Pyrochlore-like ZrO2-PrOx compounds: The role of the processing atmosphere in the stoichiometry, microstructure and oxidation state

The object of this work is to study the relation between composition, microstructure and oxidation state of Pr2±xZr2∓xO7±y materials produced by the laser–floating zone (LFZ) technique. Three compositions are studied, nominally Pr1.7Zr2.3O7+y, Pr2Zr2O7+y and Pr2.24Zr1.76O7±y, all within the pyrochlore field in the ZrO2–PrOx phase diagram. Samples have been processed under four different atmospheres (O2, air, N2 and 5%H2(Ar)), so as to vary the environmental conditions from oxidising to reducing. Sample colouration ranged from dark brown to bright green, owing to varying Pr4+ content. A close correlation is found between the phase homogeneity, the microstructure and the Pr content. Pr–deficient samples present a homogeneous microstructural aspect and composition, whereas Pr–rich compositions always break into 5–25 µm–sized grains with pyrochlore phases at the grain centre and ill–crystallised, Pr–rich oxidised phases at the grain–boundaries. Raman spectroscopy shows that different types of oxygen disorder occur depending on composition and processing atmosphere: in Pr–poor samples oxygen interstitials are created to compensate for Zr4+ excess charge, whereas in Pr–rich samples oxygen disorder occurs around the Pr3+ or Pr4+ ions substituting for Zr4+, because of size–mismatch. Magnetic measurements showed a high Pr4+ content, which has been attributed to several factors: the highly oxidised state of the feedstock material, the segregation of Pr and O–rich grain boundaries in compositions with praseodymium molar rate> 0.5, and the lower oxide–ion conductivity for PZO compositions, compared to either Pr–poor or Pr–rich compositions. Post–processing thermal annealing in a vacuum at 1000 °C enabled total Pr reduction, with the exception of the Pr–rich P2.24 samples, where some Pr4+ ions remained in the oxidised state

The interplay of university and industry through the FP5 network

To improve the quality of life in a modern society it is essential to reduce the distance between basic research and applications, whose crucial roles in shaping today's society prompt us to seek their understanding. Existing studies on this subject, however, have neglected the network character of the interaction between university and industry. Here we use state-of-the-art network theory methods to analyze this interplay in the so-called Framework Programme--an initiative which sets out the priorities for the European Union's research and technological development. In particular we study in the 5th Framework Programme (FP5) the role played by companies and scientific institutions and how they contribute to enhance the relationship between research and industry. Our approach provides quantitative evidence that while firms are size hierarchically organized, universities and research organizations keep the network from falling into pieces, paving the way for an effective knowledge transfer.Comment: 21 pages (including Appendix), 8 figures. Published online at http://stacks.iop.org/1367-2630/9/18

Raman selection rules in uniaxial media: The nonpolar modes of Mn Ga2 Se4

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).It is known that optically anisotropic media can change the polarization of light propagating inside them. As regards Raman spectroscopy, this affects the light intensity measured in different geometrical configurations and results in an apparent unfulfillment of selection rules. We present an experimental and theoretical study of such effects in the defect chalcopyrite semiconductor MnGa2Se4. Optical anisotropy is taken into account by including in the calculation of Raman intensities the phase difference appearing between ordinary and extraordinary waves as they propagate, in uniaxial media, with different velocities. Birefringence can be obtained from Raman measurements provided that the distance run by the light is known.We acknowledge financial support from research project MAT2001-3713-C04.Peer Reviewe

Adaptación y mejora de un dispositivo de filtración de agua de uso doméstico existente para la extracción mediante disolución en el agua de productos solubles contenidos en envoltura hidrosoluble

Número de publicación: ES2397892 A1 (12.03.2013) También publicado como: ES2397892 B1 (16.01.2014) Número de Solicitud: Consulta de Expedientes OEPM (C.E.O.) P201100258 (18.02.2011)El objetivo es proponer un procedimiento y un dispositivo que permitan la extracción de un fertilizante contenido en una envoltura hidrosoluble sin generar residuos provenientes del envase vacío, evitando el contacto con el producto, garantizando la extracción del fertilizante mediante la disolución previa del envoltorio y a una circulación de agua a su través, incorporando un sistema de filtrado final, y facilitando el llenado y limpieza del dispositivo mediante un sistema de apertura y cierre roscado.Universidad de Almerí

New objects in old structures: The Iron Age hoard of the Palacio III megalithic funerary complex (Almadén de la Plata, Seville, Spain)

