Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) anodes in situ conditions. We tested micro- and nanometer sized materials at 700ºC in three different atmospheres (5% H2, 5% O2 and 20% CH4). We used Dispersive X-ray Absorption Spectroscopy (DXAS) analysisat the Ce L3-edge and at the Ni K-edge to follow the metal´s oxidation states. A correlation between the catalytic/redox properties and the sample´s characteristics (microstructure, Ni distribution, etc.) was found, indicating that nanometric sized particles showed faster and higher reduction extents than micrometric particles of the same composition. Fil: Fernandez Zuvich, Afra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Larrondo, Susana Adelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Química. Laboratorio de Procesos Catalíticos; Argentina Fil: Saleta, Martin. Laboratório Nacional de Luz Síncrotron; Brasil Fil: Napolitano, Federico Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Caneiro, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Arce, Mauricio Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Serquis, Adriana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Soldati, Analía Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

One of the remaining challenges for the solid oxide fuel cell (SOFC) technology is decreasing its operation temperature to the 500-800 °C range in a cost-effective way without diminishing the cell performance. In this work, we studied a symmetrical cell composed of Sr0.6La0.4Co0.8Fe0.2O3-δ (LSCFO) cathodes deposited on a Ce0.8Y0.2O2-δ (CYO) substrate by the simple, cost-effective and scalable spin coating technique. The nanostructured cathode is composed of agglomerated ∼100-200 nm particles with ∼50 nm crystallite size. Electrochemical impedance spectroscopy (EIS) analysis indicates that electrolyte grain boundary conductivity strongly depends on the cathode nature. The detailed high resolution transmission electron microscopy (HR-TEM) characterization of the LSCFO/CYO interface reveals that the LSCFO cathode is well adhered to the CYO electrolyte. The improved nano/microstructure of the cathodes and the cathode/electrolyte interface yields to cathode area specific resistance (ASR) values as low as 0.4 Ωcm2 at 550 °C, being these values even lower than those previously reported in literature for cathodes in optimized LSCFO/CYO/YSZ/CYO/LSCFO cells. Fil: Baque, Laura Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Padmasree, K.P.. Centro de Investigación y de Estudios Avanzados; México Fil: Ceniceros Reyes, M.A.. Centro de Investigación en Química Aplicada; México Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Serquis, Adriana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Soldati, Analía Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

In this work, we studied the dynamic and static magnetic properties of ZnO-core/CoFe2O4-shell and CoO-core/CoFe2O4-shell nanoparticles. Both systems are formed by a core of ∼4 nm of diameter encapsulated in a shell of ∼2 nm of thickness. The mean blocking temperature changes from 106(7) to 276(5) K when the core is diamagnetic or antiferromagnetic, respectively. Magnetic remanence studies revealed the presence of weak dipolar interparticle interactions, where Hint is approximately -0.1 kOe for ZnO/CoFe2O4 and -0.9 kOe for CoO/CoFe2O4, playing a minor role in the magnetic behavior of the materials. Relaxation experiments provided evidence that the magnetization reversal process of CoFe2O4 is strongly dependent on the magnetic order of the core. At 10 K, activation volumes of ∼46(6) and ∼69(5) nm3 were found for CoO/CoFe2O4 and ZnO/CoFe2O4 nanoparticles, respectively, corresponding to one-third and one-fifth of the total shell volume. While the magnetic behavior of ZnO/CoFe2O4 nanoparticles is strongly affected by the surface disorder, the exchange coupling at the CoO/CoFe2O4 interface rules the magnetization reversal and the nanoparticles' thermal stability by inducing a larger energy barrier and promoting smaller switching volume. Fil: Lavorato, Gabriel Carlos. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina. Argentine Italian Joint Laboratory of Nanomagnetism; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Consiglio Nazionale delle Ricerche; Italia Fil: Peddis, Davide. Argentine Italian Joint Laboratory of Nanomagnetism; Argentina. Consiglio Nazionale delle Ricerche; Italia Fil: Lima, Enio Junior. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina. Argentine Italian Joint Laboratory of Nanomagnetism; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Troiani, Horacio Esteban. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Agostinelli, Elisabetta. Argentine Italian Joint Laboratory of Nanomagnetism; Argentina. Consiglio Nazionale delle Ricerche; Italia Fil: Fiorani, Dino. Argentine Italian Joint Laboratory of Nanomagnetism; Argentina. Consiglio Nazionale delle Ricerche; Italia Fil: Zysler, Roberto Daniel. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina. Argentine Italian Joint Laboratory of Nanomagnetism; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Winkler, Elin Lilian. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina. Argentine Italian Joint Laboratory of Nanomagnetism; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina

