High-Temperature Raman Spectroscopy of Nano-Crystalline Carbon in Silicon Oxycarbide

Abstract

The microstructure of segregated carbon in silicon oxycarbide (SiOC), hot-pressed at T = 1600 °C and p = 50 MPa, has been investigated by VIS Raman spectroscopy (λ = 514 nm) within the temperature range 25–1000 °C in air. The occurrence of the G, D’ and D bands at 1590, 1620 and 1350 cm−1, together with a lateral crystal size La < 10 nm and an average distance between lattice defects LD ≈ 8 nm, provides evidence that carbon exists as nano-crystalline phase in SiOC containing 11 and 17 vol % carbon. Both samples show a linear red shift of the G band up to the highest temperature applied, which is in agreement with the description of the anharmonic contribution to the lattice potential by the modified Tersoff potential. The temperature coefficient χG = −0.024 ± 0.001 cm−1/°C is close to that of disordered carbon, e.g., carbon nanowalls or commercial activated graphite. The line width of the G band is independent of temperature with FWHM-values of 35 cm−1 (C-11) and 45 cm−1 (C-17), suggesting that scattering with defects and impurities outweighs the phonon-phonon and phonon-electron interactions. Analysis of the Raman line intensities indicates vacancies as dominating defects.

POSS-Containing Polymethacrylates on Cellulose-Based Substrates: Immobilization and Ceramic Formation

“…Complementary Raman spectroscopy investigations of the thermally treated materials ( Figure S14) revealed the presence of highly disordered sp 2 -hybridized carbon, which increased slightly its crystallinity upon thermal treatment at 1600 °C. These findings are in very good agreement with the IR signals described above and with findings from other studies [65,66]. In case of the thermally treated cellulose substrate under nitrogen atmosphere, IR spectra for all investigated cellulose substrates revealed same transmission band signals between 1770 and 4000 cm −1 .…”

“…Additional XRD measurements of the biotemplated cellulose substrate revealed Bragg reflections, which can be assigned to β-SiC containing high densities of stacking faults ( Figure S13) [64], proving the feasibility of the herein investigated functionalization approach for the preparation of porous silicon-containing ceramic materials with hierarchically ordered domains. Complementary Raman spectroscopy investigations of the thermally treated materials ( Figure S14) revealed the presence of highly disordered sp 2 -hybridized carbon, which increased slightly its crystallinity upon thermal treatment at 1600 • C. These findings are in very good agreement with the IR signals described above and with findings from other studies [65,66]. Summarizing the morphological characterizations thermally treated PMAPOSS-modified cellulose substrates revealed almost complete decomposition of the fibre structure, while for the same substrates treated under nitrogen, the fibre morphology was preserved additionally featuring siliconcontaining spherical domains at the cellulose-templated fibre structure.…”

Enhanced electromagnetic wave absorbing properties of Si‐O‐C ceramics with in‐situ formed 1D nanostructures

“…12,18 The L a crystallite size (nm) calculated by integrated intensity ratio I D /I G is given by 19 λ L is the laser line wavelength in nanometer units (514.5 nm in this work). I D /I G is usually used to evaluate the disordered degree of free carbon, where I D and I G is the intensity of disorder-induced (D) and graphite-like (G) bands, respectively.…”

“…I D /I G is usually used to evaluate the disordered degree of free carbon, where I D and I G is the intensity of disorder-induced (D) and graphite-like (G) bands, respectively. 12,18 The L a crystallite size (nm) calculated by integrated intensity ratio I D /I G is given by 19 λ L is the laser line wavelength in nanometer units (514.5 nm in this work). Figure 5 indicates the ordered degree of the formed free carbon in the Si-O-C matrix.…”

Effect of composition and high-temperature annealing on the local deformation behavior of silicon oxycarbides

“…The abundance of each tetrahedral unit depends on the chemical composition and thus, the polymeric precursor used for the glass preparation. In addition to the covalently bonded C linked to Si (network carbon), typical SiOC glasses also contain a sp 2 -hybridized segregated carbon phase, which is homogeneously dispersed in the SiOC glass matrix [7,8]. At temperatures above 1250 °C, phase separation of the amorphous SiOC glass starts, as evident from the vanishing signals for SiO3C, SiO2C2 and SiOC3 tetrahedral units in the 29 Si MAS NMR spectra [7,9].…”