## 2 Results and Discussion  
In order to synthesize polymer-derived SiOC/C ceramics with different compositions, following commercially available preceramic polymer resins were used: Polyramic(r) SPR-212, SPR-684 and SPR-688 (Starfire Systems Inc., Glenville, NY, USA) and BELSIL(r) PMS-MK and SILRES(r) 604 (Wacker Chemie AG, Munich, Germany). Further SiOC/C compositions were obtained from precursors prepared via sol-gel processing upon using different ratios of triethoxysilane TREOS, methyldiethoxysilane MDES, triethoxymethylsilane TEMS or triethoxysilane TEVS (Merck KGaA, Darmstadt, Germany). Table 1 lists the different silicon oxycarbide compositions considered in the present study and the precursors used for their synthesis. A brief summary of the elemental composition of the SiOC/C samples heat treated at T = 1600 \({}^{\circ}\)C is presented in Table 1. It is shown that the total amount of carbon present in the prepared silicon oxycarbide materials can be adjusted over a wide range, i.e., from ca. 7 (sample C-0) up to 55 wt % (sample C-60). Based on the empirical formulae of the prepared materials (Table 2), which can be described as SiO\({}_{2(1\ -\ x)}\)C\({}_{\mathrm{x}}\) + y C (Table 2), it can be stated that the prepared materials show comparable contents of network carbon (i.e., x values range between 0.26 for C-11 and 0.33 for C-36), with the exception of C-17 and C-60, which show an increased network carbon content, i.e., x values of 0.53 and 0.47, respectively. In the series of silicon oxycarbide formulations prepared in the present study, the volume fraction of segregated carbon, which was estimated cf. \[\phi_{\mathrm{C}}=\frac{\left\{\left[y\ -\ \left(1\ -\ \frac{x}{2}\right) \right]\cdot\mathrm{M}_{\mathrm{C}}\right\}/\rho\mathrm{C}}{\left\{\left[y\ -\ \left(1\ -\ \frac{x}{2}\right)\right]\cdot\mathrm{M}_{\mathrm{C}}\right\}/\rho\mathrm{C}+ \left(\left\{\frac{x}{2}\cdot\mathrm{M}_{\mathrm{SiO}_{2}}\right\}/\rho \mathrm{SiO}_{2}\right)+\left(\left\{1\ -\ \frac{x}{2}\ -\ \frac{3x}{4}\cdot\mathrm{M}_{\mathrm{SiC}}\right\}/\rho\mathrm{SiC}\right)} \tag{1}\]  
(with M being the molar mass and \(\rho\) the density of the constituent phases in the studied silicon oxycarbides), may be adjusted between 0 and ca. 58 vol.% (Table 2). Clearly, the synthesis of silicon oxycarbides from suitable precursors allows one to tailor their amount of carbon, especially that of the sp\({}^{2}\)-hybridized, segregated carbon. Consequently, it is expected that the charge carrier transport \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Sample** & **Precursors** & **Ceramic Yield (wt \%)** & **Ref.** \\ \hline \multirow{8}{*}{Sol-Gel Precursors} & \multicolumn{4}{c}{_TREOS:MDES molar ratio_} \\  & C-0 & 10:1 & 87.1 & \\  & C-1 & 2:1 & 88.4 & [41; 42; 43] \\  & C-2 & 1:2 & 86.6 & \\  & \multicolumn{4}{c}{_TREOS:TEMO molar ratio_} \\  & C-4 & 2:1 & 82.2 & \\  & C-6 & 1:1 & 80.7 & this work \\  & C-8 & 1:2 & 78.5 & \\  & \multicolumn{4}{c}{_TREOS:TEVS molar ratio_} \\  & C-13 & 1:1 & 85.0 & \\  & C-15 & 1:2 & 87.6 & this work \\  & C-18 & 1:3 & 88.2 & \\  & C-20 & 1:4 & 85.1 & \\ \hline \multirow{8}{*}{Preceramic Polymers} & C-11 & _PMS MK_ & 81.0 & [44] \\  & C-17 & _SPR 212_ & 85.6 & [12] \\ \cline{1-1}  & C-36 & _Silres 604_ & 84.7 & this work \\ \cline{1-1}  & C-46 & _SPR 688_ & 85.8 & [12] \\ \cline{1-1}  & C-60 & _SPR 684_ & 82.0 & [12] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: SiOC/C-based samples considered in the present study. The number given in the sample name indicates the volume fraction of the segregated carbon phase. behavior in those silicon oxycarbide-based materials may be gradually set from that of an insulator to that of a semimetal, as shown previously [1; 16; 34]. The prepared silicon oxycarbides were investigated by means of Raman spectroscopy.