Synthesis of ferroelectric perovskites through aqueous-solution techniques

The hydrolysis of niobates in aqueous solutions has been applied to the coprecipitation of PbNb2/3Mg1/303 leading to a low temperature synthesis of this ferroelectric relaxor ceramic. The effect of hydrolysis conditions - such as the concentration of bases and acids used, their rates of addition and the nature of the precursors salts - is described. The perovskite phase appears after heating at 350°C and is obtained as a pure phase at 800°C after heat treatment for 1 h. Relaxor ferroelectric ceramics with a high dielectric constant can be obtained by sintering at 1000°C The process has been also applied to the synthesis of other relaxor ceramic compositions such as PZN (PbNb2/3Zn1/303) and PFN (PbNb1/2Fe1/203) compounds

Thin films of calcium phosphate and titanium dioxide by a sol-gel route: a new method for coating medical implants

Titanium is a commonly used biomaterial for dental and orthopaedic applications. To increase its ability to bond with bone, some attempts were made to coat its surface with calcium phosphate (CaP). This paper describes a new type of coating. Instead of a pure CaP layer, a mixing of titanium dioxide (TiO2) and CaP is fabricated and deposited as a coating. These layers are deposited by a sol-gel route on pure titanium substrates using various pre-treatments. The method consists of mixing a solution of tetrabutyl ortho-titanate or a sol of titanium dioxide with a solution of calcium nitrate and phosphorous esters. This composite is deposited on to commercially pure titanium plates, mechanically polished or blasted with pure crystalline aluminum oxide, using the spin-coating technique. These coatings are then fired at 650 or 850°C for various times. The samples are characterized by X-ray diffraction for their crystallinity, X-ray photoelectron spectroscopy for their surface chemical composition and scanning electron microscopy for their topography. Samples treated at 850°C present a well-pronounced crystallinity, and a high chemical purity at the surface. The topography is strongly related to the viscosity of the precursor and the substrate pre-treatment. Possibilities to structure the outermost layer are presented. © 1999 Kluwer Academic Publisher

A Roadmap for Transforming Research to Invent the Batteries of the Future Designed within the European Large Scale Research Initiative BATTERY 2030+

This roadmap presents the transformational research ideas proposed by “BATTERY 2030+,” the European large-scale research initiative for future battery chemistries. A “chemistry-neutral” roadmap to advance battery research, particularly at low technology readiness levels, is outlined, with a time horizon of more than ten years. The roadmap is centered around six themes: 1) accelerated materials discovery platform, 2) battery interface genome, with the integration of smart functionalities such as 3) sensing and 4) self-healing processes. Beyond chemistry related aspects also include crosscutting research regarding 5) manufacturability and 6) recyclability. This roadmap should be seen as an enabling complement to the global battery roadmaps which focus on expected ultrahigh battery performance, especially for the future of transport. Batteries are used in many applications and are considered to be one technology necessary to reach the climate goals. Currently the market is dominated by lithium-ion batteries, which perform well, but despite new generations coming in the near future, they will soon approach their performance limits. Without major breakthroughs, battery performance and production requirements will not be sufficient to enable the building of a climate-neutral society. Through this “chemistry neutral” approach a generic toolbox transforming the way batteries are developed, designed and manufactured, will be created

Couches minces de phosphates de titane par voie sol-gel

Colloidal solutions of ferroelectrics (KTiOPO$_4$) or ionic conductors (LiTi$_2$(PO$_4$)$_3$) materials have been synthetized. These solutions have been used for thin film synthesis. They are obtained by polycondensation reactions between phosphoric acid esters PO(OH)$_{3-x}$(OR)$_x$ (with $0 < x < 3$ and R = Et, $^{\rm n}$Bu, ...) and titanium alkoxides. The ratio POH/Ti and the amount of hydrolysis and the parameters which control the condensation.Nous avons synthétisé des solutions colloïdales de précurseurs de phosphates tels que des ferroélectriques (KTiOPO$_4$) ou des conducteurs ioniques (LiTi$_2$(PO$_4$)$_3$) adaptées au dépôt en couches minces. Elles sont obtenues par des réactions de polycondensation contrôlées entre les esters de l'acide phosphorique PO(OH)$_{3-x}$(OR)$_x$ (avec $0 < x < 3$ et R = Et, $^{\rm n}$Bu, ... ) et des alcoxydes de titane. Le rapport de POH libres (POH/Ti) et le taux d'hydrolyse (H$_2$O/Ti) sont les paramètres qui contrôlent la condensation

A macroscopic model of the swelling phenomenon of a saturated clay

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Réduction des gels de V

Une réduction douce des gels d oxyde de vanadium peut être réalisée à l'aide de réducteurs organiques ou inorganiques. Elle n entraine pas une destruction du gel tant que la teneur en ions réduits ne dépasse pas 20 %. On observe alors une augmentation de la teneur en eau du xérogel en équilibre avec l'atmosphère ambiante et un accroissement de la distance de base caractéristique de l'organisation monodimensionnelle des particules colloïdales. Ces modifications pourraient être dues à la formation d'ions vanadyle VO++ qui viendraient s'intercaler avec deux couches d'hydratation, entre les fibres de V2O5

Homogeneity-Related Problems in Solution Derived Powders

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