State Key Lab of Superhard Materials, College of Physics, Jilin University , Changchun 130012, China.
Beijing Computational Science Research Center , Beijing 100084, China.
J Am Chem Soc. 2017 Oct 4;139(39):13798-13803. doi: 10.1021/jacs.7b07016. Epub 2017 Sep 22.
High pressure is able to modify profoundly the chemical bonding and generate new phase structures of materials with chemical and physical properties not accessible at ambient conditions. We here report an unprecedented phenomenon on the pressure-induced formation of semiconducting electrides via compression of layered alkaline-earth subnitrides CaN, SrN, and BaN that are conducting electrides with loosely confined electrons in the interlayer voids at ambient pressure. Our extensive first-principles swarm structure searches identified the high-pressure semiconducting electride phases of a tetragonal I4̅2d structure for CaN and a monoclinic Cc structure shared by SrN and BaN, both of which contain atomic-size cavities with paring electrons distributed within. These electride structures are validated by the excellent agreement between the simulated X-ray diffraction patterns and the experimental data available. We attribute the emergence of the semiconducting electride phases to the p-d hybridization on alkaline-earth-metal atoms under compression as well as the filling of the p-d hybridized band due to the interaction between Ca and N. Our work provides a unique example of pressure-induced metal-to-semiconductor transition in compound materials and reveals unambiguously the electron-confinement topology change between different types of electrides.
高压能够深刻地改变化学键，并生成具有在环境条件下无法获得的化学和物理性质的新材料的相结构。我们在这里报告了一个前所未有的现象，即在压缩层状碱土亚氮化物 CaN、SrN 和 BaN 时，通过压力诱导形成半导体电子化物，这些电子化物在环境压力下在层间空隙中具有松散束缚的电子，是导电电子化物。我们广泛的第一性原理群体结构搜索确定了 CaN 的四方 I4̅2d 结构和 SrN 和 BaN 共有的单斜 Cc 结构的高压半导体电子化物相，这两种结构都包含具有配对电子分布的原子大小的空腔。这些电子化物结构通过模拟 X 射线衍射图谱与现有实验数据之间的优异一致性得到验证。我们将半导体电子化物相的出现归因于压缩下碱土金属原子上的 p-d 杂化以及由于 Ca 和 N 之间的相互作用导致 p-d 杂化带的填充。我们的工作提供了化合物材料中压力诱导的金属-半导体转变的独特范例，并清楚地揭示了不同类型电子化物之间电子束缚拓扑结构的变化。
