Progress in powder and surface X-ray diffraction crystallography

Una de les fites científiques més importants del segle XX ha estat sens dubte la descoberta de la difracció dels raigs X per la matèria cristal·lina i l'aprofitament d'aquest procés en la determinació de l'estructura cristal·lina dels materials. Tanmateix, no és fins a la darreria de segle que arriba la maduresa en aquest camp amb la solució gairebé automàtica de les estructures cristal·lines petites. Amb la maduresa emergeixen noves aplicacions dels mètodes de difracció. al destacar, entre les més importants per a la Ciència de Materials, la determinació de les estructures cristal·lines a partir de dades provinents de la difracció dels raigs X en pols cristal·lina, així com també la determinació de la disposició atòmica en les superfícies dels substrats i dels corresponents dipòsits, quan n'hi ha. Com que els avenços en aquestes dues aplicacions van estretament lligats a una reinterpretació recent dels mètodes directes tradicionals de solució d'estructures cristal·lines, s'ha cregut convenient fer-ne una breu introducció. Seguidament, es comentaran les modificacions introduïdes en aquests mètodes, per tal de poder tractar les particularitats específiques d'aquestes dues noves aplicacions, i finalment, es descriuran alguns exemples.One of the most important scientific achievements of the XX century has been without any doubt the discovery of X-ray diffraction by crystalline matter and the subsequent use of this process to determine the crystal structures of the materials. This field matured at the end of the century with the almost automated solution of the crystal structures of small compounds, allowing various new applications of X-ray diffraction methods to emerge. Among the most relevant ones for Materials Sciences one may mention the solution of crystal structures from X-ray powder diffraction intensity data or the determination of atomic arrangements in the surfaces of substrates and, eventually, of the corresponding depositions. Since these advances are closely related to a recent reinterpretation of the traditional direct methods of solving crystal structures, a short introduction to them will be given first. Then we deal with the modification of such methods to cope with the particularities of these two applications and, finally, some examples will be described

Nanostructuring surfaces: Deconstruction of the Pt(110)-(1x2) surface by C60

International audienceWhen deposited on metal surfaces, C60 creates nanoholes. Grazing incidence x-ray diffraction reveals a c( 4x 4) reconstruction induced by C60 on Pt 110) -( 1x 2) . While the initial (1x 2) missing row is partially deconstructed, under each fullerene we find double atomic vacancy involving two Pt layers. The resulting interface is deeply modified with a 75% Pt occupancy and regularly distributed double vacancy. The orientation of the molecule is compatible with local surface cm symmetry with a pentagonal ring almost parallel to the surface while hexagonal rings are almost parallel to the (111) facets of the nanohole. The short nearestneighbor C60 distances increase the van der Waals repulsion forces that are minimized by a charge transfer between molecule and substrate involving a large number of C-Pt bonds and a reduction of 6% of the apparent diameter of the C60 molecule

Structural and electrical properties of indium oxide thin films grown by pulsed laser deposition in oxygen ambient

We report results of structural, optical and electrical transport studies of indium oxide (IO) thin films grown by Pulsed Laser Deposition (PLD) under various oxygen gas pressures and using different substrates at 350° C. We find that the morphology and electrical resistivity of these films which are highly transparent changes drastically as Opressure increases into mbar range, irrespective of substrate. A systematic increase in resistivity, coming mainly from a drop in the electron concentration, is observed as oxygen pressure varies from 0.0004 to 1 mbar. This could permit modulation of IO thin–films’ electrical parameters by more than three orders of magnitude suggesting that PLD grown films could be an attractive material for optoelectronic applications.We acknowledge support from grants MAT2012-38213-C02-01 and MAT2012-38213-C02-02, and MAT2015-686760-02-1-P and MAT2015-686760-02-2-P from the Ministerio de Economía y Competividad of Spain. These grants are co-funded by ERDF of European Union. Additional support from Diputación General de Aragón (DGA-CAMRADS) is also acknowledged.Peer Reviewe

The competences assessment in a dual training experience of teachers: differences and similarities between school and university tutors

