# Novel Highly Dispersed Additive for Proton-Conducting Composites
## 2 Materials and Methods
### Characterization  
The microstructure and phase composition of the samples were determined by X-ray diffraction (XRD). X-ray diffraction patterns were recorded at room temperature using a Bruker D8 Advance diffractometer with CuK\(\alpha\) radiation in the 2\(\theta\) range from 10 to 70\({}^{\circ}\). The phases formed in the system were identified using the Crystallographica Search-Match, Version 2.1 program and the PDF4 database. The average crystallite size was estimated from diffraction line broadening in X-ray diffraction patterns using the Scherer formula  
\[d=\frac{k\lambda}{\beta cos\theta} \tag{1}\]  
where \(d\) is the average crystallite size, \(\lambda\) is the X-ray wavelength (1.54051 A), \(\beta\) is the full width at half maximum of the diffraction peak, \(\theta\) is the diffraction angle, and \(k\) = 0.9. Thermal analysis (TA) of the dried powders was performed on a NETZSCH Jupiter 449C STA synchronous thermal analyzer coupled to QMS 403C Aeolos (TG-QMS) mass spectrometer in an argon flow at temperatures in the range of 20-700 \({}^{\circ}\)C at a heating rate of 10 \({}^{\circ}\)C/min. The microstructure of the samples was studied by field emission scanning electron microscopy (SEM) using Hitachi SU8000 electron microscope (Tokyo, Japan). The images were taken in the secondary electron recording mode at an accelerating voltage of 2-30 kV and a working distance of 8-10 mm. The sample's X-ray energy dispersive spectra (EDS) were measured with the use of an Oxford Instruments add-on for electron microscope. Analytical measurements of the EDS were optimized using a previously established method, as outlined in the references [52; 59]. Prior to the measurements, the samples were affixed to an aluminum mount with a 25 mm diameter and secured firmly with conductive graphite adhesive tape. Additionally, the morphology of the unmodified samples was studied to preclude any surface effects due to the application of the conductive layer, as noted in [60]. The specific surface area was determined by analyzing the BET isotherms  
Figure 1: Synthesis scheme of the precursor.  
of low-temperature nitrogen adsorption at 77 K using a Quantachrome Nova 1000e static instrument. The pore size distribution was calculated using the Barrett-Joyner-Halenda (BJH) method. The proton conductivity of the composites in the (1-\(x\))CsH\({}_{2}\)PO\({}_{4}\)-\(x\)ZnSnO\({}_{3}\) (\(x\) = 0.2, 0.4, 0.6, 0.8) system was measured using a two-electrode circuit on alternating current with an Instek LCR-821 impedance meter (12-200 kHz frequency range) and an IPU-1 RLC-1/2008 precision electrochemical meter (1 Hz-3.3 MHz frequency range). The composites of the specific compositions were synthesized by thoroughly mixing the components in an agate mortar and heating the pelletized samples at 230-240 \({}^{\circ}\)C. Pellets of 6 mm in diameter and 1-1.5 mm thick were pressed from the samples to measure the electrical conductivity, using a pressure of 30-50 MPa. The electrical conductivity of the samples with deposited silver electrodes was measured under cooling conditions at a rate of 1-2 \({}^{\circ}\)C/min in an atmosphere with a high water vapor content (10%, 20%, and 30% molar ratio) in the temperature range of 170-250 \({}^{\circ}\)C, followed by cooling in air with a relative humidity of 40% [48; 52].