Inorganic–organic nanocomposites of CdSe nanocrystals surface-modified with oligo- and poly(fluorene) moieties

We report a facile grafting-from strategy towards the synthesis of inorganic–organic composites of semiconductor nanocrystals and wide-bandgap polymers. Amino-functional fluorenes have been used as co-ligands for CdSe nanocrystals, thus enabling us to design their surface directly during the synthesis. Highly monodisperse, strongly emitting CdSe nanocrystals have been obtained. Subsequently, a straightforward Yamamoto C–C coupling protocol was used to carry out surface polymerisation, hence modifying CdSe nanocrystals with oligo- and poly(fluorene) moieties. Both amino-fluorene capped CdSe nanocrystals and the resulting nanocrystal–polymer composites were characterized in detail by optical and FT-IR spectroscopy, TEM, AFM, and gel permeation chromatography, showing their potential as novel functional inorganic–organic hybrid materials

Quantification of titanium dioxide (TiO2) anatase and rutile polymorphs in binary mixtures by Raman spectroscopy: an interlaboratory comparison

This article presents an interlaboratory comparison (ILC) on Raman spectroscopy as a technique for relative quantification of the two most common polymorphs of titanium dioxide (TiO2)-anatase and rutile-in binary mixtures. Some standard methods are currently employed internationally for the determination of TiO2 content in samples (ISO 591-1, ASTM D3720-90), but require extensive sample preparation, do not distinguish between the two polymorphs or are accurate only for small fractions of either polymorph. Raman spectroscopy is a well-suited characterization technique for measuring and differentiating TiO2 in a fast, non-invasive way, while requiring no particular reagent or sample preparation. Eleven international participants conducted the study under the framework of Versailles Project on Advanced Materials and Standards. The collected data was analyzed by means of partial least squares regression after spectral preprocessing. The resulting models all show discrepancies of lower than 2% from the nominal values in the quantitative analysis over the concentration range of 5%-95% mixture fractions, with many datasets showing substantial improvement margins on this figure. The results of this ILC provide validation of Raman spectroscopy as a reliable method for quantification of TiO2 phases

Realstruktur des FeNbO4 und elektronische Materialeigenschaften

Im Mittelpunkt dieser Arbeit steht die strukturelle Charakterisierung des FeNbO4 in seinen Polymorphen II und III. Die Sichtung der einschlägigen Literatur und die Auswertung eigener Vorarbeiten lassen die Schlüsse zu, daß der kristalline Aufbau des FeNbO4 signifikante Störungen aufweist, und daß sich diese Störungen offenbar auf die Matreialeigenschaften auswirken. Die Aufklärung der Realstruktur des Eisenniobates ist somit wichtige Voraussetzung für das Verständnis seiner Eigenschaften. Zentrale Bedeutung für das Auftreten einer Realstrukturierung im FeNbO4 hat die Existenz eines Ordnungs-Unordnungs-Phasenübergangs von FeNbO4-II zu FeNbO4-III im Temperaturbereich zwischen 1100°C und 1050°C. Dieses Temperaturintervall liegt im unteren Bereich der möglichen Sintertemperaturen des keramischen Materials und wird in fast allen veröffentlichten Synthesevorschriften mehrfach durchschritten. Um den Einfluß des Phasenübergangs auf die Realstruktur systematisch zu untersuchen wurde eine geeignete Variation der Syntheseparameter durchgeführt. Die Charakterisierung der Proben erfolgte mittels röntgenographischer und elektronenmikroskopischer Methoden. Es wurde eine Realstruktur beobachtet, die sich mit Hilfe von drei Parametern (Domänengröße, Ordnungsgrad, Zustand des Kristallgitters) eindeutig beschreiben läßt. Eine Quantifizierung der erwähnten Parameter wurde durch die Aufstellung eines geeigneten Modells für die Rietveld-Analyse erreicht. Des weiteren wurden Messungen bezüglich der elektrischen und magnetischen Eigenschaften durchgeführt. Ein systematischer Einfluß der Realstruktur konnte in beiden Fällen eindeutig nachgewiesen werden. Daraus resultiert eine potentielle Anwendbarkeit des Materials als Halbleitergassensor. Eine weitergehende Modellierung oder theoretische Beschreibung der genannten Eigenschaften ist aufgrund der komplexen Realstruktur sehr schwierig und steht noch aus

