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Moure C.,CSIC - Institute of Ceramics and Glass | Pena O.,CNRS Chemistry Institute of Rennes
Progress in Solid State Chemistry | Year: 2015

The perovskite structure is one of the most wonderful to exist in nature. It obeys to a quite simple chemical formula, ABX3, in which A and B are metallic cations and X, an anion, usually oxygen. The anion packing is rather compact and leaves interstices for large A and small B cations. The A cation can be mono, di or trivalent, whereas B can be a di, tri, tetra, penta or hexavalent cation. This gives an extraordinary possibility of different combinations and partial or total substitutions, resulting in an incredible large number of compounds. Their physical and chemical properties strongly depend on the nature and oxidation states of cations, on the anionic and cationic stoichiometry, on the crystalline structure and elaboration techniques, etc. In this work, we review the different and most usual crystalline representations of perovskites, from high (cubic) to low (triclinic) symmetries, some well-known preparation methods, insisting for instance, in quite novel and original techniques such as the mechanosynthesis processing. Physical properties are reviewed, emphasizing the electrical (proton, ionic or mixed conductors) and catalytic properties of Mn- and Co-based perovskites; a thorough view on the ferroelectric properties is presented, including piezoelectricity, thermistors or pyroelectric characteristics, just to mention some of them; relaxors, microwave and optical features are also discussed, to end up with magnetism, superconductivity and multiferroïsme. Some materials discussed herein have already accomplished their way but others have promising horizons in both fundamental and applied research. To our knowledge, no much work exists to relate the crystalline nature of the different perovskite-type compounds with their properties and synthesis procedures, in particular with the most recent and newest processes such as the mechanosynthesis approach. Although this is not intended to be a full review of all existing perovskite materials, this report offers a good compilation of the main compounds, their structure and microstructure, processing and relationships between these features. © 2015 Elsevier Ltd. All rights reserved.

Lee Y.,Brown University | Garcia M.A.,CSIC - Institute of Ceramics and Glass | Frey Huls N.A.,Brown University | Sun S.,Brown University
Angewandte Chemie - International Edition | Year: 2010

("Figure Presented") Dumbbell-like Au-Fe3O4 nanoparticles and their single-component counterparts, Au and Fe 3O4, were compared regarding their H2O 2 reduction capability. The Au-Fe3O4 nanoparticles are catalytically more active, which is attributed to polarization effects from Au to Fe3O4. This activity can be further tuned by the size of the nanoparticles. © 2010 Wiley-VCH Verlag GmbH &. Co. KGaA,.

Garcia M.A.,CSIC - Institute of Ceramics and Glass | Garcia M.A.,IMDEA Madrid Institute for Advanced Studies
Journal of Physics D: Applied Physics | Year: 2011

The excitation of surface plasmons (SPs) in metallic nanoparticles (NPs) induces optical properties hardly achievable in other optical materials, yielding a wide range of applications in many fields. This review presents an overview of SPs in metallic NPs. The concept of SPs in NPs is qualitatively described using a comparison with simple linear oscillators. The mathematical models to carry on calculations on SPs are presented as well as the most common approximations. The different parameters governing the features of SPs and their effect on the optical properties of the materials are reviewed. Finally, applications of SPs in different fields such as biomedicine, energy, environment protection and information technology are revised. © 2011 IOP Publishing Ltd.

Moreno R.,CSIC - Institute of Ceramics and Glass
Advances in Applied Ceramics | Year: 2012

Colloidal processing has demonstrated its suitability to produce complex shaped ceramics and ceramic-metal composites with tailored microstructure. By combining different shaping methods, it is possible to produce complex three-dimensional bodies as well as single or multilayer coatings, self-sustaining films and laminates. This work summarises the main features of colloidal processing, including colloidal stability and stabilisingmechanisms focusing the importance of the rheological behaviour in the shaping step. The most common shapingmethods and consolidationmechanisms based on suspensions are presented as well as their capabilities for producing composites with complex shapes and microstructures. © 2012 Institute of Materials.

Tande C.,CSIC - Institute of Ceramics and Glass | Perez-Coll D.,CSIC - Institute of Ceramics and Glass | Mather G.C.,CSIC - Institute of Ceramics and Glass
Journal of Materials Chemistry | Year: 2012

Ionic transport in nanocrystalline solid oxides is of considerable current interest. Several studies have reported room-temperature proton conductivity in nanoscaled 8 mol% Y 2O 3-doped zirconia (YSZ), although the location of the transport species is not clear. In this study, nanocrystalline YSZ with a grain size of ∼50 nm was prepared by spark-plasma sintering of nanoscaled commercial powder to a density of >97% of the theoretical value. Impedance spectroscopy was employed to analyze the electrical behavior in the temperature range 25-600 °C in H 2O- and D 2O-wetted atmospheres (air, O 2 and 10% H 2:90% N 2). Transport in wet conditions below 50 °C is limited to the sample surface and occurs via proton hopping (Grötthus mechanism), as demonstrated by a conductive H +/D + isotope effect. The impedance in these conditions is dominated by a single arc which can be modelled with parallel paths for proton transport on the lateral sample surface and a capacitance with values of the order of those of the grain interior. Surface proton transport is considerable, exhibiting a resistance at 26 °C in wet atmospheres comparable to that obtained at ∼300 °C. In contrast, transport by volumetric processes (grain, grain boundary or nanopores) was demonstrated to be insignificant by experiments involving conductivity measurements with a coated lateral surface, with electrode configurations of different areas, and emf measurements in a water-vapour concentration cell. © 2012 The Royal Society of Chemistry.