La colaboración necesaria entre universidad y escuela en la formación inicial de maestros está en el centro de este estudio de caso. Ambos escenarios contribuyen a la construcción de la profesionalidad, la adquisición y desarrollo de las competencias docentes desde misiones institucionales distintas. Con el inicio de una experiencia de formación dual, en un dispositivo pedagógico de integración de aprendizajes, se constatan diferencias entre las evaluaciones de los tutores universitarios y los tutores escolares. Con el interés de explicar estas valoraciones se contrastan en su dimensión global y en relación a la competencia metodológica. Los resultados pueden explicarse principalmente por la diferencia de roles de los tutores: por un lado, desde la socialización profesional en la colaboración en la actividad propiamente escolar (tutores escolares) y, por otro, desde una actividad más propia del análisis, comprensión, relación con los marcos teóricos y reflexión demandados desde la universidad (tutores universitarios).The need for schools and universities to w ork together in the initial training of teachers lies at the centre of this case study. These two institutions help to build professionalism and to promote the acquisition and development of teaching skills through their respective missions. With the start of a dual training experience, within a pedagogic approach based on the integration of different learning styles, we have noted differences between the ways that university tutors and school tutors make evaluations. To explain these evaluations, we have compared and contrasted them at the global scale and with reference to methodological competences. The results obtained can mainly be explained by the different roles that tutors play in these two contexts. In the case of school tutors, this involves professional socialization in collaboration in school-centred activities. In the other case, the activity of university tutors is more closely related to analysis and understanding, theoretical frameworks and acts of reflection

Structural study of decrespignyite-(Y), a complex yttrium rare earth copper carbonate chloride, by three-dimensional electron and synchrotron powder diffraction

The crystal structure of the mineral decrespignyite-(Y) from the Paratoo copper mine (South Australia) has been obtained by applying d recycling direct methods to 3D electron diffraction (ED) data followed by Rietveld refinements of synchrotron data. The unit cell is a = 8.5462(2), c = 22.731(2) Å and V = 1437.8(2) Å3, and the chemical formula for Z = 1 is (Y10.35REE1.43Ca0.52Cu5.31 σ17.61(CO3)14Cl2.21(OH)16.79• 18.35H2O (REE. rare earth elements). The ED data are compatible with the trigonal P 3m1 space group (no. 164) used for the structure solution (due to the disorder affecting part of the structure, the possibility of a monoclinic unit cell cannot completely be ruled out). The structure shows metal layers perpendicular to [001], with six independent positions for Y, REE and Cu (sites M1 to M4 are full, and sites M5 and M6 are partially vacant), and two other sites, Cu1 and Cu2, partially occupied by Cu. One characteristic of decrespignyite is the existence of hexanuclear (octahedral) oxo-hydroxo yttrium clusters [Y6(μ6-O)(μ3-OH)8O24] (site M1) with the 24 bridging O atoms belonging to two sets of symmetry-independent.CO3/2- ions, with the first set (2×) along a ternary axis giving rise to a layer of hexanuclear clusters and the second set (6×) tilted and connecting the hexanuclear clusters with hetero-tetranuclear ones hosting Cu, Y and REE (M2 and M3 sites). The rest of the crystal structure consists of two consecutive M3 C M4 layers containing the partially occupied M5, M6, and Cu2 sites and additional carbonate anions in between. The resulting structure model is compatible with the chemical analysis of the type material which is poorer in Cu and richer in (REE, Y) than the above-described material.Fil: Rius, Jordi. Consejo Superior de Investigaciones Científicas. Instituto de Ciencia de los Materiales de Barcelona; EspañaFil: Colombo, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Vallcorba, Oriol. Alba Synchrotron Light Facility; EspañaFil: Torrelles, Xavier. Consejo Superior de Investigaciones Científicas. Instituto de Ciencia de los Materiales de Barcelona; EspañaFil: Gemmi, Mauro. Istituto Italiano di Tecnologia. Center for Nanotechnology Innovation; ItaliaFil: Mugnaioli, Enrico. Istituto Italiano di Tecnologia. Center for Nanotechnology Innovation; Itali

Three-Dimensional Study of F. graminearum Colonisation of Stored Wheat: Post-Harvest Growth Patterns, Dry Matter Losses and Mycotoxin Contamination

