Structure and Electrons in Mayenite Electrides

One major goal in materials chemistry is to find inexpensive compounds with improved capabilities. Stable inorganic electrides, derived from nanoporous mayenite [Ca12Al14O32]O, are a new family that has very interesting properties such as electronic conductivity combined with transparency. However, an intriguing fundamental problem is to understand the structures of these cubic materials and to characterize their free-electron loadings. Here we report an accurate structural study for three members of the series [Ca12Al14O32]O1−δe2δ (δ = 0, 0.15, and 0.45), from single-crystal low-temperature synchrotron X-ray diffraction. The complex structural disorder imposed by the presence of the oxide anions into the mayenite cages has been unravelled. Furthermore, the final electron density map for δ = 0.45 black mayenite has shown electron density localized into the center of the cages, which is the first experimental proof of their electride nature. The reported structural findings challenge theorists to improve predictive models in this new family of materials.

材料化学的核心目标之一，在于发掘兼具低廉成本与优化性能的化合物。源自纳米多孔钙铝石（mayenite，[Ca12Al14O32]O）的稳定无机电子化物（electrides）是一类新型材料，其兼具电子导电性与透光性等诸多有趣特性。然而，解析这类立方材料的结构并表征其自由电子负载量，仍是一个引人关注的基础科学问题。本研究依托单晶低温同步辐射X射线衍射技术，对系列化合物[Ca12Al14O32]O1−δe2δ（δ分别为0、0.15和0.45）的三个组分开展了精准结构研究。研究厘清了钙铝石笼腔中氧化物阴离子引入的复杂结构无序现象。此外，针对δ=0.45的黑色钙铝石的最终电子密度图显示，电子密度定域于笼腔中心，这为这类材料的电子化物本质提供了首个实验证据。本研究报道的结构研究成果，将推动理论研究者优化这类新型材料的预测模型。