Liu Zhao, Li Da, Liu Yan, Cui Tian, Tian Fubo, Duan Defang
State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun, 130012, People's Republic of China.
Phys Chem Chem Phys. 2019 Jun 5;21(22):12029-12035. doi: 10.1039/c9cp01723b.
High pressure can stimulate numerous novel physical effects which are not observed under ambient conditions, such as the electronic redistribution and delocalization phenomenon in strongly covalently bonded nitrides. Through first principles simulations, we report a new N-rich aluminum nitride AlN5, which crystallizes with the space group P1[combining macron] at 20 GPa and then transforms into the I4[combining macron]2d phase at 60 GPa. We have identified and proved the delocalization effects of π electrons in the strongly covalent Lewis poly-nitrogen structure via the one-dimensional particle in a box mechanism, which contributes to the metallization and stability of the system. This implies that not all strongly covalently bonded systems with highly localized electrons exhibit nonmetallic properties in III-V main group nitrides. Furthermore, pressure results in the hybridization configuration mutation from sp2 in the P1[combining macron] phase to a mixture of sp2 and sp3 hybridization in the I4[combining macron]2d phase, which leads to phase transition from metal to insulator. With increasing pressure, the band gap increases abnormally, exhibiting anti-metallization induced by the strong hybridization. Interestingly, the P1[combining macron] and I4[combining macron]2d structures are simultaneously accompanied by a high energy density and hardness, which enable them to have a greater ability to resist elasticity, plastic deformation and external force destruction in potential applications. Their energy density and hardness are up to 3.29 kJ g-1 and 15.2 GPa in the P1[combining macron] phase but especially 6.14 kJ g-1 and 31.7 GPa in the I4[combining macron]2d phase.
高压能够激发许多在常压条件下未被观测到的新奇物理效应，比如强共价键氮化物中的电子重新分布和离域现象。通过第一性原理模拟，我们报道了一种新型富氮氮化铝AlN5，它在20 GPa下以P1[上加一横]空间群结晶，然后在60 GPa时转变为I4[上加一横]2d相。我们通过一维盒中粒子机制识别并证明了强共价路易斯多氮结构中π电子的离域效应，这有助于体系的金属化和稳定性。这意味着并非所有具有高度局域化电子的强共价键体系在III-V主族氮化物中都表现出非金属特性。此外，压力导致杂化构型从P1[上加一横]相中的sp2杂化转变为I4[上加一横]2d相中的sp2和sp3杂化混合，这导致了从金属到绝缘体的相变。随着压力增加，带隙异常增大，表现出由强杂化引起的反金属化。有趣的是，P1[上加一横]和I4[上加一横]2d结构同时伴随着高能量密度和硬度，这使得它们在潜在应用中具有更强的抵抗弹性、塑性变形和外力破坏的能力。它们在P1[上加一横]相中的能量密度和硬度分别高达3.29 kJ g-1和15.2 GPa，但在I4[上加一横]2d相中尤其高达6.14 kJ g-1和31.7 GPa。
