Ionic conductivity of nanocrystalline yttria-stabilized zirconia: Grain boundary and size effects

9 páginas, 6 figuras, 3 tablas.-- PACS number(s): 66.30.H-.-- et al.We report on the effect of grain size on the ionic conductivity of yttria-stabilized zirconia samples synthesized by ball milling. Complex impedance measurements, as a function of temperature and frequency are performed on 10 mol % yttria-stabilized zirconia nanocrystalline samples with grain sizes ranging from 900 to 17 nm. Bulk ionic conductivity decreases dramatically for grain sizes below 100 nm, although its activation energy is essentially independent of grain size. The results are interpreted in terms of a space-charge layer resulting from segregation of mobile oxygen vacancies to the grain-boundary core. The thickness of this space-charge layer formed at the grain boundaries is on the order of 1 nm for large micron-sized grains but extends up to 7 nm when decreasing the grain size down to 17 nm. This gives rise to oxygen vacancies depletion over a large volume fraction of the grain and consequently to a significant decrease in oxide-ion conductivity.We acknowledge financial support by Junta de Comunidades de Castilla-La Mancha through Project No. PAI-05-013, by CAM under Grant No. S2009/MAT-1756 (Phama), by Spanish MICINN through Grants No. MAT2008-06517-C02, No. MAT2008-06542-C04, and No. FIS2009-12964- C05-04, and Consolider Ingenio 2010 under Grant No. CSD2009-00013 (Imagine).Peer reviewe

An approach for distributed rostering by means of Web service technologies

La planificación automática de turnos de trabajo (rostering de aquí en adelante) es un proceso fundamental para la mayoría de empresas. Este proceso les permite gestionar sus recursos de forma eficiente. La mayoría de soluciones de planificación automática trabajan en escenarios centralizados. Este proyecto tiene como meta dar un nuevo enfoque al proceso de planificación automática transformando el entorno centralizado en uno distribuido. La tecnología escogida para esta transformación son los servicios Web. Los servicios Web se han posicionado como una de las tecnologías más importantes y utilizadas, sin embargo la combinación de los procesos de planificación automática con servicios Web no ha sido investigada y estudiada en profundidad. Este nuevo enfoque pretende crear soluciones más ligeras y flexibles para empresas de forma que no tengan que preocuparse de tediosas instalaciones y configuraciones El enfoque distribuido puede proveer numerosos beneficios a ambas partes; permitiría centrar este área tecnológica en un entorno web 2.0. Las compañías de planificación automática se actualizarían convirtiéndose en empresas con gran capacidad de interacción con el resto de elementos de la web 2.0. Al mismo tiempo, la empresa que consume los servicios de rostering no tiene que preocuparse por el mantenimiento y actualizaciones. Los calendarios de turnos de trabajo pueden ser obtenidos en cualquier lugar y en cualquier momento. Esto mejora el valor de la empresa y las relaciones con los empleados. Para el desarrollo del proyecto se han creado diferentes aplicaciones. Estas aplicaciones han sido configuradas de distintas formas para abarcar distintas posibilidades de desarrollo y poder así obtener una visión más amplia de las capacidades y posibilidades del sistema distribuido. Las configuraciones están centradas en el tipo de servicio Web usado (SOAP, REST) y en la seguridad y sus diferentes posibilidades. El proyecto es una prueba de concepto de como este nuevo enfoque funcionaría, resaltando los puntos fuertes y deficiencias de éste; de la misma manera pretende sentar una base para futuros proyectos en este área. El proyecto ha conseguido cumplir con los objetivos propuestos, mostrando los puntos fuertes y débiles del enfoque. De forma sorprendente y contraria a las expectativas los problemas aparecen al obtener los datos necesarios de las diferentes empresas para crear el calendario. En principio, se esperaba que el cuello de botella del sistema se encontrase en el proceso de rostering, ya que normalmente es un proceso costoso y pesado. Los resultados del proyecto muestran como el cuello de botella está localizado cuando se intenta obtener la información de empresas externas. Este problema resalta la característica principal de este nuevo enfoque: es necesario un sistema personalizado para cada empresa que quiera consumir los servicios de rostering. Esto significa que a pesar de tener un sistema global funcionando con servicios Web, no es válido para todas las empresas que quieran utilizarlo y consecuentemente hay que adaptarlo a cada una de ellas. La colaboración entre empresas se vuelve esencial en este nuevo enfoque. Esto complica la idea inicial y cambia los objetivos de las empresas de rostering que necesitan una profunda transformación de sus sistemas y su funcionamiento

