[25a-F307-1~8] 6.4 Thin films and New materials

▲ [25a-F307-4] Discovery of highly reduced oxide SrCoO₂ via electrochemical proton reduction and dehydration

〇Haobo Li^1,3, Shunsuke Kobayashi², Chengchao Zhong³, Morito Namba³, Yu Cao³, Daichi Kato³, Yoshinori Kotani⁴, Qianmei Lin³, Maokun Wu⁵, Wei-Hua Wang⁵, Masaki Kobayashi³, Koji Fujita³, Cedric Tassel³, Takahito Terashima³, Akihide Kuwabara², Yoji Kobayashi³, Hiroshi Takatsu³, Hiroshi Kageyama³ (1.Osaka Univ. SANKEN, 2.JFCC, 3.Kyoto Univ., 4.SPring-8, 5.Nankai Univ.)

Keywords:strongly correlated oxide, thin film, ionic liquid gating

Controlling oxygen deficiencies is essential for the development of novel chemical and physical properties in strongly correlated oxides. In the recent dedaces, low-temperature topochemical reactions using metal hydrides (e.g., CaH₂) are known as a powerful method to lead to highly reduced oxides such as SrFeO₂ and LaNiO₂ although their applicability is limited due to uncontrollable product. In this work we use a combination of electrochemical protonation and thermal dehydration to synthesize highly reduced oxide. SrCoO_2.5 thin film is converted to SrCoO₂ by dehydration of HSrCoO_2.5 at 350 °C (Figure 1). SrCoO₂ represents the first perovskite-derived compound consisting only of tetrahedra, forming a four-legged spin tube. Upon heating, HSrCoO_2.5 with distorted octahedra gradually dehydrates (H_1-xCoO_2.5–x/2) and then switches to the one-dimensional spin tube structure. This suggests that ‘destabilization’ of the SrCoO_2.5 precursor by protonation drastically alters the reaction energy landscape. Given that electrochemical protonation has been applied to a variety of transition metal oxides, this simple process opens new avenues for exploring novel oxides.