Ceramics with photonic and optical applications

There is a fast growing interest in new applications for advanced ceramic systems in the field of functional materials and in particular for optical materials. Ceramics are entitled to fulfil the gap between glasses and single crystals in the area of photonic materials. The processing versatility and unpaired resistance to high temperature corrosive environments of some ceramics make them good candidates for such applications. However, the critical dependence of the material optical properties on microstructure makes the deep understanding of the processing conditions even more necessary than before for the fabrication of well ordered, transparent, efficient optical ceramics. This review is directed towards ceramists interested in new applications. In the paper we address some fundamental aspects of the relationship between processing, microstructure and optical properties that are illustrated with some examples related with transparent ceramics, glass ceramics, luminescence, random lasers, thermo-emissive applications, scintillators and dielectric metamaterials

Apatite germanates doped with tungsten: Synthesis, structure, and conductivity

et al.High oxygen content apatite germanates, La10Ge 6-xWxO27+x, have been prepared by doping on the Ge site with W. In addition to increasing the oxygen content, this doping strategy is shown to result in stabilisation of the hexagonal lattice, and yield high conductivities. Structural studies of La10Ge 5.5W0.5O27.5 show that the interstitial oxygen sites are associated to a different degree with the Ge/WO4 tetrahedra, leading to five coordinate Ge/W and significant disorder for the oxygen sites associated with these units. Raman spectroscopy studies suggest that in the case of the WO5 units, the interstitial oxygen is more tightly bonded and therefore not as mobile as in the case of the GeO5 units, thus not contributing significantly to the conduction process. © 2011 The Royal Society of Chemistry.Financial support from Spanish project MAT2007-64486-C07-02 is acknowledged.Peer Reviewe

Compositionally graded YSZ–NiO composites by surface laser melting

El pdf del artículo es la versión post-print.Laser surface melting has been applied to near eutectic NiO–YSZ sintered ceramics. The objective is to generate a functional gradient composite material with graded microstructure and composition. At low solidification rates the resultant material has a graded composition, with a severe NiO segregation towards the surface. A thick NiO layer whose thickness depends on the travelling speed is formed. Below this layer the microstructure is eutectic like with composition varying with depth. In contact with the ceramic, excess YSZ coming from the hypereutectic composition forms an almost continuous YSZ layer. The thickness of both segregated layers, NiO and YSZ can be controlled by traverse speed. Thickness decreases as travelling speed increases until a limiting travelling rate of 110 mm/h, at which no more segregation is found. Possible causes to explain the relevant NiO segregation towards the surface are discussed.Financial support from the Ministerio de Educación y Ciencia of Spain and the CE program FEDER under grant MAT2006-13005-C03-01 is gratefully acknowledged.Peer Reviewe

Anode supported microtubular solid oxide fuel cells running on methane

Trabajo presentado al "III Iberian Symposium on Hydrogen, Fuel Cells and Advanced Batteries" celebrado en Zaragoza (España) del 27 al 30 de Junio de 2011.We would like to thank grants MAT2009-14324-C0.2-01 and CIT-120000-2007-50 financed by the Spanish Government and Feder program of the European Community for funding project. M. A. Laguna-Bercero would also like to thank the JAEprogram (CSIC) for financial support.Peer Reviewe

Directionally solidified Al2O3-Yb3Al5O12 eutectics for selective emitters

Al2O3-Yb3Al5O12 eutectic rods were directionally solidified using the laser floating zone method at rates between 25 and 750 mm/h. The microstructure consisted of an interpenetrated network of both eutectic phases for all the growth rates. The size of the phases was strongly dependent on the growth rate, the eutectic interspacing decreasing from 4.5 µm at the lowest growth rate to 600 nm at 750 mm/h. The optical transmission of the sample with coarser microstructure was measured and compared with that of an Yb3Al5O12 single crystal grown "ad hoc" using the same method. The apparent "oscillator strength" of the single 2F7/2¿2F5/2 Yb3+ absorption band was larger in the eutectic sample than in the single crystal, which was attributed to the increase in the light path caused by multiple refractions at the eutectic interphases. The thermal emission of the eutectic rod was studied between 1000 °C and 1500 °C. An intense and relatively narrow emission band at about 1 µm corresponding to the 2F5/2¿2F7/2 Yb3+ electronic transition was observed in the whole temperature range. The intensity of the band increased with the temperature up to about 1300 °C. At higher temperatures a saturation of the selective emission was observed which was attributed to the competition between the increase in the thermal population of the excited state and the enhancement of the non-radiative de-excitation channels with the temperature

