# Novel Highly Dispersed Additive for Proton-Conducting Composites
## 3 Results and Discussion
The introduction of small amounts of additives significantly increased the conductivity of the composites in the low-temperature region, with specific conductivity values depending on composition. At \(x\) = 0.2, the low  
\begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **190 \({}^{\circ}\)C** & **230 \({}^{\circ}\)C** \\ \hline \(R_{1}\), k\(\Omega\) & 1.97 \(\pm\) 0.09 & 0.176 \(\pm\) 0.004 \\ \hline \(Y_{1}  
temperature conductivity reached a maximum, increasing by 2.5 orders of magnitude. Consequently, the conductivity jump during the superionic phase transition decreased significantly at \(x=0.2\). The increase in the conductivity was due to the disordering and partial amorphization of the salt at the interface between the two phases, which occurred as the fraction of additive increased. However, as \(x\) further increased to 0.4, the conductivity began to decrease (Figure 8a), despite the volume fraction of the heterogeneous component not exceeding 30%. In the case of \(x=0.6\), the conductivity in the low-temperature region sharply decreased to values lower than the initial salt due to the percolation effect. The high-temperature region conductivity decreased almost linearly with an increase in the proportion of additive compared with pure CsH\({}_{2}\)PO\({}_{4}\), due to the \"conductor-insulator\" percolation effect (Figure 8a,b). Nevertheless, with the addition of small amounts of ZnSnO\({}_{3}\), the proton conductivity at high temperatures remained close to the values of the initial salt. In addition, the intro  
Figure 8: Isotherms of the proton conductivity for the composite systems (1–\(x\))CsH\({}_{2}\)PO\({}_{4}\)–\(x\)ZnSnO\({}_{3}\) at different temperatures: 138 \({}^{\circ}\)C (**a**) and 227 \({}^{\circ}\)C (**b**). Figure 7: Temperature dependence of conductivity for composite systems (1–\(x\))CsH\({}_{2}\)PO\({}_{4}\)–\(x\)ZnSnO\({}_{3}\) (\(x=0.2\)–\(0.8\)) in comparison with CsH\({}_{2}\)PO\({}_{4}\) and ZnSnO\({}_{3}\). The conductivity measurement was carried out on two to three pellets with the same composition, but the different size. The relative error in the determining the conductivity is 2–5%. duction of a non-conducting matrix led to an increase in the low-temperature conductivity within a specific range of compositions, but reduced the superprotonic conductivity. The composite effects observed in this system were comparable to the conductivity values seen in the CsH\({}_{2}\)PO\({}_{4}\)-SrZrO\({}_{3}\) and CsH\({}_{2}\)PO\({}_{4}\)-NdPO\({}_{4}\) systems [48, 52], but somewhat lower than for a number of the studied composite systems based on CsH\({}_{2}\)PO\({}_{4}\)[50, 51, 55, 58]. This may be due to an insufficiently high specific surface area and the adhesion energy that determine the interface interaction. Nonetheless, for the samples with the highest proton conductivity values at \(x\) = 0.2, the stability of high conductivity values in the superionic region was maintained even with long-term, isothermal exposure at lower partial pressures of water vapor (10% and 20%) due to the higher water retention of the ZnSSnO\({}_{3}\) matrix. Figure 9 shows the stable conductivity values during the long-term isothermal exposure at the partial water vapor concentration of 10% and 20%, which were lower than those used, in accordance with the phase diagram [43]. The proton conductivity retained unchanged values of 8 \(\times\) 10\({}^{-3}\) S/cm at significantly lower partial pressures of water vapor during 150 min at 230 \({}^{\circ}\)C (Figure 9). This was likely due to the presence of adsorbed water in the ZnSSnO\({}_{3}\) matrix, which was removed at elevated temperatures and prevented dehydration of the CsH\({}_{2}\)PO\({}_{4}\) salt within the composite.