Search results for "CERAMICS"

Oxidative C-N fusion of pyridinyl-substituted porphyrins.

2018

International audience; The mild (electro) chemical oxidation of pyridin-2-ylthio-meso substituted Ni(II) porphyrins affords C-N fused cationic and dicationic pyridinium-based derivatives. These porphyrins are fully characterized and the molecular structure of one of them was confirmed by X-ray crystallography. A mechanism for the intramolecular oxidative C-N coupling is proposed based on theoretical calculations and cyclic voltammetry analyses.

Dielectric properties of barium strontium titanate / non ferroelectric oxide ceramic composites

2001

International audience; Barium strontium titanate ceramics present high dielectric permittivity and tunability. In order to reduce their permettivity and loss tangent while keeping tunability, various composites of barium strontium titanate oxide...

EPR Study of Manganese-Doped PLZT-8/65/35 Ceramics

1992

Synthesis and reactivity of cristobalite obtained from the SiO2-V2O5 system

1990

On etudie par diffraction RX l'evolution des phases cristallines lors de la cuisson a 650-1250 o C de compositions du systeme ZrO 2 −V 2 O 5 −SiO 2 et la reactivite de la cristobalite preparee avec la phase ZrO 2 monoclinique

X-ray powder diffraction phase analysis and thermomechanical properties of silica and alumina porcelains

2004

Chemical and mineralogical characterization, using the Rietveld method, of some silica and alumina rich porcelains and its relationship with thermomechanical properties have been studied in this work. X-ray powder diffraction analysis allows to differ clearly between silica and alumina porcelains. X-ray study shows that both porcelains have a content of vitreous phase. This vitreous phase is higher in the silica than in the alumina porcelain. Dilatometric studies combined with powder diffraction methods shows a strong relationship between silica content and a lower expansion coefficients and between alumina content and a higher crash resistance. Lower contents in vitreous phase in porcelain…

The solubility of Co in TiO2 anatase and rutile and its effect on the magnetic properties

2009

Co-doped anatase and rutile bulk-samples prepared by the sol-gel technique are found to be paramagnetic at room-temperature. Only further annealing in Ar/H{sub 2} gas results in a ferromagnetic behavior. X-ray diffraction and electron-microscope studies reveal for low doping levels =4%. The observed Co oxides are reduced by Ar/H{sub 2} to Co metal. The room-temperature ferromagnetism can therefore be traced back to a segregation of metallic Co. - Graphical abstract: Co-doped anatase and rutile bulk-samples prepared by the sol-gel technique are paramagnetic at room-temperature. Further annealing in Ar/H{sub 2} gas results in a ferromagnetic behavior. X-ray diffraction and electron-microscope…

A photoresponsive graphene oxide-C60 conjugate.

2014

An all-carbon donor-acceptor hybrid combining graphene oxide (GO) and C60 has been prepared. Laser flash photolysis measurements revealed the occurrence of photoinduced electron transfer from the GO electron donor to the C60 electron acceptor in the conjugate

Organocatalytic enantioselective synthesis of 2,5,5-trisubstituted piperidines bearing a quaternary stereocenter. Vinyl sulfonamide as a new amine pr…

2020

An organocatalytic desymmetrizing intramolecular aza-Michael reaction with vinyl sulfonamides as nucleophilic nitrogen source has been devised for the synthesis of a new family of 2,5,5-trisubstituted piperidines bearing a quaternary sterocenter. The process takes place with excellent levels of enantioselectivity and moderate to good diastereoselectivity. The vinyl sulfonamide moiety can be removed by means of an ozonolysis reaction.

Stoichiometry-related Auger lineshapes in titanium oxides: Influence of valence-band profile and of Coster-Kronig processes

2004

International audience; The ability to determine the nature and the occurrence of defects is a central need of ceramic surface chemistry. In titanium oxides, the Ti-LMV Auger decays line shape is very sensitive to the titanium degree of oxidation, and has long been empirically used as a qualitative probe of the stoichiometry. In the present work, resonant Auger and resonant valence-band measurements at the Ti-L2,3 edges in TiO2, TiO2–x and metallic titanium provide a clear evidence that the evolutions of the Ti-LMV Auger line shape are due to drastic changes in the valence-band profile and in the probability of L2L3V Coster-Kronig decay processes when a fraction of titanium ions is reduced.…

Boron–nitrogen substituted dihydroindeno[1,2-b]fluorene derivatives as acceptors in organic solar cells

2019

The electrophilic borylation of 2,5-diarylpyrazines results in the formation of boron–nitrogen doped dihydroindeno[1,2-b]fluorene which can be synthesized using standard Schlenk techniques and worked up and handled readily under atmospheric conditions. Through transmetallation via diarylzinc reagents a series of derivatives were synthesized which show broad visible to near-IR light absorption profiles that highlight the versatility of this BN substituted core for use in optoelectronic devices. The synthesis is efficient, scalable and allows for tuning through changes in substituents on the planar heterocyclic core and at boron. Exploratory evaluation in organic solar cell devices as non-ful…