Selective reduction of layers at low temperature in artificial superlattice thin films

Abstract

Reduction and oxidation in transition-metal oxides are keys to develop technologies related to energy and the environment. Here we report the selective topochemical reduction observed when artificial superlattices with transition-metal oxides are treated at a temperature below 300 °C with CaH 2. [CaFeO 2] m/[SrTiO 3] n infinite-layer/perovskite artificial superlattice thin films were obtained by low-temperature reduction of [CaFeO 2.5] m/[SrTiO 3[ n brownmillerite/perovskite artificial superlattice thin films. By the reduction only the CaFeO 2.5 layers in the artificial superlattices were reduced to the CaFeO 2 infinite layers whereas the SrTiO 3 layers were unchanged. The observed low-temperature reduction behaviors strongly suggest that the oxygen ion diffusion in the artificial superlattices is confined within the two-dimensional brownmillerite layers. The reduced artificial superlattice could be reoxidized, and thus, the selective reduction and oxidation of the constituent layers in the perovskite-structure framework occur reversibly.