Amorphous-nonmetal—to—crystalline-metal transition in electrochromic iridium oxide films

Abstract

We report studies of sputtered iridium oxide films (SIROF's) by differential thermal analysis, evolved-gas analysis, scanning electron microscopy, x-ray diffraction, and electrical-conductivity measurements. SIROF's undergo an irreversible exothermic transition at ∼300°C with ∼1 eV energy release and no associated decomposition. There is a second endothermic transition at ∼700°C, which is associated with dehydration. We show that the first transition is an amorphous-to-crystalline transition. The amorphous state is nonmetallic, whereas metallic conductivity is observed in the crystalline state. After undergoing the transition, SIROF's lose their good electrochromic and electrocatalytic properties. We show that these properties are associated with the fast-ion mobility in the amorphous state.