Evidence for enormous iodide anion migration in lanthanum oxyiodide–based solid

The I(−) ion conduction was demonstrated and quantified in the La(0.70)Sr(0.25)Zn(0.05)OI(0.70) solid. The I(−) ion is considered to be an inferior conductor because of its large ionic size compared to the previously reported conducting ion species. Using modified Tubandt electrolysis, a weight increase at the anodic pellet and a corresponding weight decrease at the cathodic pellet were observed. The weight changes were in good agreement with the theoretical values estimated by considering pure I(−) ion migration. Furthermore, the iodine element appeared at the anode, and the iodine concentration at the cathode decreased after electrolysis, indicating that the migrating species was only I(−). This is the first study to elucidate the conduction of iodide ions in solids.