## 2 Results and Discussion
### The Composition of Carbonization Products  
Carbonization was first studied in a tubular furnace at 1000, 1200 and 1400 \({}^{\circ}\)C for 2 h. The effect of reaction time was examined at 1400 \({}^{\circ}\)C--holding time was increased up to 8 h. Orthorhombic and tetragonal ZrO\({}_{2}\) were detected as primary decomposition products at 1000 \({}^{\circ}\)C. The orthorhombic/tetragonal ratio strongly depended on Zr loading and was 1.36, 0.77 and 0 for the samples with X=Cl, N and S, respectively. Furthermore, the crystallite sizes of ZrO\({}_{2}\) particles ranged between 5 and 10 nm for these samples (Table 2). As carbonization temperature was increased to 1200 \({}^{\circ}\)C, a cubic ZrC\({}_{0.58}\) (\(a\) = 4.6690 A, Fm3m) appeared as the main reaction product (75, 65 and 50 mass% ZrC and 15, 25 and 10 mass% ZrO\({}_{2}\) content for X=Cl, N and S, with a crystallite size of \(\sim\)10 nm in every case (Table 2)). The exact composition of ZrC was calculated from the lattice constants determined by XRD (Figure 5 and Supplementary Materials, Figure S11), with the [PERSON] equation [35], which was valid for ZrC\({}_{\rm x}\) samples with 0.5 \(<\)\(x\)\(<\) 1.0. [PERSON]'s equation [36] valid for samples 0.65 \(<\)\(x\)\(<\) 01.0 did not give results in this range, which shows that \(x\) is out of the validity range of the equation. Residual amorphous carbon content would be \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **ZrC**, & **ZrO\({}_{2}\)** & **Carbon** & **BT Surface Area** \\
**Composite** & **(wt\%)** & **(wt\%)** & **(wt\%)** & **(m\({}^{2}\)/g)** \\  & **(Size in nm)** & **(Size in nm)** & **(Size in nm)** & **(wt\%)** & **(m\({}^{2}\)/g)** \\ \hline L-Zr-Cl-1000-2 & - & 65 (5) & 35 & 140 \\ L-Zr-Cl-1200-2 & 75 (10) & 15 (11) tetra & 10 & 311 \\ L-Zr-Cl-1400-2 & 80 (10) & 10 (12) tetra & 10 & 310 \\ L-Zr-Cl-1400-8 & 85 (14) & 5 (26) tetra/mono = 1.92 & 10 & 245 \\ L-Zr-N-1000-2 & - & 80(5) & 20 & 278 \\ L-Zr-N-1200-2 & 65 (10) & 25 (7) tetra & 10 & 447 \\ L-Zr-N-1400-2 & 95 (17) & - & 5 & 430 \\ L-Zr-N-1400-8 & 95 (18) & - & 5 & 438 \\ L-Zr-S-1000-2 & - & 10 (8) & 90 & 33 \\ L-Zr-S-1200-2 & 50 (8) & 10 (8) & 40 & 41 \\ L-Zr-S-1400-2 & 30(13) & 15 (8) tetra & 55 & 54 \\ L-Zr-S-1400-8 & 50 (56) & 5 (31) & 55 & 35 \\  & & mono/cubic = 1.05 & 55 & 35 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Composition and properties of (ZrC\({}_{0.58}\), ZrO\({}_{2}\))@C composites prepared from L-Zr-Cl, L-Zr-N and L-Zr-S resins in a tubular furnace. enough to form stoichiometric ZrC by incorporating carbon into the ZrC\({}_{0.58}\) structure at high-temperature heat treatment [37; 38]. Thus, two sets of heat-treatment tests were carried out at 1400 \({}^{\circ}\)C with treatment times of 2 h and 8 h, and an RF plasma treatment was also performed in an H\({}_{2}\) and He atmosphere on nano-ZrO\({}_{2}\)@C samples with Zr/C atomic ratios of ~5.8, ~6.8 and 6.64. The heating time of 2 h at 1400 \({}^{\circ}\)C resulted in ZrC\({}_{0.58}\)@C (X=N) and (ZrC\({}_{0.58}\),ZrO\({}_{2}\))@C composites with a ZrC\({}_{0.58}\)/ZrO molar ratio of 8 and 2 (Table 2). ZrO\({}_{2}\) was only detected as its tetragonal modification in these samples. Increasing the heating time to 8 h resulted in an increasing ZrC\({}_{0.58}\) content and a partial transformation of ZrO\({}_{2}\) into its monoclinic form (the tetragonal/monoclinic ratio was 2 and 5 for X=Cl and S, respectively). The crystallite sizes of ZrC\({}_{0.58}\) ranged between 10 and 20 nm. Neither graphite nor Zr\({}_{3}\)C\({}_{2}\) was found in these samples. Even under prolonged heating, additional carbon atoms were not incorporated into the ZrC\({}_{0.58}\) structure. The reactivity of ZrO\({}_{2}\) and carbon species in composites prepared from various Zr-loaded resins with various zirconium content was different in the carbonization reactions, despite the lack of foreign anions in the L-Zr-X samples. Therefore, we studied the behavior of all three L-Zr-X-1000-2  
Figure 5: XRD pattern of L-Zr-X-1400-8 and L-Zr-X-1000-2-P-He (X=Cl, N and S) samples.