Mechano-chemical Synthesis of RbAg₄I₅ and KAg₄I₅ Crystals and Their Silver lon Conducting Properties

Abstract

A high-energy-ball-milling process was applied to the synthesis of the RbAg₄I₅ and KAg₄I₅ crystalline phases, which were known to show high Ag⁺ ion conductivity 2.7×10¹ Sm^-1 at room temperature. RbI, KI, and AgI were used as raw materials for the mechanical synthesis of the RbAg₄I₅ and KAg₄I₅ phases. Only 20min-ball milling of a mixture of RbI and AgI led to the formation of RbAg₄I₅ phase, and the powder sample after 140 min-ball milling was containing only RbAg₄I₅ phase. On the other hand, the preparation of the sample containing only KAg₄I₅ phase needed the ball-mill treatment more than 50h.The obtained RbAg₄I₅ and KAg₄I₅ samples showed high ion conductivity more than 10¹ Sm^-1 at room temperature, and the conductivities were almost same as those of the RbAg₄I₅ and KAg₄I₅ crystalline phases reported by Owens et al. The DC polarization measurements suggested that main carrier of the ball-milled samples was silver ions and the silver ion transport numbers of the ball-milled samples were almost unity.