Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.
Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
Nat Chem. 2015 Dec;7(12):1017-23. doi: 10.1038/nchem.2370. Epub 2015 Oct 19.
Oxynitrides have been explored extensively in the past decade because of their interesting properties, such as visible-light absorption, photocatalytic activity and high dielectric permittivity. Their synthesis typically requires high-temperature NH3 treatment (800-1,300 °C) of precursors, such as oxides, but the highly reducing conditions and the low mobility of N(3-) species in the lattice place significant constraints on the composition and structure-and hence the properties-of the resulting oxynitrides. Here we show a topochemical route that enables the preparation of an oxynitride at low temperatures (<500 °C), using a perovskite oxyhydride as a host. The lability of H(-) in BaTiO3-xHx (x ≤ 0.6) allows H(-)/N(3-) exchange to occur, and yields a room-temperature ferroelectric BaTiO3-xN2x/3. This anion exchange is accompanied by a metal-to-insulator crossover via mixed O-H-N intermediates. These findings suggest that this 'labile hydride' strategy can be used to explore various oxynitrides, and perhaps other mixed anionic compounds.
在过去的十年中，由于其有趣的性质，如可见光吸收、光催化活性和高介电常数，氧氮化物得到了广泛的研究。它们的合成通常需要高温 NH3 处理（800-1300°C）前驱体，如氧化物，但高度还原的条件和晶格中 N(3-) 物种的低迁移率对最终氧氮化物的组成和结构，因此也对其性质施加了重大限制。在这里，我们展示了一种拓扑化学途径，可以使用钙钛矿氧氢化物作为主体，在低温（<500°C）下制备氧氮化物。BaTiO3-xHx（x≤0.6）中 H(-)的不稳定性允许 H(-)/N(3-)交换发生，并得到室温铁电 BaTiO3-xN2x/3。这种阴离子交换伴随着通过混合 O-H-N 中间体的金属-绝缘体转变。这些发现表明，这种“不稳定氢化物”策略可用于探索各种氧氮化物，也许还有其他混合阴离子化合物。