X-Ray Magnetic Circular Dichroism at the K edge of Mn3GaC

We theoretically investigate the origin of the x-ray magnetic circular dichroism (XMCD) spectra at the K edges of Mn and Ga in the ferromagnetic phase of Mn3GaC on the basis of an ab initio calculation. Taking account of the spin-orbit interaction in the LDA scheme, we obtain the XMCD spectra in excellent agreement with the recent experiment. We have analyzed the origin of each structure, and thus elucidated the mechanism of inducing the orbital polarization in the p symmetric states. We also discuss a simple sum rule connecting the XMCD spectra with the orbital moment in the p symmetric states.Comment: 5 pages, 5 figures, accepted for publication in Physical Review

Magnetic circular dichroism of x-ray absorption spectroscopy at rare-earth L2,3 edges in RE2Fe14B compounds (RE = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)

Magnetic circular dichroism (MCD) in the x-ray absorption spectroscopy (XAS) at the L2,3 edges for almost entire series of rare-earth (RE) elements in RE2Fe14B, is studied experimentally and theoretically. By a quantitative comparison of the complicated MCD spectral shapes, we find that (i) the 4f-5d intra-atomic exchange interaction not only induces the spin and orbital polarization of the 5d states, which is vital for the MCD spectra of the electric dipole transition from the 2p core states to the empty 5d conduction band, but also it accompanies a contraction of the radial part of the 5d wave function depending on its spin and orbital state, which results in the enhancement of the 2p-5d dipole matrix element, (ii) there are cases where the spin polarization of the 5d states due to the hybridization with the spin polarized 3d states of surrounding irons plays important roles, and (iii) the electric quadrupole transition from the 2p core states to the magnetic vale! nce 4f states is appreciable at the pre-edge region of the dipole spectrum. Especially, our results evidence that it is important to include the enhancement effect of the dipole matrix element in the correct interpretation of the MCD spectra at the RE L2,3 edges.Comment: 9 pages, 5 figures, 1 table, REVTe

Ab initio x-ray absorption study of copper K -edge XANES spectra in Cu(II) compounds

This work reports a theoretical study of the x-ray absorption near-edge structure spectra at the Cu K edge in several Cu(II) complexes with N -coordinating ligands showing a square-planar arrangement around metal cation. It is shown that single-channel multiple-scattering calculations are not able to reproduce the experimental spectra. The comparison between experimental data and ab initio computations indicates the need of including the contribution of two electronic configurations (3 d9 and 3 d10 L) to account for a proper description of the final state during the photoabsorption process. The best agreement between theory and experiment is obtained by considering a relative weight of 68% and 32% for the two absorption channels 3 d10 L and 3 d9, respectivelyComisión Interministerial de Ciencia y Tecnología MAT2002-04178-C04-03, BQU2002-02217 y BQU2002- 04364-C02-0

Role of the exchange and correlation potential into calculating the x-ray absorption spectra of half-metallic alloys: the case of Mn and Cu K-edge XANES in Cu2_2MnM (M = Al, Sn, In) Heusler alloys

This work reports a theoretical study of the x-ray absorption near-edge structure spectra at both the Cu and the Mn K-edge in several Cu$_2$MnM (M= Al, Sn and In) Heusler alloys. Our results show that {\it ab-initio} single-channel multiple-scattering calculations are able of reproducing the experimental spectra. Moreover, an extensive discussion is presented concerning the role of the final state potential needed to reproduce the experimental data of these half-metallic alloys. In particular, the effects of the cluster-size and of the exchange and correlation potential needed in reproducing all the experimental XANES features are discussed.Comment: 15 pages, 5 figure

X-ray magnetic circular dichroism measurements using an X-ray phase retarder on the BM25 A-SpLine beamline at the ESRF

