Hasegawa Takuya, Yamasaki Naoki, Asakura Yusuke, Ueda Tadaharu, Yin Shu
Institute of Multidisciplinary Research for Advanced Material (IMRAM), Tohoku University 2-1-1 Katahira, Aoba-ku Sendai 980-8577 Japan
Department of Marine Resource Science, Faculty of Agriculture and Marine Science, Kochi University Nankoku 783-8502 Japan.
Chem Sci. 2021 Oct 15;12(45):15016-15027. doi: 10.1039/d1sc03053a. eCollection 2021 Nov 24.
Layered perovskites have been extensively investigated in many research fields, such as electronics, catalysis, optics, energy, and magnetics, because of the fascinating chemical properties that are generated by the specific structural features of perovskite frameworks. Furthermore, the interlayers of these structures can be chemically modified through ion exchange to form nanosheets. To further expand the modification of layered perovskites, we have demonstrated an advance in the new structural concept of layered perovskite "charge-neutral perovskite layers" by manipulating the perovskite layer itself. A charge-neutral perovskite layer in [CeTaO] was synthesized through a soft chemical oxidative reaction based on anionic [CeTaO] layers. The Ce oxidation state for the charge-neutral [CeTaO] layers was found to be tetravalent by X-ray absorption fine structure (XAFS) analysis. The atomic arrangements were determined through scattering transmission electron microscopy and extended XAFS (EXAFS) analysis. The framework structure was simulated through density functional theory (DFT) calculations, the results of which were in good agreement with those of the EXAFS spectra quantitative analysis. The anionic [CeTaO] layers exhibited optical absorption in the near infrared (NIR) region at approximately 1000 nm, whereas the level of NIR absorption decreased in the [CeTaO] charge-neutral layer due to the disappearance of the Ce 4f electrons. In addition, the chemical reactivity of the charge-neutral [CeTaO] layers was investigated by chemical reduction with ascorbic acid, resulting in the reduction of the [CeTaO] layers to form anionic [CeTaO] layers. Furthermore, the anionic [CeTaO] layers exhibited redox activity which the Ce in the perovskite unit can be electrochemically oxidized and reduced. The synthesis of the "charge-neutral" perovskite layer indicated that diverse features were generated by systematically tuning the electronic structure through the redox control of Ce; such diverse features have not been found in conventional layered perovskites. This study could demonstrate the potential for developing innovative, unique functional materials with perovskite structures.
层状钙钛矿因其钙钛矿骨架的特定结构特征所产生的迷人化学性质，已在电子学、催化、光学、能源和磁学等众多研究领域得到广泛研究。此外，这些结构的中间层可通过离子交换进行化学修饰以形成纳米片。为了进一步扩展层状钙钛矿的修饰，我们通过操控钙钛矿层本身，在层状钙钛矿“电荷中性钙钛矿层”这一新结构概念方面取得了进展。基于阴离子[CeTaO]层，通过软化学氧化反应合成了[CeTaO]中的电荷中性钙钛矿层。通过X射线吸收精细结构（XAFS）分析发现，电荷中性[CeTaO]层的Ce氧化态为四价。通过散射透射电子显微镜和扩展XAFS（EXAFS）分析确定了原子排列。通过密度泛函理论（DFT）计算对骨架结构进行了模拟，其结果与EXAFS光谱定量分析结果吻合良好。阴离子[CeTaO]层在近红外（NIR）区域约1000 nm处表现出光吸收，而由于Ce 4f电子的消失，[CeTaO]电荷中性层中的近红外吸收水平降低。此外，通过用抗坏血酸进行化学还原研究了电荷中性[CeTaO]层的化学反应性，导致[CeTaO]层还原形成阴离子[CeTaO]层。此外，阴离子[CeTaO]层表现出氧化还原活性，钙钛矿单元中的Ce可被电化学氧化和还原。“电荷中性”钙钛矿层的合成表明，通过Ce的氧化还原控制系统地调节电子结构会产生多种特性；在传统层状钙钛矿中尚未发现此类多样的特性。这项研究可以证明开发具有钙钛矿结构的创新、独特功能材料的潜力。