The commercialization of Solid oxide fuel cells (SOFCs) is still hindered by their cost and long term degradation. One of the most common degradation mechanisms of La1-xSrxFe1-yCoyO3-d (LSCFO) cathodes reported in literature is element demixing. In this work, the degradation of LSCFO cathodes deposited on Ce1-xGdxO2-d electrolytes at 800°C in air for 50 h was investigated by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). EIS spectra from LSCFO cathodes present two contributions: one at high frequency and another at low frequency. The high frequency contribution remains invariable during the ageing treatment while the low frequency contribution continuously increases. The formation of small segregates was observed after the ageing treatment. Energy dispersive spectroscopy analysis reveals that these segregates were particularly poor in Sr. Fil: Baque, Laura Cecilia. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Soldati, Analía Leticia. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Troiani, Horacio Esteban. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Serquis, Adriana Cristina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Mge10 mol% LiBH4 composite plus small amounts of FeF3 is investigated in the present work. The presence of LiBH4 during the milling process noticeably modifies the size and morphology of the Mg agglomerates, leading to faster hydrogenation and reaching almost the theoretical hydrogen capacity owing to enhanced hydrogen diffusion mechanism. However, the dehydrogenation of the system at low temperatures (300 C) is still slow. Thus, FeF3 addition is proposed to improve the dehydrogenation kinetic behavior. From experimental results, it is found that the presence of FeF3 results in an additional size reduction of the Mg agglomerates between ~10 and ~100 mm and the formation of stable phases such as MgF2, LiF and FeB. The FeB species might have a catalytic effect upon the MgH2 decomposition. As a further result of the FeF3 addition, the Mge10 mol%LiBH4e5 mol% FeF3 material shows improved dehydrogenation properties: reduced dehydrogenation activation energy, faster hydrogen desorption rate and reversible hydrogen capacities of about 5 wt% at 275 C. Fil: Puszkiel, Julián Atilio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Centre for Materials and Coastal Research; Alemania Fil: Gennari, Fabiana Cristina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Arneodo Larochette, Pierre Paul. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Troiani, Horacio Esteban. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Karimi, Fahim. Centre for Materials and Coastal Research; Alemania Fil: Pistidda, Claudio. Centre for Materials and Coastal Research; Alemania Fil: Gosalawit e Utke, Rapee. Centre for Materials and Coastal Research; Alemania. Institute of Science, Suranaree University of Technology; Tailandia Fil: Jepsen, Julian. Centre for Materials and Coastal Research; Alemania Fil: Jensen, Torben R.. University of Aarhus; Dinamarca Fil: Gundlach, Carsten. University of Aarhus; Dinamarca Fil: Tolkiehn, Martin. HASYLAB at DES; Alemania Fil: Bellosta von Colbe, José. Centre for Materials and Coastal Research; Alemania Fil: Klassen, Thomas. Centre for Materials and Coastal Research; Alemania Fil: Dornheim, Martin. Centre for Materials and Coastal Research; Alemania