Interstitial oxide ion distribution and transport mechanism in aluminum-doped neodymium silicate apatite electrolytes

et al.Rare earth silicate apatites are one-dimensional channel structures that show potential as electrolytes for solid oxide fuel cells (SOFC) due to their high ionic conductivity at intermediate temperatures (500-700 °C). This advantageous property can be attributed to the presence of both interstitial oxygen and cation vacancies, that create diffusion paths which computational studies suggest are less tortuous and have lower activation energies for migration than in stoichiometric compounds. In this work, neutron diffraction of NdAlSiO (0 ≤ x ≤ 1.5) single crystals identified the locations of oxygen interstitials, and allowed the deduction of a dual-path conduction mechanism that is a natural extension of the single-path sinusoidal channel trajectory arrived at through computation. This discovery provides the most thorough understanding of the O transport mechanism along the channels to date, clarifies the mode of interchannel motion, and presents a complete picture of O percolation through apatite. Previously reported crystallographic and conductivity measurements are re-examined in the light of these new findings.We are pleased to acknowledge the Agency for Science, Technology and Research (A*STAR) PSF grant 082 101 0021 “Optimization of Oxygen Sublattices in Solid Oxide Fuel Cell Apatite Electrolytes” for funding the work and the Ministry of Education (MOE) Tier 2 grant T208B1212 for enabling the purchase of a single crystal X-ray diffractometer.Peer Reviewe

Procedimiento de preparación y materiales conformados basados en compuestos eutécticos binarios o ternarios de circonia

Referencia OEPM: P9600891.-- Fecha de solicitud: 19/04/1996.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Procedimiento de preparación y materiales conformados basados en compuestos eutécticos binarios o ternarios de circonia. La presente invención está relacionada con la preparación de materiales con estructuras eutécticas micrométricas basados en mezclas de óxidos, conformados con dimensiones mili y submilimétricas mediante fusión zonal por láser con diferentes sistemas ópticos de focalización y control de los haces de los láseres. Su utilización es en el sector de la producción y conservación de energía, como elementos calefactores, refractarios, cátodos para plasmas de aire, electrodos, en componentes para celdas de combustión, microsensores de gas oxígeno, etc.Peer reviewe

Fabrication and microstructure of self-supporting thin ceramic electrolytes prepared by laser machining

Self-supporting thin Yttria Stabilized Zirconia (YSZ) ceramics electrolytes have been prepared by laser machining. They are carved from a sintered YSZ plate to shape a 20 µm thick and 8 mm in diameter central region, surrounded by an unprocessed 150 µm thick supporting zone. Scanning Electron Microscopy (SEM) and Electron BackScattering Diffraction (EBSD) studies confirmed that the strains produced by the laser processing are small and limited to only one or two layers of YSZ grains (~5 µm). SEM and Transmission Electron Microscopy (TEM) have been also used to characterize the surface of the membrane. It is corrugated and coated with YSZ nanoparticles as a result of the laser plasma deposition. Electrochemical characterization by Impedance Spectroscopy (EIS) showed that this surface morphology improves the electrical performance of the membrane slightly but clearly, reducing the cathode polarization resistance by about 5% in the 650-850 ºC range.This study was funded by the MAT2012-30763 project, which is financed by the Spanish Government (Ministerio de Economía y Competitividad) and the Feder program of the European Union.Peer Reviewe

