Department of Chemistry, Faculty of Science and Graduate School of Science, Tohoku University

Reversible switching of room-temperature electrical resistivity due to crystal-amorphous transition is demonstrated in various chalcogenides for development of non-volatile phase change memory. However, such reversible thermal switching of room-temperature electrical resistivity has not been reported in transition metal oxides so far, despite their enormous studies on the electrical conduction like metal-insulator transition and colossal magnetoresistance effect. In our group, a thermally reversible switching of room-temperature electrical resistivity is reported with gigantic variation in a layered nickelate Sr_2.5Bi_0.5NiO₅ composed of (Sr_1.5Bi_0.5)O₂ rock-salt and SrNiO₃ perovskite layers via unique crystalline phase changes between the conducting Sr_2.5Bi_0.5NiO₅ with ordered (order phase), disordered Sr/Bi arrangements in the (Sr_1.5Bi_0.5)O₂ layer (disorder phase), and insulating double perovskite Sr₂BiNiO_4.5. The order phase is reentrant by high-temperature annealing of around 1000℃ through crystalline phase change into the disorder phase and double perovskite, resulting in the thermally reversible switching of room-temperature electrical resistivity with 10²- and 10⁹-fold variation, respectively. The Sr_2.5Bi_0.5NiO₅ is the first oxide to show the thermally reversible switching of room-temperature electrical resistivity via the crystalline phase changes, providing a new perspective on not only the electrical conduction for transition metal oxides but also oxide-based phase change memory.