Cultural contact, exchange and interaction feature high in the list of challenging topics of current research on European Prehistory. Not far off is the issue of the changing role of monuments in the making and maintaining of key cultural devices such as memory and identity. Addressing both these highly-debated issues from a science-based perspective, in this paper we look at an unusual case study set in southern Iberia and illustrate how these archaeological questions can benefit from robust materials-science approaches.We present the contextual, morphological and analytical study of an exceptional Early Iron Age hoard composed of a number of different (and mostly exotic) materials such as amber, quartz, silver and ceramic. This hoard, found under the fallen orthostat of a megalithic structure built at least 2000 years earlier, throws new light on long-distance exchange networks and the effect they could have had on the cultural identities and social relations of local Iberian Early Iron Age communities. Moreover, the archaeometric study reveals how diverse and distant the sources of these item are (Northern Europe to Eastern and Western Mediterranean raw materials, as well as local and eastern technologies), therefore raising questions concerning the social mechanisms used to establish change and resistance in contexts of colonial encounter

Energy dissipation in a nonlinearly damped Duffing oscillator

International audienceIn this paper, we study the effect of including a nonlinear damping term proportional to the power of the velocity in the dynamics of a double-well Duffing oscillator. In particular, we focus our attention in understanding how the energy dissipates over a cycle and along the time, by the use of different tools of analysis. Analytical and numerical results for different damping terms are shown, and the presence of a discontinuity and an inversion of behavior depending on the initial energy are discussed. An averaged power loss in a period is defined, showing similar characteristics as the energy dissipation over a cycle, although no discontinuity is present. The discontinuity gap which appears for the energy dissipation at a certain value of the initial energy decreases as the power of the damping term increases and an associated scaling law is found

Caracterización estructural y espectroscópica de fibras cristalinas de Ce0.4Zr0.6O2 crecidas mediante el método de fusión zonal asistida por láser

[EN] A structural and spectroscopic characterization of crystalline rods of Ce0.4Zr0.6O2 grown by the laser floating zone (LFZ) method is presented. A precursor rod of Ce0.4Zr0.6O2 composition was sintered at 1500 ºC in air atmosphere and then processed by the LFZ technique with a CO2 laser. The processed material was characterized by XRD, SEM and Raman spectroscopy. In the as-grown, dark-color processed rod, the Raman spectrum evolves radially from a t’-like one, corresponding to Ce0.37Zr0.63O2 composition, at the edge of the rod, to a very broad and weak, cubic-like one, at the center. The degree of cerium reduction and oxygen non-stoichiometry were determined through measurements of the electronic Raman spectrum of Ce3+. A strong Ce3+ signal was found at the core of the rod, indicating strong reduction, whereas no Ce3+ signal was detected at the edge. To restore oxygen and Ce4+ content a section of the fiber was reoxidized at 620 ºC for 24 h. A very homogeneous spectrum was found in the reoxidized sample, that was assigned to a t’-phase of composition Ce0.42Zr0.58O2.[ES] Presentamos una caracterización estructural y espectroscópica de fibras cristalinas de Ce0.4Zr0.6O2 crecidas mediante fusión zonal asistida por láser (LFZ). Una barra del material precursor, de composición Ce0.4Zr0.6O2, fue sinterizada a 1500 ºC en atmósfera de aire y después procesada por LFZ con un láser de CO2. El material procesado fue caracterizado por difracción de rayos X, microscopía electrónica de barrido y espectroscopía Raman. En la fibra recién procesada, de color gris oscuro, el espectro Raman varía radialmente desde un espectro de tipo t’, correspondiente a una composición Ce0.37Zr0.63O2, en el borde de la fibra, hasta un espectro muy ensanchado y débil, de aspecto cúbico, en el centro. El grado de reducción del cerio y la no estequiometría del oxígeno se determinaron a través de las medidas del Raman electrónico del Ce3+. La señal de Ce3+ era muy intensa en el centro de la fibra, lo que indica una fuerte reducción, mientras que no se detectó en el borde. Para restablecer el contenido de oxígeno y de Ce4+ una parte de la fibra fue reoxidada a 620 ºC durante 24 h. El espectro de la muestra reoxidada, de color amarillo pálido y muy homogénea, fue asignado a una fase t’ de composición Ce0.42Zr0.58O2.Financial support from Spanish project MAT2004-03070-C05-03 is acknowledged.Peer reviewe