# Novel Highly Dispersed Additive for Proton-Conducting Composites
## 3 Results and Discussion
Using the Scherrer equation, the estimated size of the nanocomposite particles was less than 60-70 nm for zinc stannate Zn\({}_{2}\)SnO\({}_{4}\) and 20-40 nm for tin dioxide. Scanning electron microscopy showed that the pseudomorphosis of the nanoparticle aggregate was preserved (Figure 3c). However, the large cubic aggregates consisted of the weakly aggregated Zn\({}_{2}\)SnO\({}_{4}\) nanoparticles surrounded by the smaller particles of tin dioxide visible on the surface of the cubic aggregates. The FTIR spectra analysis of ZnSn(OH)\({}_{6}\) and its synthesized compounds showed the structural features and composition, with the characteristic bands assigned based on published data [63,64]. The FTIR spectra of the obtained zinc hydroxtannate ZnSn(OH)\({}_{6}\) and zinc stannate ZnSnO\({}_{3}\) samples (Figure 5a) matched previous studies [29,49,65]. In the spectra, a wide band of \(\
u\)(OH) stretching vibrations in the 3100-3300 cm\({}^{-1}\) region indicated the presence of hydroxyl groups in the precursor and a system of hydrogen bonds in the compound structure. The absorption band at 1180 cm\({}^{-1}\) was due to bending vibrations of the Sn-OH bonds, and the moisture deformation vibrations were recorded above 1630 cm\({}^{-1}\). These bands decreased with the sample's dehydration during the heat treatment at 600 \({}^{\circ}\)C, which was consistent with the weight loss according to the TG results. In the region of the metal-oxygen bonds (900-400 cm\({}^{-1}\)) of ZnSnO\({}_{3}\), the FTIR spectra showed a strong band at 615 cm\({}^{-1}\), corresponding to the symmetric stretching vibrations of the Sn-O bonds (Figure 4a). After holding ZnSnO\({}_{3}\) in the air, a broad diffuse absorption band between 3250-3650 cm\({}^{-1}\), corresponding to hydrogen bonds and associated with the stretching vibrations \(\
u\)(H\({}_{2}\)O), confirmed the sorption of water vapor. The data of the thermal analysis (Figure 5b) for the sample after storage suggested the absorption of water, approximately up to 0.2 mole of H\({}_{2}\)O, per mole of zinc stannate. The results indicate the reversible sorption of ZnSnO\({}_{3}\) water vapor in air and its desorption at elevated  
Figure 5: (**a**) FTIR spectra of ZnSn(OH)\({}_{6}\) (I) and ZnSnO\({}_{3}\) obtained by the thermolysis of ZnSn(OH)\({}_{6}\) (2) and kept in air for some time (3). (**b**) Dependence of mass change (TG) of a ZnSnO\({}_{3}\) sample after storage in an air atmosphere of a desiccator. temperatures. Similar to ZnSn(OH)\({}_{6}\), ZnSnO\({}_{3}\) was characterized by the presence of strongly bound adsorbed water molecules. Table 1 presents the textural properties, specific surface area, and mean pore size of the initial samples and samples calcined at different temperatures for 4 h. High specific surface area values and the presence of mesopores with sizes around 6 nm were characteristics of the samples created during the thermolysis of ZnSn(OH)\({}_{6}\). As the heating temperature increased, the specific surface area values monotonically decreased while the pore sizes increased. As seen from Table 1, the amorphous zinc stannate, obtained by heating at 520 \({}^{\circ}\)C, had a higher specific surface area. This high-surface-area zinc stannate, with increased water retention, was used as a heterogeneous additive for CsH\({}_{2}\)PO\({}_{4}\). The proton conductivity and structural properties of the (1-\(x\))CsH\({}_{2}\)PO\({}_{4}\)-\(x\)ZnSnO\({}_{3}\) composite system were studied across a range of compositions (\(x\) = 0.2-0.8). The XRD patterns indicated no chemical interaction between the components, and the crystalline structure of CsH\({}_{2}\)PO\({}_{4}\) was preserved. The intensity of the reflections corresponding to the LT phase of CsH\({}_{2}\)PO\({}_{4}\) (P2/1m) decreased significantly more than the salt content in the composite (Figure 6a), resulting in a disordered state of CsH\({}_{2}\)PO\({}_{4}\).