## 3 Results and Discussion
Since the set of peaks in the powder diffractogram of the tetragonal zirconium oxide phase closely resembled those of the cubic ZrO\({}_{2}\)-c phase, Raman spectroscopy (Figure 2b) was employed to clarify the phase composition of the synthesized ceramics. In the case of pure zirconium oxide sintered at 1500 \({}^{\circ}\)C, fourteen active modes were observed: seven A\({}_{\mathrm{g}}\) (178, 190, 306, 346, 475, 558, and 636 cm\({}^{-1}\)), six B\({}_{\mathrm{g}}\) (221, 333, 381, 503, 536, and 615 cm\({}^{-1}\)), characteristic of the monoclinic phase [32], and a peak at 581 cm\({}^{-1}\), which disappeared at a \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{\(\mathbf{R_{exp}}\)} & \multirow{2}{*}{\(\mathbf{R_{wp}}\)} & \multirow{2}{*}{**GOF**} & \multirow{2}{*}{\(\chi^{2}\)} & \multicolumn{4}{c}{**Phase Composition, \%**} \\ \cline{5-8}  & & & & & & **ZrO\({}_{2}\)-m** & **ZrO\({}_{2}\)-c** & **CaZrO\({}_{3}\)** \\ \hline ZrO\({}_{2}\) & 4.02 & 6.07 & 1.51 & 2.28 & 100 & 0 & 0 \\
0.05 & 3.45 & 4.55 & 1.32 & 1.74 & 63.45 & 36.55 & 0 \\
0.10 & 3.77 & 6.36 & 1.69 & 2.85 & 8.75 & 91.25 & 0 \\
0.15 & 3.63 & 5.85 & 1.61 & 2.60 & 2.82 & 97.18 & 0 \\
0.20 & 4.32 & 6.78 & 1.57 & 2.46 & 0 & 88.60 & 11.40 \\
0.25 & 3.69 & 5.51 & 1.49 & 2.23 & 0 & 64.58 & 34.42 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistical parameters of Rietveld refinement and phase composition obtained from the analysis of diffractograms. Figure 2: W-H dependence for undoped ZrO\({}_{2}\) (**a**) and Raman spectra of synthesized ceramics (**b**). Ca concentration of 0.05. The spectra of the samples with Ca concentrations of 0.10 and 0.15 showed only three very broad peaks at 156, 277, and 608 cm\({}^{-1}\), associated with the cubic phase of the fluorite structure (O\({}^{5}\), \(\mathrm{r_{m-3m}}\)) [16]. At a Ca concentration of 0.20, the broad peaks of the cubic phase were still pronounced, but new sharp peaks also began to appear. Finally, for a Ca concentration of 0.25, Raman modes were observed at 146, 190, 212, 230, 262, 286, 309, 358, 438, 470, and 546 cm\({}^{-1}\), indicating the formation of orthorhombic perovskite-phase CaZrO\({}_{3}\)[33]. Notably, the peak at 610 cm\({}^{-1}\) indicated the cubic phase of zirconium oxide. Thus, the results of the powder diffractogram analysis were enhanced using Raman spectroscopy. Figure 3 shows microphotographs of the cross-sections of the obtained ceramics. The microstructure of the undoped sample (Figure 3a) was characterized by the presence of well-defined grains with a large number of faces, a pronounced intergrain boundary, and the presence of intergrain pores. The mentioned grain shape is largely characteristic of crystallites with a monoclinic crystal lattice. When the dopant was introduced at a concentration of C\({}_{w}\) = 0.05 (Figure 3b), significant changes in the microstructure occurred. In addition to grains with sizes of 2-3 \(\upmu\)m, smaller grains and larger grains with sizes of 6-8 \(\upmu\)m were formed. Upon further increasing the proportion of CaCO\({}_{3}\) in the charge, the microstructure of the synthesized ceramics (Figure 3c-f) exhibited grains with relatively complex shapes. This complexity arose from the sintering process, resulting in the fusion of individual grains. Additionally, there was a reduced number of intergranular boundaries, and the presence of intergrain pores was observed. Figure 3: _Cont._  
For a more detailed analysis of the microstructure of the synthesized samples, the grain size distribution in the ceramics was evaluated using ImageJ software 1.54f [34]. For the set of statistics, the sizes of 100 grains were determined from the SEM micrographs.