## 2 Results and Discussion
Figure 1 displays the visible Raman spectra (\(\lambda\) = 514 nm) of the sample C-11, which was heat-treated in argon at different temperatures from 1000 to 1800 \({}^{\circ}\)C. The Raman spectrum of the sample prepared at 1000 \({}^{\circ}\)C exhibited two broad signals at ca. 1330 cm\({}^{-1}\) and ca. 1610 cm\({}^{-1}\) representing the D and G modes, along with a broad, low-intensity signal at 1120 cm\({}^{-1}\), the so-called T band [45]. No significant change is observed in the Raman spectra of the C-11 samples heated at temperatures up to 1400 \({}^{\circ}\)C. However, in the spectrum of the sample annealed at 1400 \({}^{\circ}\)C, the T band, related to residual sp\({}^{3}\) carbon, nearly vanished and the full width at half maximum (FWHM) of the D band significantly narrowed along with an increasing intensity. By comparing the spectra of the samples heat treated at 1400 and 1600 \({}^{\circ}\)C, it could be concluded that the width and intensity of the G band did not significantly change, though a small shoulder around 1620 cm\({}^{-1}\) arose. This signal was assigned to the D' band [45; 46; 47] and indicate the evolution of small nano-graphitic clusters in the silicon oxycarbide sample. This has been substantiated by the appearance and development of two signals (2D and D + G) in the second-order spectrum. Thus, it can be stated that the segregated carbon phase in C-11 increased its ordering as the temperature of heat treatment increased. With increasing crystalline order of the carbon phase, the D \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Element Content (wt \%)**} & \multicolumn{3}{c}{**Empirical Formula**} & \multicolumn{3}{c}{**Volume Fraction (vol.\%)**} \\ \cline{2-7}  & **Si** & **O** & **C** & \multicolumn{2}{c}{**SiO\({}_{\text{2D}-\text{3D}}\)C\({}_{\text{x}}\) + y**} & \multicolumn{2}{c}{**SiO\({}_{\text{2}}\)**} & **SiC** & **C** \\ \hline C-0 & 51.78 & 40.88 & 7.03 & SiO\({}_{\text{1.59}}\)C\({}_{\text{0.31}}\) & 83.2 & 16.8 & - \\ C-1 & 50.97 & 42.14 & 6.89 & SiO\({}_{\text{1.59}}\)C\({}_{\text{2.08}}\) + 0.04C & 84.27 & 14.55 & 1.18 \\ C-8 & 48.38 & 38.69 & 12.93 & SiO\({}_{\text{1.59}}\)C\({}_{\text{0.28}}\) + 0.31C & 77.42 & 14.38 & 8.20 \\ C-11 & 46.65 & 39.40 & 13.95 & SiO\({}_{\text{1.48}}\)C\({}_{\text{0.28}}\) + 0.44C & 76.75 & 12.24 & 11.01 \\ C-17 & 49.13 & 26.44 & 24.43 & SiO\({}_{\text{1.59}}\)C\({}_{\text{0.33}}\) + 0.63C & 54.99 & 27.83 & 17.68 \\ C-36 & 36.53 & 27.90 & 35.57 & SiO\({}_{\text{1.34}}\)C\({}_{\text{0.33}}\) + 19.5C & 51.91 & 11.66 & 36.43 \\ C-46 & 13.72 & 38.23 & 48.05 & SiO\({}_{\text{1.59}}\)C\({}_{\text{0.27}}\) + 2.25C & 26.86 & 26.71 & 46.42 \\ C-60 & 27.96 & 16.93 & 55.11 & SiO\({}_{\text{1.06}}\)C\({}_{\text{0.47}}\) + 4.13C & 30.19 & 12.28 & 57.53 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Elemental composition, empirical formula and estimated phase composition of selected SiOC/ C samples. Figure 1: Raman spectra of sample C-11 heat-treated at different temperatures in the range from 1000 to 1800 \({}^{\circ}\)C (laser wavelength was 514 nm). Green lines represent deconvoluted bands, black circles indicate the experimental curve and the blue line is the fitted curve. band continued to narrow and the D' band became more and more pronounced together with a shift of the G band towards lower wavelengths (Figure 1). Although the advancing graphitization did not lead to an increase of the intensity of the G band, the two signals in the second-order range of the spectrum clearly improved their intensity. In the sample annealed at 1800 \({}^{\circ}\)C, the intensity of the G band was notably increased and the wavelength was downshifted by 30 cm\({}^{-1}\), with the D' band remaining as a small shoulder. In addition, the second-order spectrum markedly differed from those of the samples annealed at lower temperatures, as the band at 2700 cm\({}^{-1}\) had apparently grown in intensity and was displaced by 15 cm\({}^{-1}\) to the lower wavelength. According to [PERSON] et al.