6 páginas, 8 figuras.Circularly polarized X-rays produced by a diamond X-ray phase retarder of thickness 0.5 mm in the Laue transmission configuration have been used for recording X-ray magnetic circular dichroism (XMCD) on the bending-magnet beamline BM25A (SpLine) at the ESRF. Field reversal and helicity reversal techniques have been used to carry out the measurements. The performance of the experimental set-up has been demonstrated by recording XMCD in the energy range from 7 to 11 keV.This work was partially supported by a Spanish CICYTMAT2008- 06542-C04 grant. MALM and RB acknowledge the Ministerio de Ciencia e Innovación of Spain for their Postdoctoral and PhD grants, respectively. We also acknowledge the Spanish Ministerio de Ciencia e Innovación and Consejo Superior de Investigaciones Científicas for financial support.Peer reviewe

X-ray absorption study of the local structure at the NiO/oxide interfaces

This work reports an X-ray absorption near-edge structure (XANES) spectroscopy study at the Ni K-edge in the early stages of growth of NiO on non-ordered SiO2, Al2O3 and MgO thin films substrates. Two different coverages of NiO on the substrates have been studied. The analysis of the XANES region shows that for high coverages (80 Eq-ML) the spectra are similar to that of bulk NiO, being identical for all substrates. In contrast, for low coverages (1 Eq-ML) the spectra differ from that of large coverages indicating that the local order around Ni is limited to the first two coordination shells. In addition, the results also suggest the formation of cross-linking bonds Ni - O - M (M = Si, Al, Mg) at the interfaceThis work was partially supported by the Spanish CONSOLIDER Project FUNCOAT CSD2008-00023, the ENE2010-21198-C04-04 and MAT2011-27573-C04-04 projects and by the Aragón DGA NETOSHIMA grant. We acknowledge the Spanish Ministerio de Ciencia e Innovación and CSIC for financial support and for provision of synchrotron radiation and we would like to thank the staff of SpLine at ESRF and KMC2 at BESSY II for technical support. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 2267

Microstructural and magnetic characterization of Fe- and Ir-based multilayers

Nominal [Fe(t)/Ir(t′)]n (M/M type), [FeOx(t)/IrOx(t′)]n (O/O), and [Fe(t)/IrOx(t′)]n (M/O) multilayers have been prepared by magnetron sputtering at room temperature. Composition, structure, and magnetic behavior have been analyzed. In the M/M samples, the Fe and Ir phases are identified as bcc and fcc, respectively. The magnetism evolves from bulklike iron to granular behavior as the thickness of the Fe layers decreases. An induced magnetic moment, ferromagnetically coupled to Fe, is observed on Ir by x-ray magnetic circular dichroism (XMCD). Besides, the presence of negative remanent magnetization is observed in the M/M samples. As for the M/O samples, the stronger affinity of iron for oxygen displaces the oxygen atoms giving rise to actual heterostructures that strongly differ from the nominal ones. For similar thickness of the two layers the Fe layer become oxidized while a mixture of metal and oxide phases is found in the Ir layer. The increase of the Fe thickness leads to a metallic Ir layer and a highly coercive (∼4.4 kOe) core-shell metal-oxide structure in the Fe layers.Spanish Ministry of Economy and Competitiveness (MINECO), MAT2014-54425-R, MAT2017-83468-RAragón DGA NETOSHIM

Microstructural and magnetic characterization of Fe- and Ir-based multilayers

Nominal [Fe(t)/Ir(t'')](n) (M/Mtype), [FeOx(t)/IrOx(t'')](n) (O/O), and [Fe(t)/IrOx(t'')](n) (M/O) multilayers have been prepared by magnetron sputtering at room temperature. Composition, structure, and magnetic behavior have been analyzed. In the M/M samples, the Fe and Ir phases are identified as bcc and fcc, respectively. The magnetism evolves from bulklike iron to granular behavior as the thickness of the Fe layers decreases. An induced magnetic moment, ferromagnetically coupled to Fe, is observed on Ir by x-ray magnetic circular dichroism (XMCD). Besides, the presence of negative remanent magnetization is observed in the M/M samples. As for the M/O samples, the stronger affinity of iron for oxygen displaces the oxygen atoms giving rise to actual heterostructures that strongly differ from the nominal ones. For similar thickness of the two layers the Fe layer become oxidized while a mixture of metal and oxide phases is found in the Ir layer. The increase of the Fe thickness leads to a metallic Ir layer and a highly coercive (similar to 4.4 kOe) core-shell metal-oxide structure in the Fe layers