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Indexed by:期刊论文

Date of Publication:2017-02-28

Journal:JOURNAL OF APPLIED PHYSICS

Included Journals:SCIE、EI

Volume:121

Issue:8

ISSN No.:0021-8979

Abstract:To develop Si structures for multifunctional applications, here we proposed four new low-density silicon clathrates ( Si-CL-A, Si-CL-B, Si-CL-C, and Si-CL-D) based on the same bonding topologies of clathrate hydrates. The electronic and thermal properties have been revealed by first-principles calculations. By computing their equation of states, phonon dispersion, and elastic constants, the thermodynamic, dynamic, and mechanical stabilities of Si-CL-A, Si-CL-B, Si-CL-C, and Si-CL-D allotropes are confirmed. In the low-density region of the phase diagram, Si-CL-B, Si-CL-D, and SiCL-C would overtake diamond silicon and type II clathrate ( Si-CL-II) and emerge as the most stable Si allotropes successively. Among them, the two direct semiconductors with bandgaps of 1.147 eV ( Si-CL-A) and 1.086 eV ( Si-CL-D) are found. The suitable bandgaps close to the optimal ShockleyQueisser limit result in better absorption efficiency in solar spectrum than conventional diamond silicon. Owing to the unique cage-based framework, the thermal conductivity of these Si allotropes at room temperature are very low ( 2.7-5.7Wm(-1) K-1), which are lower than that of diamond structured Si by two orders of magnitude. The suitable bandgaps, small effective masses, and low thermal conductivity of our new silicon allotropes are anticipated to find applications in photovoltaic and thermoelectric devices.