Electrochemical Properties of Superionic Conductors CsAg₄Br_{3 – х}I_{2 + х}

Abstract

Solid solutions CsAg₄Br_{3 – х}I_{2 + х} (x = 0.38; 0.50; 0.68) are prepared by solid-state synthesis; the single phase of the products is confirmed using the methods of X-ray diffraction and differential scanning calorimetry. The studies of electrotransport characteristics of CsAg₄Br_{3 – х}I_{2 + х} involve measuring the ionic conductivity by the four-probe method in the temperature interval from –50 to +120°C and estimating its electronic component by the Hebb–Wagner method. It is shown that in the studied interval of compositions, the ionic conductivity of CsAg₄Br_{3 – х}I_{2 + х} solid solutions is practically independent of x, approaching the conductivity of the well-known superionic conductor RbAg₄I₅. The activation energy of conduction is found to be about 10 kJ mol^–1 for all compounds studied. The oxidation potential determined by the method of stepwise polarization for CsAg₄Br_{3 – х}I_{2 + х} solid solutions is considerably higher as compared with RbAg₄I₅, being in the range of 0.75–0.78 V (vs. Ag⁰/Ag⁺). The high electrochemical characteristics of CsAg₄Br_{3 – х}I_{2 + х} (0.38 ≤ x ≤ 0.63) and the absence of polymorphic transitions in the considered interval from –160°С to the melting point (175–178°С) make these materials promising for the use in electrochemical devices, especially in low-temperature applications.