t-Si64 : A Novel Silicon Allotrope

Abstract

Utilizing first principle calculations, a novel Si₆₄ silicon allotrope in the I4₁ /amd space group with tetragonal symmetry (denoted as t-Si₆₄ below) is proposed in this work. In addition, also its structural, anisotropic mechanical, and electronic properties along with its minimum thermal conductivity κ_min were predicted. The mechanical and thermodynamic stability of t-Si₆₄ were evaluated by means of elastic constants and phonon spectra. The electronic band structure indicates that t-Si₆₄ is an indirect band gap semiconductor with a band gap: 0.67 eV (primitive cell) compared to a direct band gap of 0.70 eV with respect to a conventional cell. The minimum thermal conductivity of t-Si₆₄ (0.74 W cm^-1 K^-1 ) is much smaller than that of diamond silicon (1.13 W cm^-1 K^-1 ). Therefore, Si-Ge alloys in the I4₁ /amd space group are potential thermoelectric materials.

Keywords: Si allotrope; ab initio calculations; mechanical properties; semiconductors; thermal conductivity.