Metal-porous oxide nanocomposites present great interest in optical devices and heterogeneous catalysis. For these applications, particle shape and size control, as well as accessibility, are critical aspects. In this work, gold nanoparticles (NPs) were infiltrated into mesoporous TiO2 thin films (MTTF) by an impregnation-reduction method. In situ ellipsometry measurements were performed during thermal treatment to follow in real time the changes in the optical constants and thickness of the composites systems while being submitted to continuous heating at different rates, from room temperature up to 600 °C. Complementary characterization by UV–visible spectrophotometry, grazing incident wide angle scattering (GIWAXS), and X-ray reflectometry (XRR) were performed. TEM microscopy was used to analyze the morphological changes in the composite films after the thermal treatment. Our experiments demonstrate that particle coarsening starts at temperatures below 200 °C through the processes of ripening and particle migration, leading to changes in the particle size distribution (PSD) until a mechanical restriction, due to the porous geometry, induces a change of the particle shape from spherical to ellipsoidal. This results in an internal stress that swells the mesoporous film. The effect of the gold filling fraction and the heating ramp was analyzed. A mechanism based on the kinetics of particle migration and coalescence, through the modeling of the localized surface plasmon resonance under the dipolar approximation, is proposed to explain the changes in the optical properties of these composites materials and unravel the thermal activated processes occurring in metal crystallites supported on porous oxide frameworks. Fil: Martínez, Eduardo David. Comisión Nacional de Energía Atómica. Gerencia del Área de Seguridad Nuclear y Ambiente. Gerencia de Química (CAC); Argentina Fil: Cédric, Boissiere. College de France; Francia Fil: Grosso, David. College de France; Francia Fil: Sanchez, Clément. College de France; Francia Fil: Troiani, Horacio Esteban. Comision Nacional de Energia Atomica. Gerencia D/area de Energia Nuclear; Argentina Fil: Galo, J. A. A. Soler Illia. Comisión Nacional de Energía Atómica. Gerencia del Área de Seguridad Nuclear y Ambiente. Gerencia de Química (CAC); Argentina

Carbon-supported platinum nanoparticles Pt/C (NPs) are used in many fields of science. These kinds of materials have been extensively studied in electrochemistry due to the fact that they are applied in fuel cell technology. Although there are a myriad of methods for Pt NP synthesis, the need for obtaining Pt/C NPs with a good dispersion (covering over the entire support), a narrow size distribution, and clean surface (among other parameters) is far to be overcome. On this sense herein we describe a very easy and quick method of synthesis of highly dispersed Pt NPs followed by a simple electrochemical cleaning step. The catalysts were electrochemically characterized by studying their behavior in 0.5 M H2SO4 and also by using CO as a probe during the CO electro-oxidation reaction (COEOR). This paper shows how to obtain highly dispersed and clean Pt/C NPs that produce very reproducible results. Besides, we demonstrate how the presence of impurities negatively affects the electrochemical reproducibility of Pt NPs with a clear impact on their catalytic activity., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Since reactor pressure vessel steels are ferromagnetic, provide a convenient means to monitor changes in the mechanical properties of the material upon irradiation with high energy particles, by measuring their magnetic properties. Here, we discuss the correlation between mechanical and magnetic properties and microstructure, by studying the flux effect on the nuclear pressure vessel steel used in reactors currently under construction in Argentina. Charpy-V notched specimens of this steel were irradiated in the RA1 experimental reactor at 275 C with two lead factors (LFs), 93 and 183. The magnetic properties were studied by means of DC magnetometry and ferromagnetic resonance. The results show that the coercive field and magnetic anisotropy spatial distribution are sensitive to the LF and can be explained by taking into account the evolution of the microstructure with this parameter. The saturation magnetization shows a dominant dependence on the accumulated damage. Consequently, the mentioned techniques are suitable to estimate the degradation of the reactor vessel steel. Fil: Kempf, Rodolfo A.. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; Argentina Fil: Sacanell, Joaquin Gonzalo. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; Argentina Fil: Milano, Julian. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina Fil: Guerra Mendez, Nicolas. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; Argentina Fil: Winkler, Elin Lilian. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina Fil: Butera, Alejandro Ricardo. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina Fil: Troiani, Horacio Esteban. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina Fil: Saleta, Martin Eduardo. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina Fil: Fortis, Ana Maria. Comisión Nacional de Energía Atómica; Argentina