Influence of Boron on the Microstructure of Polymer Derived SiCO Ceramics

Polymer-derived silicon oxycarbide or carbonitride based ceramics are presently discussed for application as protective coatings,[1]fibers,[2]ceramic matrix composites[3]and high temperature resistant material. In contrast to sintering of fine ceramic powders the aforementioned ceramics investigatedhere are produced by pyrolysis of polymer precursors. Dueto the tailorability of the molecular structures thermal decomposition of preceramic polymers led to increasing research efforts in the field of the search for novel ceramic materials. Polymers can be formed by techniques like pressure casting or injection moulding. Consequently, pyrolysis of preceramic polymers is considered to be an interesting alternative pro- cess for the fabrication of complex shaped ceramic parts

Influence of boron on the microstructure of polymer-derived SiCO ceramics

Polymer-derived silicon oxycarbide or carbonitride based ceramics are presently discussed for application as protective coatings,[1]fibers,[2]ceramic matrix composites[3]and high temperature resistant material. In contrast to sintering of fine ceramic powders the aforementioned ceramics investigatedhere are produced by pyrolysis of polymer precursors. Dueto the tailorability of the molecular structures thermal decomposition of preceramic polymers led to increasing research efforts in the field of the search for novel ceramic materials. Polymers can be formed by techniques like pressure casting or injection moulding. Consequently, pyrolysis of preceramic polymers is considered to be an interesting alternative pro- cess for the fabrication of complex shaped ceramic parts

Thermal degradation of microporous Sm2O3–MgO nanocomposites at isothermal conditions and surface chemical properties

The evolution of microstructural, morphological and surface chemical properties of Sm2O3–MgO nanocomposites are determined during and after isothermal heat treatments in the range of 500–1000 °C. The samples are investigated using (high temperature) X-ray diffraction, energy-filtered transmission electron microscopy including electron energy loss spectroscopy, nitrogen adsorption, and temperature programmed desorption of CO2. With small amounts of MgO the initial micropore fractions are low and mainly coarsening of Sm2O3 is observed. Large amounts of MgO result in high initial micropore fractions giving rise to enhanced densification. The different thermal degradation behaviors are explained by means of the respective characteristic diffusion distances which are determined by the volume phase fractions. The surface chemical properties of Sm2O3 and MgO remain qualitatively unchanged, however, the specific CO2 chemisorption capacities are increased through the nanocomposite formation

A reproducible number-based sizing method for pigment-grade titanium dioxide

A strong demand for reliable characterization methods of particulate materials is triggered by the prospect of forthcoming national and international regulations concerning the classification of nanomaterials. Scientific efforts towards standardized number-based sizing methods have so far been concentrated on model systems, such as spherical gold or silica nanoparticles. However, for industrial particulate materials, which are typically targets of regulatory efforts, characterisation is in most cases complicated by irregular particle shapes, broad size distributions and a strong tendency to agglomeration. Reliable sizing methods that overcome these obstacles, and are practical for industrial use, are still lacking. By using the example of titanium dioxide, this paper shows that both necessities are well met by the sophisticated counting algorithm presented here, which is based on the imaging of polished sections of embedded particles and subsequent automated image analysis. The data presented demonstrate that the typical difficulties of sizing processes are overcome by the proposed method of sample preparation and image analysis. In other words, a robust, reproducible and statistically reliable method is presented, which leads to a number-based size distribution of pigment-grade titanium dioxide, for example, and therefore allows reliable classification of this material according to forthcoming regulations

High pressure synthesis of a gallium oxonitride with a spinel-type structure

The new compound Ga2.81O3.57N0.43 was crystallized under high-pressure / high-temperature conditions in a spinel-type structure from a prestructured gallium oxonitride ceramic, which was obtained from the single-source molecular precursor [Ga(OtBu)2NMe2]2 by thermal treatment in an ammonia atmosphere. The optimized precursor-derived gallium oxonitride ceramic remains nanocrystalline up to 600 °C and can be transformed at 7 GPa and 1100 °C into the crystalline phase Ga2.81O3.57N0.43. The structure, homogeneity, and nitrogen to oxygen ratio were determined using TEM coupled with an electron energy loss spectrometer (EELS) and an energy dispersive X-ray (EDX) spectrometer. For phase analysis and structure confirmation, X-ray powder diffraction data were measured