Carrodeguas R.G.,CSIC - Institute of Ceramics and Glass | De Aza S.,CSIC - Institute of Ceramics and Glass
Acta Biomaterialia | Year: 2011

Nowadays, α-tricalcium phosphate (α-TCP, α-Ca 3(PO 4) 2) is receiving growing attention as a raw material for several injectable hydraulic bone cements, biodegradable bioceramics and composites for bone repair. In the phase equilibrium diagram of the CaO-P 2O 5 system, three polymorphs corresponding to the composition Ca 3(PO 4) 2 are recognized: β-TCP, α-TCP and α′-TCP. α-TCP is formed by heating the low-temperature polymorph β-TCP or by thermal crystallization of amorphous precursors with the proper composition above the transformation temperature. The α-TCP phase may be retained at room temperature in a metastable state, and its range of stability is strongly influenced by ionic substitutions. It is as biocompatible as β-TCP, but more soluble, and hydrolyses rapidly to calcium-deficient hydroxyapatite, which makes α-TCP a useful component for preparing self-setting osteotransductive bone cements and biodegradable bioceramics and composites for bone repairing. The literature published on the synthesis and properties of α-TCP is sometimes contradictory, and therefore this article focuses on reviewing and critically discussing the synthetic methods and physicochemical and biological properties of α-TCP-based biomaterials (excluding α-TCP-based bone cements). © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Perez-Coll D.,CSIC - Institute of Ceramics and Glass | Mather G.C.,CSIC - Institute of Ceramics and Glass
Solid State Ionics | Year: 2010

Dense nanocrystalline Ce0.9Gd0.1O2 - δ (nCGO) with a median grain size of ∼ 120 nm was prepared by spark-plasma sintering of nanoscaled powders. The electrical behaviour of nCGO was analysed by impedance spectroscopy and compared with the micro-grained material of the same composition in humidified (H2O or D2O) and dry O2 in the temperature range 25-600 °C. The large volume of grain boundaries in the nanometric material is highly blocking to oxide-ions, the majority charge carriers above 100 °C, such that the impedance response in this range is dominated by the grain-boundary contribution. The much smaller grain-boundary resistance of micrometric CGO is attributable to the larger grain size rather than a different grain-boundary thickness or conductivity. Proton transport dominates the electrical conductivity of nCGO in wet atmospheres below 100 °C, as demonstrated by the presence of a conductive H+/D+ isotope effect. The absence of a measurable electromotive force in a water-based concentration cell with nCGO as separating membrane and a massively higher resistivity of nCGO samples with a blocked lateral surface both strongly indicate that the proton transport is attributable to surface processes associated with chemisorbed and physisorbed water layers rather than grain-bulk or grain-boundary phenomena. The magnitude of the room-temperature surface proton conductivity is 4-5 times greater for nanostructured Ce0.9Gd0.1O2 - δ than the micrometric analogue. © 2009 Elsevier B.V. All rights reserved.

De Pablos-Martin A.,CSIC - Institute of Ceramics and Glass | Duran A.,CSIC - Institute of Ceramics and Glass | Pascual M.J.,CSIC - Institute of Ceramics and Glass
International Materials Reviews | Year: 2012

Rare earth (RE) doped oxyfluoride glass ceramics possess interesting optical properties with applications in telecommunications and optoelectronics, such as solid state lasers, optical amplifiers, etc. These materials combine the transparency and mechanical and chemical resistance of aluminosilicate glasses with the low phonon energy and facile incorporation of RE ions in the fluoride crystals. The incorporation of RE ions in the crystalline phases enhances the laser emission intensity, a major property of these materials. Transparency is achieved when crystal size is in the nanometric scale, usually below 40 nm, which avoids light scattering. A strict control of the nucleation and crystal growth processes is therefore necessary which requires a deep knowledge of the crystallisation mechanisms. The great activity and publications in this field in the last decades merit a review providing a comparative study of the different nanoglass ceramic systems, their structural and optical characterisation and their main properties and applications. This is the objective of this review paper which includes 227 references. A general discussion on glass nucleation and crystallisation theories and more relevant crystallisation parameters and characterisation techniques are put forward in the first section of the review, focused on nanocrystallisation processes in oxyfluoride systems. In the second section, the principal RE doped glass ceramics are presented. After a general introduction about the luminescence processes, including up- and down-conversion, the behaviour of RE elements in glasses and crystals are discussed. Glass ceramic compositions have been divided as follows: glass ceramics with a glass composition following Wang and Ohwaki's oxyfluoride glass ceramic, and glass ceramics with different matrix compositions, arranged by crystalline phases. Relevant properties, mainly optical and laser, are described in each system along with the most relevant applications of these materials. © 2012 Institute of Materials, Minerals and Mining and ASM International.

Ferrari B.,CSIC - Institute of Ceramics and Glass | Moreno R.,CSIC - Institute of Ceramics and Glass
Journal of the European Ceramic Society | Year: 2010

The colloidal approach has been studied as an essential step in the tailoring of ceramic nanostructures, but most colloidal processes are limited by the complexity of preparation of highly concentrated and stable suspensions of nanoparticles and their fast ageing. Electrophoretic deposition (EPD) stands out as the most appropriate colloidal process to produce ceramic structures using low solid content sols and suspensions (<1 g/l). This characteristic drastically increases its range of technological applicability to nanoparticle assembly, becoming an alternative to the evaporative coating processes. Modelling of this direct electrically driven assembly process is key for its application to the performance of new materials on length scales of approximately 1-100 nm. In this paper, the key contributions in this field to process control and development of the electrophoretic kinetics equation are summarised. © 2009 Elsevier Ltd. All rights reserved.

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