## 3 Results and Discussion
Thus, it can be stated that the increased value of the lattice parameters in the undoped ceramics is due to tensile stresses. These stresses arise during cooling, when a transition from the tetragonal phase to the monoclinic phase occurs. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sample** & \multicolumn{4}{c}{**Monoclinic Phase**} & \multicolumn{4}{c}{**Cubic Phase**} \\ \hline  & **a, Å** & **b, Å** & **c, Å** & **b, \({}^{\circ}\)** & **V, Å3** & **XRD** & **c, Å** & **V, Å3** & **XRD** \\  & **a, Å** & **b, Å** & **c, Å** & **b, \({}^{\circ}\)** & **V, Å3** & **Density, g/cm3** & **a, Å** & **V, Å3** & **Density, g/cm3** \\ \hline ZrO\({}_{2}\) & 5.1509 & 5.2060 & 5.3215 & 99.22 & 140.855 & 5.810 & - & - & - \\ \hline
0.05 & 5.1537 & 5.2044 & 5.3191 & 99.22 & 140.825 & 5.811 & 5.1272 & 134.785 & 6.072 \\ \hline
0.10 & 5.1468 & 5.1973 & 5.3199 & 99.21 & 140.469 & 5.826 & 5.1292 & 134.943 & 6.014 \\ \hline
0.15 & 5.1367 & 5.1993 & 5.3264 & 99.21 & 140.420 & 5.828 & 5.1381 & 135.646 & 6.033 \\ \hline \end{tabular}
\end{table} 
Table 1: Results of quantitative analysis of diffractograms via the Rietveld method for ceramics with monoclinic and cubic phases. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Sample** & \multicolumn{4}{c}{**Cubic Phase**} & \multicolumn{4}{c}{**Perovskite Phase**} \\ \hline  & **a, Å** & **V, Å3** & **XRD** & **Density, g/cm3** & **a, Å** & **b, Å** & **c, Å** & **V, Å3** & **XRD** \\  & **a, Å** & **V, Å3** & **Density, g/cm3** & **a, Å** & **b, Å** & **c, Å** & **V, Å3** & **Density, g/cm3** \\ \hline
0.20 & 5.13707 & 135.565 & 6.037 & 5.6001 & 5.7526 & 8.0157 & 258.2269 & 4.612 \\ \hline
0.25 & 5.1411 & 135.884 & 6.022 & 5.5940 & 5.7561 & 8.0174 & 258.1573 & 4.613 \\ \hline \end{tabular}
\end{table} 
Table 2: Results of quantitative analysis of diffractograms via the Rietveld method for ceramics with perovskite and cubic phases. The average crystalline size was calculated using the Debye-Scherer equation for all samples. The main characteristic peaks of each phase were also fitted using Profex 5.0.2 software. The results of this calculation are presented in Figure 1. The lowest crystalline size for an undoped sample can be explained by tensile stresses in the crystal structure. It is observed that with increasing Ca content in sintered ceramics, the average crystallites become larger. The possible reason for this fact is that in stabilized cubic zirconia, during the cooling \(\mathrm{t}\rightarrow\mathrm{m}\) transformation, significant distortion of the crystal lattice does not occur. This leads to the relaxation of tensile stresses and increases the crystallite size. Table 3 lists the statistical parameters of the Rietveld refinement and phase composition of the obtained ceramics. The parameters R-factor (\(\mathrm{R_{exp}}\), \(\mathrm{R_{wp}}\)), goodness of fit (GOF), and standard deviation \(\chi^{2}\) exhibit relatively low values, indicating the fitting results' reliability. These low values imply a small difference between the experimental and calculated data, thus affirming the accuracy of the fitting process. Based on the evaluation of the phase composition and lattice parameters of the resulting ceramics, it can be concluded that an increase in CaCO\({}_{3}\) concentration leads to the following changes in the phase composition: ZrO\({}_{2}\)-m transitions to ZrO\({}_{2}\)-m + ZrO\({}_{2}\)-c with the substitution of Zr\({}^{4+}\) by Ca\({}^{2+}\) ions in the range of C\({}_{\mathrm{w}}\) = 0.05-0.15; ZrO\({}_{2}\)-c coexists with CaZrO\({}_{3}\), reaching the substitution limit with the separation of the second phase. Moreover, by varying the dopant concentration from 0 to 0.10, it is possible to obtain partially stabilized zirconium oxide ceramics. At a concentration of 0.15, fully stabilized ceramics are formed. In the concentration range of 0.20 to 0.25, partially stabilized zirconia ceramics with a fraction of CaZrO\({}_{3}\) are obtained.