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Fusarium causes significant post-harvest quality losses and mycotoxin contamination instored wheat but the colonisation dynamics of the grain and how this may be affected by the initialinoculum position in the grain mass is poorly understood. This study examined the 3D growthkinetics and mycotoxin production (deoxynivalenol and zearalenone) by F. graminearum duringhyphal colonisation from different initial inoculum positions in wheat microcosms (top-centre,bottom-centre, and bottom-side) maintained at two water activities (aw; 0.95 and 0.97). Clear jarswere used to visually follow the colonisation dynamics. Fungal respiration and associated drymatter loss (DML) and ergosterol were also quantified. Colonisation dynamics was shown to beaffected by the inoculation position. At the end of the colonisation process, fungal respiration andDML were driven by the inoculation position, and the latter also by the prevailing aw. Fungalbiomass (ergosterol) was mainly affected by the aw. The initial inoculum position did not affect therelative mycotoxin production. There was a positive correlation between respiration and ergosterol,and between mycotoxin production and colonisation indicators. We suggest that spatially explicitpredictive models can be used to better understand the colonisation patterns and mycotoxincontamination of stored cereal commodities and to aid more effective post-harvest management.Peer reviewedFinal Published versio

Double-cell superstructure and vacancy ordering in tensile-strained metallic thin films of P r0.50 C a0.50Co O3 on LaAl O3

The Pr-based cobaltate Pr0.5Ca0.5CoO3 (PCCO) presents in bulk form a singular simultaneous valence and spin-state transition that turns the metallic state into insulator, and displays a large and ultrafast photoresponse in the insulating phase. Epitaxial thin films of PCCO have been grown by deposition on LaAlO3(001) (LAO) substrate, chosen to minimize the mismatch with the film. The films grow epitaxially with two times the substrate periodicity (2a0×2a0×2a0) and the long perovskite axis perpendicular to the surface. We report a reduction of the structural symmetry from Pnma (bulk) to P212121 (film). The P212121 symmetry revealed by synchrotron x ray remains at low temperatures. These PCCO films are metallic, and ferromagnetic below TC=170K, confirming the stabilization of excited Co3+ spin states and the suppression of the concurrent Co spin-state, valence, and metal-insulator transitions. Z-contrast imaging and electron-energy-loss spectroscopy elemental maps reveal long-range ordered oxygen vacancy planes unexpectedly stacking parallel to the interface, in spite of the tensile character of the PCCO/LAO heterostructure. In contrast to the general tendency reported for strained La0.5Sr0.5CoO3-d (LSCO) films, we show that a nominal tensile strain can be also compatible with the presence of alternating O vacancy planes parallel to the interface, instead of perpendicular to it. That occurs thanks to the double cell of the film and the formation of the (1/2, 1/2, 1/2) superstructure studied in this work. These results expand the possibilities of controlling interfacial physical properties via engineering of ordered oxygen-defect structures in strongly correlated oxides

Competencia de trabajo en equipo: Definición y categorización

La competencia de trabajo en equipo se impone a la individualización laboral. El cambio de estructura y proceso de las organizaciones de la sociedad actual ha generado un gran impacto en la nueva manera de trabajar. Las tareas han aumentado su dificultad, haciendo que su resolución individual sea imposible. Es por este motivo, que las organizaciones del trabajo reclaman, hoy más que nunca, la competencia transversal de trabajo en equipo. Este constructo (Competencia de Trabajo en Equipo) recientemente nuevo en las organizaciones ofrece definiciones y modelos de categorización subyacentes que necesitan hacerse oír en el panorama sociolaboral. En esta revisión de la literatura se analizan los 4 modelos más representativos de la competencia de trabajo en equipo, a través de los cuales se propone una definición de la competencia y una posible estructura de la categorización de la misma

Teamwork competence: Definition and categorization

The competence of teamwork is imposed to the labor individualization. The change of structureand process of the organizations of the current society has generated a great impact in the newway of working. The tasks have increased its difficulty, doing that individual resolution is impossible. It is for this motive, that the organizations of the work claim, today more than never, the transversal competence of teamwork.This concept (Competence of Teamwork) recently new in the organizations offers definitions andunderlying models of categorization who need to make be heard in the social and labor context. Inthis review of the literature there are analyzed the 4 most representative models of thecompetence, across which one proposes a definition of the competence and a possible structure ofthe categorization of it