506 / 2019-03-19 09:26:18

First-principles Investigations on Metallic Silicon Allotropes

Metallic silicon; First-principles; High density silicon; Structural transition

全体主题 > High Pressure Physics and Materials Science

Diamond-structured Si-I phase is the fundamental material for modern electronics and photovoltaic applications. Small changes in the crystal structure of Si may have a profound influence on its electronic properties, to further expand the application fields of silicon. In the previous research, a large number of semiconductor Si allotropes were predicted or synthesized at ambient pressures. Recently, a tunnel-type metallic silicon allotrope was proposed and named as m-Si20. However, due to the high energy, it may be difficult to synthesize m-Si20 in the lab. So, new metallic Si allotropes with low energy and high stability need to be discovered immediately.
Here, a new metallic metastable silicon allotrope hP12-Si has been proposed theoretically using the particle swarm optimization method. Its stability was verified by calculating its elastic constants and phonon spectrum. The analysis of structural heritability and thermodynamic stability shows that hP12-Si might be obtained by removing Li atoms from the pre-synthetic LiSi12 precursor, which is analogous with the recent preparation of Si24 (fig.1). There are 50% five coordinated silicon atoms, whereas the others are four coordinated in the hP12-Si structure. Electronic band structure calculation indicated that this structure possesses metallic property, which might be due to the delocalization of valence electrons caused by the existence of five coordinated atoms. The current study may enrich the common understanding of metallic silicon, and provides an alternative and significant pathway to achieve novel Si metastable phases through a pre-synthetic high-pressure precursor.
Keywords: Metallic silicon; First-principles; High density silicon; Structural transition