Crystal structure and ion transport properties of solid electrolyte CsAg₄Br_3-xI_2+x (0 < x < 1)

Silver-based ionic conductive materials have attracted much interest due to their potential application in the solid electrolyte ion sources (SEIS) in ionic thrusters. In this work, a mechano-chemical synthesis process was developed for preparation of crystalline superionic conductors CsAg₄Br_3-xI_2+x (0 < x < 1) in Ar atmosphere. The crystal structure, morphology, and elemental composition of the silver-based solid electrolytes were investigated. The alternating current (AC) impedance spectroscopy was applied to study the ionic conductivity of CsAg₄Br_3-xI_2+x (x = 0.25), which had a highest value of 0.13 S/cm at 25 °C with low activation energies of 0.148 eV. The grain size of CsAg₄Br_3-xI_2+x was distributed in the range of 0.2–1.0 μm as observed by scanning electron microscopy. We found that the sample with x = 0.25 could be sustained for 18 months in air atmosphere with good chemical stabilities as compared with other samples. We also discuss on the role of key factors in the ionic conductivity, giving reasonable interpretation of the influence of the crystal structure and elemental composition on the ionic transport of the solid electrolyte CsAg₄Br_3-xI_2+x (0 < x < 1).