## 3 Results and Discussion
It is obvious (Table 3) that below 800 \({}^{\circ}\)C the activation energies for conduction in the Ln\({}_{2}\)(Hf\({}_{1.9}\)Ln\({}_{0.1}\))O\({}_{6.95}\) (Ln = La, Nd) \"stuffed\" hafnate pyrochlores in wet air are lower than those in dry air. This is usual proton conductor behaviour. Ln\({}_{2}\)(Hf\({}_{1.9}\)Ln\({}_{0.1}\))O\({}_{6.95}\) (Ln = Sm, Eu) \"stuffed\" pyrochlores have the same activation energy (Table 3) for conductivity, which is independent of humidity. Figure 3: Arrhenius plots of conductivity for different \(Ln_{2}\)(Hf\({}_{1.9}\)Ln\({}_{0.1}\))O\({}_{6.95}\) “stuffed” hafnate pyrochlores ((1) \(Ln\) = La; (2) Nd [22]; (3) Sm [16]; (4) Eu) [16] in dry and wet air. \begin{table}
\begin{tabular}{c c c c c} \hline \multicolumn{2}{c}{**Composition**} & \multirow{2}{*}{**Atmosphere**} & **Temperature** & **E\({}_{\text{a}}\) (\(\pm\)0.01), eV** & **References** \\ \cline{3-5} \(Ln_{2}\)(Hf\({}_{1.9}\)Ln\({}_{0.1}\))O\({}_{6.95}\) & & **Range**, \({}^{\circ}\)C & **E\({}_{\text{a}}\) (\(\pm\)0.01), eV** & **References** \\ \hline \multirow{4}{*}{La} & \multirow{2}{*}{Dry air} & 300–600 & 0.77 & \multirow{4}{*}{This work} \\ \cline{3-5} \cline{5-5}  & & 600–900 & 1.04 & \\ \cline{3-5} \cline{5-5}  & & 300–600 & 0.66 & \\ \cline{3-5} \cline{5-5}  & & 600–900 & 0.82 & \\ \hline \multirow{3}{*}{Nd} & Dry air & 550–900 & 1.25 & \multirow{3}{*}{[22]} \\ \cline{3-5} \cline{5-5}  & Wet air & 550–900 & 1.16 & \\ \hline \multirow{3}{*}{Sm} & Dry air & 400–900 & 0.74 & \multirow{3}{*}{[16]} \\ \cline{3-5} \cline{5-5}  & Wet air & 400–900 & 0.74 & \\ \hline \multirow{3}{*}{Eu} & Dry air & 400–900 & 1.14 & \multirow{3}{*}{[16]} \\ \cline{3-5} \cline{5-5}  & Wet air & 400–900 & 1.14 & \\ \hline \end{tabular}
\end{table} 
Table 3: Apparent activation energy (E\({}_{\text{a}}\)) of total conductivity temperature dependences of \(Ln_{2}\)(Hf\({}_{1.9}\)Ln\({}_{0.1}\))O\({}_{6.95}\) (Ln = La, Nd, Sm, Eu) stuffed hafnate pyrochlores in dry and wet air. DSC and TG Characterization of La\({}_{2}\)(Hf\({}_{1.9}\)La\({}_{0.1}\))O\({}_{6.95}\)\"Stuffed\" Pyrochlore  
No significant proton conductivity for the \(Ln_{2}\)(Hf\({}_{1.9}\)_La\({}_{0.1}\))O\({}_{6.95}\) (\(Ln\) = Sm, Eu) materials is attributed to the low basicity of Sm\({}_{2}\)O\({}_{3}\) and Eu\({}_{2}\)O\({}_{3}\) and the low hydration degree of oxygen vacancies in position 48f in their pyrochlore solid solutions compared to La- and Nd-counterparts [39]. The La\({}_{2}\)(Hf\({}_{1.9}\)La\({}_{0.1}\))O\({}_{6.95}\) \"stuffed\" pyrochlore powder was heated twice up to 1000 \({}^{\circ}\)C. Figure 4a shows DSC and TG curves of this sample during the first (curves 1 and 1a) and second (curves 2 and 2a) heating cycles. The total weight loss between 50 and 1000 \({}^{\circ}\)C is 0.41% in the first and 0.32% in the second heating cycles. The TG curve obtained during the first heating has two steps. A sharpest weight loss is observed between 50 and 650 \({}^{\circ}\)C, with \(\Delta\)M\({}_{1}\) = 0.33%. According to [PERSON] [40], this temperature range corresponds to the removal of surface water and hydroxyl ions. Above 650 \({}^{\circ}\)C, water was removed rather slowly, up to 1000 \({}^{\circ}\)C. This weight loss is related to the structurally bounded water and interstitial protons [40]. The weight loss was about \(\Delta\)M\({}_{1}\) = 0.08% at 650-1000 \({}^{\circ}\)C. After cooling in the same oxygen atmosphere, the sample was reheated, and the weight loss between 50 and 650 \({}^{\circ}\)C was 0.27%, i.e., smaller than in the first heating cycle. The slope of the second weight loss step, between 650 and 1000 \({}^{\circ}\)C, also decreased, and the weight loss was \(\Delta\)M\({}_{1}\) = 0.05%, i.e., also smaller than in the first heating cycle. Thus, the second heating showed that, during cooling in an oxygen atmosphere, the material regained most of the physically and structurally bound water.