## 3 Results and Discussion
### Hydration Behavior  
Thermogravimetric analysis was performed for the preliminarily hydrated La\({}_{2}\)ScZnO\({}_{5.5}\) and all doped samples. The TG curves for all investigated samples are shown in Figure 4. All TG curves are characterized by mass loss. The mass spectrometry analysis confirmed that the mass changes can be attributed to water removal and no other volatile components (such as CO\({}_{2}\) or O\({}_{2}\)) were detected. Figure 4 also shows the MS curve for hydrated sample La\({}_{1.9}\)Ca\({}_{0.1}\)ScZnO\({}_{5.45}\), as a typical example. The peaks of water removal on the MS curve corresponded to the stages of mass loss on the TG curve. According to the TG data for doped samples, the main mass loss occurred in the temperature range of 300-400 \({}^{\circ}\)C and the second stage of mass loss took place at 500-550 \({}^{\circ}\)C. The temperature ranges of these dehydration steps were the same for all doped samples. At the same time, the undoped sample La\({}_{2}\)ScZnO\({}_{5.5}\) exhibited one effect of mass loss at the temperature of approximately 500-550 \({}^{\circ}\)C. For all samples, water was completely removed at T \(>\) 600 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Formula** & \(\mathbf{a}\), Å & \(\mathbf{b}\), Å & \(\mathbf{c}\), Å & \(\mathbf{V}\) *, Å3 & \(\mathbf{V}\) ** ** **\(\mathbf{{}_{\text{free}}}\) Å3** \\ \hline La\({}_{2}\)ScZnO\({}_{5.5}\) & 5.796 (5) & 8.101 (9) & 5.683 (4) & 66.73 & 26.15 \\ \hline La\({}_{2}\)Sc\({}_{0.9}\)Mg\({}_{0.1}\)ZnO\({}_{5.45}\) & 5.792 (7) & 8.095 (7) & 5.678 (9) & 66.58 & 26.27 \\ \hline La\({}_{2}\)Sc\({}_{0.9}\)Ca\({}_{0.1}\)ZnO\({}_{5.45}\) & 5.813 (3) & 8.116 (2) & 5.685 (7) & 67.06 & 26.63 \\ \hline La\({}_{1.9}\)Ca\({}_{0.1}\)ScZnO\({}_{5.45}\) & 5.794 (7) & 8.099 (8) & 5.681 (7) & 66.67 & 26.38 \\ \hline La\({}_{2}\)InZnO\({}_{5.5}\)[47] & 5.941 (2) & 8.217 (1) & 5.723 (7) & 69.86 & 29.08 \\ \hline La\({}_{2}\)AlZnO\({}_{5.5}\)[46] & 3.7932 (1) & – & – & 54.58 & 14.55 \\ \hline \end{tabular}
*Unit cell volume divided by Z. ** Lattice free volume is defined as the volume of the ions in the formula unit (\(Z=4\)) subtracted from the unit cell volume divided by Z, where Z is a number of formula units.  
\end{table} 
Table 1: The lattice parameters for La\({}_{2}\)ScZnO\({}_{5.5}\) and doped phases in comparison with the literature data for La\({}_{2}\)InZnO\({}_{5.5}\)[47] and La\({}_{2}\)AlZnO\({}_{5.5}\)[46]. These results show that the states of the OH\({}^{-}\) groups in hydrated doped and undoped samples are different; therefore, different types of protonic species with different thermal stability are present in doped phases. The introduction of the dopants leads to the appearance of a part of OH\({}^{-}\) groups with a lower thermal stability. A possible cause may be different types of oxygen vacancies. It is well known that protons can dissolve in oxygen-deficient phases through contact with water vapor. The water insertion into the structure of oxides can be represented as a process of dissociative dissolution of water with the formation of proton defects (OH\({}^{-}\) groups) and the reaction can be written by the Kroger-Vink notation as follows [52]:  
\[H_{2}O+O_{o}^{\times}+V_{o}^{\times}\rightarrow(OH)^{\prime}_{o}+(OH)^{\bullet }_{O}, \tag{4}\]  
where \(V_{o}^{\times}\) is the structural oxygen vacancy, \(O_{o}^{\times}\) is the oxygen on regular sites, \((OH)^{\bullet}_{O}\) is the hydroxide group (a proton incorporated into the electron cloud of a regular oxygen atom) and \((OH)^{\prime}_{o}\) is the hydroxide group in the site of a structural oxygen vacancy. This equation is used for structural oxygen vacancies, i.e., in the case of oxygen deficiency is created by placing two cations with different charges into the B-sublattice. That is, for the undoped phase La\({}_{2}\)ScZnO\({}_{5.5}\) [\(V_{o}^{\times}\)]\({}_{0.5}\) with structural oxygen vacancies, the hydration process can be recorded as well.