# Novel Highly Dispersed Additive for Proton-Conducting Composites
## 3 Results and Discussion  
The results from the atomic emission spectrometry analysis showed the minimal residual content of zinc (less 0.1 \(\upmu\)g/mL) and tin (less than 0.2 \(\upmu\)g/mL) in the mother solution. This indicates that the reaction (2) went to completion, yielding a precipitate with a stoichiometric ratio of Zn:Sn = 1:1. XRD data revealed that the chemical co-precipitation resulted in the formation of zinc hexahydroxostannate ZnSn(OH)\({}_{6}\), which possesses a visminrovite structure with a cubic unit cell and symmetry, space group Pn3m, similar to schoenfliesite [61; 62]. The diffraction pattern of the sample is shown in Figure 2 (curve 1). The value of the lattice parameter, determined using the Rietveld method with Powder Cell 2.4 software, was a = 0.77647 \(\pm\) 0.00084 nm, and was in good agreement with literature data (a = 0.78 nm [39; 62], PDF4, card no. 73-2384). The following reaction results in the formation of ZnSn(OH)\({}_{6}\):  
\[\mathrm{ZnCl_{2}+Na_{2}Sn(OH)_{6}\to ZnSn(OH)_{6}+2\ NaCl} \tag{2}\]  
According to scanning electron microscopy data (Figure 3a), the freshly deposited ZnSn(OH)\({}_{6}\) samples were cubic well-grained single crystals of 150-250 nm in size. According to the results of the chemical microanalysis carried out by the EDS method, the  
Figure 2: X-ray diffraction patterns of initial ZnSn(OH)\({}_{6}\) (1) and thermolysis products obtained at temperatures of 300–520 \({}^{\circ}\)C (2), 600 \({}^{\circ}\)C (3), and 700 \({}^{\circ}\)C (4). Zn:Sn:O atomic ratio fell within the range of (10 \(\pm\) 1):(10 \(\pm\) 1):(63 \(\pm\) 3), which was close to the stoichiometric ratio for ZnSn(OH)\({}_{6}\). According to the thermal analysis data (Figure 4), when ZnSn(OH)\({}_{6}\) is heated, successive processes occur, accompanied by changes in the mass, structure, and phase composition, which are consistent with the XRD results. A weight loss of about 18.7% was observed when the sample was heated to a temperature between 50-520 \({}^{\circ}\)C, which quantitatively agreed with the calculated value (18.87%) for the reaction:  
\[\text{ZnSn(OH)}_{6}\rightarrow\text{ZnSnO}_{3}+3\text{ H}_{2}\text{O} \tag{3}\]  
The reaction was accompanied by an endothermic effect with a maximum at T\({}_{\text{max}}\) = 268 \({}^{\circ}\)C.  
According to XRD data, heating ZnSn(OH)\({}_{6}\) at 300-520 \({}^{\circ}\)C for 4 h produced X-ray amorphous zinc stannate (Figure 2, curve 2). Scanning electron microscopy showed that the dehydrated product was a pseudomorphosis made of nanoparticles of the amorphous phase, retaining the shape and size of the original particles (Figure 3b). At 540-600 \({}^{\circ}\)C, an exothermic effect was observed, likely indicating the formation of a weakly crystallized ZnSnO\({}_{3}\) phase with a perovskite structure (card 28-1486, PDF4), with the particle size estimated at being 15-20 nm using the Scherrer equation (Figure 2, curve 3). Zinc metastan  
Figure 4: Synchronous thermal analysis curves obtained during the thermal decomposition of a ZnSn(OH)\({}_{6}\) sample: mass change (TG), thermal effects (DSC), and the ionic current of the mass spectrometer measured for the atomic mass number \(m/z\) of 18 amu corresponding to water molecules evolving from the sample. Figure 3: SEM images of freshly deposited ZnSn(OH)\({}_{6}\) (**a**) and after its calcination at 520 \({}^{\circ}\)C (**b**) and 700 \({}^{\circ}\)C (**c**). nate is metastable, and the transition to the stable phase Zn\({}_{2}\)SnO\({}_{4}\) with a spinel structure occurred at temperatures above 700 \({}^{\circ}\)C, in accordance with the reaction:  
\[2\ \text{ZnSnO}_{3}\to\text{Zn}_{2}\text{SnO}_{4}+\text{SnO}_{2} \tag{4}\]  
The annealing at 700 \({}^{\circ}\)C resulted in the decomposition of the ZnSnO\({}_{3}\) phase into a mixture of the nanocrystalline SnO\({}_{2}\) phase with the cassiterite structure (card 71-652, PDF4) and the Zn\({}_{2}\)SnO\({}_{4}\) phase with the spinel structure (card 74-2184, PDF4) (Figure 2, curve 4).