Synthesis and luminescent properties of novel Eu2+-doped silicon oxycarbide glasses

ABSTRACTTwo silicon oxycarbide glasses with different compositions (O/Si ratio 1.2 and 1.8) were prepared by pyrolysis at moderate temperature (900 °C) of polysiloxane precursors. Their structure was investigated using quantitative 29Si solid-state NMR and X-ray photoelectron spectroscopy (XPS). The environment of the silicon atoms in the oxycarbide phase corresponded to a purely random distribution of Si-O and Si-C bonds depending on the O/Si ratio of the glass only and not on the structure of the precursors. At the light of the NMR results, the Si2p XPS spectra of the glasses may be interpreted using the contribution of the five possible SiOxC4-x tetrahedra. The Cls spectra of these glasses indicated the presence of oxycarbide carbon in CSi4 tetrahedra, similar to carbide carbon, and graphitic-like excess carbon.

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Silicon Oxycarbide Glasses from Sol-Gel Precursors

MRS Proceedings ◽

10.1557/proc-271-789 ◽

1992 ◽

Vol 271 ◽

Cited By ~ 44

Author(s):

F. Babonneau ◽

G. D. Soraru ◽

G. D'Andrea ◽

S. Dire ◽

L. Bois

Keyword(s):

Carbon Content ◽

Sol Gel ◽

Mas Nmr ◽

Silicon Oxycarbide ◽

Suitable Choice ◽

Pyrolysis Process ◽

Strong Decrease ◽

Pure Silicon ◽

Silicon Alkoxides ◽

Silicon Oxycarbide Glasses

ABSTRACTSilicon oxycarbide glasses have been prepared from sol-gel precursors containing not only Si-CH3, but also Si-H bonds. Three systems have been chosen containing various Si units but the same C/Si ratio. Their pyrolysis process has been mainly followed by 29Si MAS-NMR and the composition of the final glass extracted. This study shows that a suitable choice of Si-CH3 and Si-H functionnalized silicon alkoxides can lead to a strong decrease in the free carbon content and to an almost pure silicon oxycarbide phase.

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Silicon oxycarbide glasses: Part II. Structure and properties

Journal of Materials Research ◽

10.1557/jmr.1991.2723 ◽

1991 ◽

Vol 6 (12) ◽

pp. 2723-2734 ◽

Cited By ~ 256

Author(s):

Gary M. Renlund ◽

Svante Prochazka ◽

Robert H. Doremus

Keyword(s):

Silicon Carbide ◽

Coefficient Of Thermal Expansion ◽

Random Network ◽

Silicon Oxycarbide ◽

Index Of Refraction ◽

X Ray Diffraction ◽

X Ray ◽

Silicon Oxycarbide Glasses ◽

Oxycarbide Glass ◽

Silicon Oxygen

Silicon oxycarbide glass is formed by the pyrolysis of silicone resins and contains only silicon, oxygen, and carbon. The glass remains amorphous in x-ray diffraction to 1400 °C and shows no features in transmission electron micrographs (TEM) after heating to this temperature. After heating at higher temperature (1500–1650 °C) silicon carbide lines develop in x-ray diffraction, and fine crystalline regions of silicon carbide and graphite are found in TEM and electron diffraction. XPS shows that silicon-oxygen bonds in the glass are similar to those in amorphous and crystalline silicates; some silicons are bonded to both oxygen and carbon. Carbon is bonded to either silicon or carbon; there are no carbon-oxygen bonds in the glass. Infrared spectra are consistent with these conclusions and show silicon-oxygen and silicon-carbon vibrations, but none from carbon-oxygen bonds. 29Si-NMR shows evidence for four different bonding groups around silicon. The silicon oxycarbide structure deduced from these results is a random network of silicon-oxygen tetrahedra, with some silicons bonded to one or two carbons substituted for oxygen; these carbons are in turn tetrahedrally bonded to other silicon atoms. There are very small regions of carbon-carbon bonds only, which are not bonded in the network. This “free” carbon colors the glass black. When the glass is heated above 1400 °C this network composite rearranges in tiny regions to graphite and silicon carbide crystals. The density, coefficient of thermal expansion, hardness, elastic modulus, index of refraction, and viscosity of the silicon oxycarbide glasses are all somewhat higher than these properties in vitreous silica, probably because the silicon-carbide bonds in the network of the oxycarbide lead to a tighter, more closely packed structure. The oxycarbide glass is highly stable to temperatures up to 1600 °C and higher, because oxygen and water diffuse slowly in it.

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