Laser-assisted surface melting of Al2O3-YSZ eutectic ceramics

[ES] Se presenta un procedimiento para la densificación y/o texturado superficial de cerámicas de Al2O3-YSZ (circona estabilizada con itria) con composición eutéctica mediante fusión zonal asistida por láser. Haciendo un barrido con la radiación proveniente de un láser de potencia sobre piezas cerámicas conseguimos modificar la microestructura y densificar completatmente la capa superficial, con un espesor que va de 30 a 1000 μm. Por ejemplo, con línea estrecha de láser de diodo, fluencia de 1.23 kW/cm2 y velocidades de barrido de 0.14 mm/s, solidificamos capas de 560 μm. El resultado es una superficie de baja rugosidad y no porosa. La microestructura de la muestra es fina debido a su composición eutéctica. La interfase sólido-líquido en el proceso de crecimiento determina la orientación de la microestructura. Se estudia la forma de esta interfase tanto en cortes transversales como longitudinales, lo que permite analizar el efecto que sobre la microestructura tiene la superposición de barridos, que es una alternativa para tratar superficies extensas. Macroscópicamente la frontera entre barridos contiguos es suave. Sin embargo, su microestructura presenta discontinuidad en el espaciado entre las fases debido a la evolución microestructural en la región no fundida sometida a altas temperaturas y a la nucleación preferencial de Al2O3 al comenzar el crecimiento cristalino. Se analizan distintas posibilidades para disminuir el choque térmico inherente al proceso y que conduce a la formación de grietas paralelas a la dirección de procesado y de delaminación. Se observa una mejora importante cuando se precalienta la pieza a tratar, de modo que es posible procesar superficies de cerámicas eutécticas 99% densas.[EN] A procedure for surface densification and/or texturing of Al2O3-YSZ (yttria stabilised zirconia) ceramics with eutectic composition by means of laser surface melting is presented. By scanning a high-power laser beam on a ceramic surface, we achieve a textured and fully dense surface layer from 30 to 1000 microns thick. For example, using a thin diode laser line with fluence 1.23 kW/cm2 and 0.14 mm/s scan rate, the solidified layer has 560 μm depth. We get a low roughness and dense surface. The microstructure is fine (micron size) due to the eutectic composition. The orientation of the microstructure is determined by the shape of the solid-liquid interface in the solidification process. We study the shape of this interface in transverse and longitudinal cross-sections in single as well as overlapping scans, which are required to process large surfaces. From the macroscopic point of view, the transition between adjacent scans is smooth. However, the microstructure presents discontinuity in the interphase spacing due to microstructural evolution in the heat affected region as well as the nucleation of an Al2O3 layer at the beginning of the crystal growth. The thermal shock inherent to the procedure generates cracks longitudinal and transverse to the scanning direction, as well as delaminating cracks. We analyse different possibilities to reduce this thermal shock. The best results are obtained by preheating the substrate, allowing us to process surfaces of Al2O3-YSZ eutectic ceramics 99% dense.Financiación del Ministerio de Ciencia y Tecnología a través de los proyectos MAT2000-1495 y MAT2000-1533-C03-02.Peer reviewe

Mechanical properties of highly textured porous Ni-YSZ and Co-YSZ cermets produced from directionally solidified eutectics

It is well known that several ceramic materials develop an usual; and sometimes unique; combination of properties as a result of mixing different phases with similar expansion coefficients. Sometimes they are elastically stiff, have low thermal expansion coefficients, and are resistant to chemical attack. As this paper will show, their mechanical properties are also enhanced. Nanoindentation is used to measure the mechanical properties for each phase of NiO-YSZ and CoO-YSZ eutectics produced by the laser floating zone technique, and also the analogues Ni-YSZ and Co-YSZ cermets produced by reduction from the eutectic precursors. The different tests have been performed at 100 nm, in order to obtain an imprint lower than the size of the secondary phase and extract the hardness and Young's modulus. Moreover, several tests have been performed at 2000 nm of indentation range to obtain the response of each material. The different imprints have been visualized by Atomic Force Microscopy