Controlling the structures of supports and supported phases is important for catalytic applications where synergic effects can play a main role. In this context, we present versatile methods for suitable microstructurization of CeO2 support and improved dispersion of supported Pt crystallites in a Pt/CeO2 system for enhanced catalytic oxidation of CO. The physicochemical properties investigated using SEM, BET, visible Raman, H2-TPR and OSC measurements demonstrated the important role played by the precursor on the properties of CeO2. Further, 0.5 wt% Pt deposited over CeO2 via ethylene glycol assisted reduction (EGR) was found to be more advantageous than conventional impregnation (IMP) in producing very finely dispersed Pt particles that did not noticeably sinter even after thermal treatment at 500 ◦C for longer duration. H2-chemisorption and H2-TPR experiments further substantiated better Pt dispersion on CeO2 prepared in the presence of Cl− ions regardless of the method employed, thus suggesting a strong microstructural effect of support during growth and anti-sintering activity of Pt crystallites. The CO oxidation activity additionally demonstrates that samples prepared by EGR method show remarkably better performance (100% conversion in

M/CeO2/YSZ nanocomposites (M = Ru, Pd, Ag) were prepared by successive impregnation and tested in the ethanol steam reforming (ESR). Ru/CeO2/YSZ demonstrated good activity and stability under reaction conditions. Pd/CeO2/YSZ shows good initial activity but suffers of significant deactivation while the performances of the Ag-based sample were rather poor. A plethora of different structural (Powder XRD), microstructural (HR-TEM), morphological (surface area, CO chemisorption) and thermal analysis characterization techniques were used to evidence the modification of the samples induced by prolonged exposure to the reaction mixture. The promising performances of Ru/CeO2/YSZ were associated to the combination of the positive action of the metal selectivity to syn-gas and of CeO2 in metal dispersion stabilization and coke deactivation prevention. (C) 2011 Elsevier B.V. All rights reserved.

Heavy metals from mining, smelting operations and other industrial processing facilities pollute wastewaters worldwide. Extraction of metals from industrial effluents has been widely studied due to the economic advantages and the relative ease of technical implementation. Consequently, the search for new and improved methodologies for the recovery of gold has increased. In this particular research, the use of cone hops biomass (Humulus lupulus) was investigated as a new option for gold recovery. The results showed that the gold binding to native hops biomass was pH dependent from pH 2 to pH 6, with a maximum percentage binding at pH 3. Time dependency studies demonstrated that Au(III) binding to native and modified cone hops biomasses was found to be time independent at pH 2 while at pH 5, it was time dependent. Capacity experiments demonstrated that at pH 2, esterified hops biomass bound 33.4 mg Au/g of biomass, while native and hydrolyzed hops biomasses bound 28.2 and 12.0 mg Au/g of biomass, respectively. However, at pH 5 the binding capacities were 38.9, 37.8 and 11.4 mg of Au per gram of native, esterified and hydrolyzed hops biomasses, respectively.

We report on energetic surface reconstruction phenomena observed on bimetallic nanoparticle systems of AuPd and AuCu, similar to a resolidification effect observed during the cooling process in lead clusters. These binary alloy nanoparticles show the fivefold edges truncated, resulting in { 100 } facets on decahedral structures, an effect largely envisioned and reported theoretically, with no experimental evidence so far. We demonstrate experimentally as well as by computational simulations that this new eutectic structure is favored in such nanoalloy systems. Fil: Rodríguez López J. L.. Instituto Potosino de Investigación Científica y Tecnológica ; México Fil: Montejano Carrizales, J. M.. Universidad Autónoma de San Luis Potosí; México Fil: Pal, U.. Universidad Auto´noma de Puebla; México Fil: Sánchez Ramírez, J. F.. Universidad Auto´noma de Puebla; México Fil: Troiani, Horacio Esteban. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina Fil: García, D.. The University of Texas; Estados Unidos Fil: Miki Yoshida, M.. The University of Texas; Estados Unidos Fil: José Yacamán, Miguel. The University of Texas; Estados Unidos

