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478Compounds with proton conductivity have been of a special interest for researchers due to their high potential for use as materials for electrolytes (mem branes) of fuel cells [1].Today, fuel cells compare favorably with the energy sources in current use in terms of their high efficiency, as well as environmental and operational safety.The qualifying standards for the fuel cell materials are diverse due to the diversity of their performance. In other words, there are no rigid limits for temperature parameters or the physical state of the material. Ionic transport with adequate conductivity is the major requirement. Compoundswith the general formula M m H n (AO 4 ) (m + n)/2 ⋅ xH 2 O (M = K, NH 4 , Rb, Cs; A = S, Se, P) are an example of these materials [2]. Con ductors based on cesium hydrogen salts, mostly, on cesium hydrophosphates and hydrosulfates, have recently been of special interest. Single crystals of CsH 2 PO 4 , CsHSO 4 , and complex hydrosulfatophos phates Cs 2 (HSO 4 )(H 2 PO 4 ), α(β) Cs 3 (HSO 4 ) 2 (H 2 PO 4 ) and Cs 5 (HSO 4 ) 3 (H 2 PO 4 ) 2 have been prepared [3][4][5][6][7][8][9]. Superionic transition temperatures were determined for some of these compounds.This study presents the results of synthesis and characterization of complex cesium hydrosulfato phosphates. The CsH 2 PO 4 -CsHSO 4 -H 2 O ternary system was studied at 25.0°С over the entire concen tration range using an isothermal method to investi gate the interaction between the initial components (CsH 2 PO 4 and CsHSO 4 ). Single crystals of the result ing phases were grown and analyzed. EXPERIMENTAL Cesium hydrosulfate CsHSO 4 (high purity grade, technical specifications TU 6 09 04 198 83) and cesium dihydrophosphate CsH 2 PO 4 (high purity grade, technical specifications TU 6 09 04 201 82) were used to study the interaction between the compo nents of the CsHSO 4 -CsH 2 PO 4 -H 2 O system and to grow single crystal samples. Cesium in the liquid phase and the solid residue was determined gravimet rically as cesium tetraphenylborate [10]; phosphate anion was determined photocolorimetrically [11].X ray diffraction analysis was carried out on an XRD 6000 Shimadzu diffractometer (bent graphite monochromator, CuK α on a diffracted beam, contin uous scan mode 1 deg/min, increment 0.02° over the 2θ angle range of 10°-80°, no sample rotation).The elemental analysis of single crystal samples was carried out on a Quanta 200 3D atomic force microscope using energy dispersive X ray analysis (EDAX) according to the standard absorption coeffi cients; a CsH 2 PO 4 (CDP) single crystal was used as the reference; tube voltage was 15 kV; scanning time 500 s; refinement using the ZAF system.Intercomponent interactions in the CsHSO 4 -CsH 2 PO 4 -H 2 O system were studied under isothermal equilibrium conditions at 25.0°С. Temperature was maintained constant using a thermostat; the time required to attain equilibrium was 24 h.Weighed portions of the compounds were placed into 50 mL round bottom flasks and kept in the ther mostat; stirring was provided...

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