The synthesis method for obtaining sub-micrometric structures of rare earth manganese-based mixed oxide compounds is described. Pore wetting of porous polycarbonate templates with the liquid precursor was followed by a two-stage thermal treatment to obtain single phase La0.325Pr0.300Ca0.375MnO3 hollow and solid structures, with external diameter determined by the sacrificial template pore size. The first thermal stage, a microwave assisted denitration process, determines the shape of the structures. The second treatment, performed at 1073 K, allows to obtain the crystallographic structure of the compound. A variety of techniques (scanning and transmission electron microscopy, scanning probe microscopy) allowed to fully characterize the microstructure and morphology of these self-standing manganite nanostructures. For 1 mum pore size templates we obtained tubes, with external diameter around 800 nm and wall thickness around 150 nm; densely packed nanoparticles sized 20-50 nm are the building blocks of the walls. For pore size below 0. 1 mum, solid nanowires were obtained, the size of constituent crystallites being around 10 nm. Overall obtained material exhibits ferromagnetic ordering below 200 K.

Starting from an amorphous C film, single-walled carbon nanotubes were obtained in situ in a high-resolution electron microscope by the combined effect of irradiation and axial strain. Ductile nanotubes developed either a junction or a linear chain of C atoms before failure. These facts have been put in direct evidence for the first time. Tight-binding calculations indicate that the bonding in the linear chain is of a cumulene type., This work was supported by the CONYCYT, Argentina, by special funds from Texas Materials Institute and the Center for Nano and Molecular Technology (UT-Austin), CONACYT, México, the University of the Basque Country, DGES, and by the EU research training network NANOPHASE (HPRN-CT-2000-00167).

In this work we describe the synthesis and characterization of maghemite nanoparticles obtained by a new synthetic route. The material was synthesized using triethylamine as a coprecipitation agent in the presence of the organic ligand N , N′ -bis(3,5-di-tert-butyl-catechol)-2,4-diaminotoluene (LCH 3 ). Mossbauer spectrum at 4 K shows typical hyperfine parameters of maghemite and Transmission Electron Microscopy images reveal that the nanoparticles have a mean diameter of 3.9 nm and a narrow size distribution. AC magnetic susceptibility in zero field presents an Arrhenius behavior with unreasonable relaxation parameters due to the strong influence of dipolar interaction. In contrast when the measurements are performed in a 1 kOe field, the effect of dipolar interactions becomes negligible and the obtained parameters are in good agreement with the static magnetic properties. The dynamic energy barrier obtained from the AC susceptibility results is larger than the expected from the average size observed by HRTEM results, evidencing the strong influence of the surface contribution to the anisotropy.

We report a simple and effective way to control the heat generation of a magnetic colloid under alternate magnetic fields by changing the shell composition of bimagnetic core-shell Fe3O4/ZnxCo1-xFe2O4 nanoparticles. The core-shell structure constitutes a magnetically-coupled biphase system, with an effective anisotropy that can be tuned by the substitution of Co2+ by Zn2+ ions in the shell. Magnetic hyperthermia experiments of nanoparticles dispersed in hexane and butter oil showed that the magnetic relaxation is dominated by Brown relaxation mechanism in samples with higher anisotropy (i.e., larger concentration of Co within the shell) yielding high specific power absorption values in low viscosity media as hexane. Increasing the Zn concentration of the shell, diminishes the magnetic anisotropy, which results in a change to a Neel relaxation that dominates the process when the nanoparticles are dispersed in a high-viscosity medium. We demonstrate that tuning the Zn contents at the shell of these exchange-coupled core/shell nanoparticles provides a way to control the magnetic anisotropy without loss of saturation magnetization. This ability is an essential prerequisite for most biomedical applications, where high viscosities and capturing mechanisms are present.