Metastable C-centered orthorhombic Si₈and Ge₈

Abstract

A theoretical prediction on the structural stabilities, mechanical properties, and electronic properties of the C-centered orthorhombic (Cco) Si(8) and Ge(8) is presented, inspired by a recently proposed carbon allotrope structure, Cco-C(8). Energetically comparable with previously known metastable phases, Cco-Si(8) and Cco-Ge(8) may be obtained by decompressing the high-pressure β-Sn phases, or by compressing the corresponding nanotubes. The calculated bulk moduli of Cco-Si(8) and Cco-Ge(8) are close to those of the diamond phases. Further study of the electronic properties reveals that the band gaps of Cco-Si(8) and Cco-Ge(8) are tunable with variations in lattice parameters.

Pathways to exotic metastable silicon allotropes

“…While none of the structures were found to have formally direct band gaps, many of them displayed quasidirect gaps and displayed improved visible light absorption. Note that the "Cco-Si 8 " structure calculated by Zhai et al 77 during the same time period is the same structure as "Z" silicon and carbon (and also the same as "Cco-C 8 " 78 and (RL)2 79 ). "M" (cbn) and "Z" (sie) silicon were also calculated by Bautistia-Hernandez et al 80 in 2013.…”

Network topology approach to new allotropes of the group 14 elements

“…Another structure proposed, C8, is also binodal [43,44], whereas the "topological stacking" method of different carbon fragments recently proposed, yielded four-nodal nets as potential allotropes [45]. We note that such four nodal nets are rare when combining high symmetry building blocks, and even in molecular chemistry, where deliberate symmetry breaking molecules or even two or more different building blocks are used, they are seldom found [46].…”

“…The network structure has been emphasized in the latter, showing both the six-and five-membered rings (but not the seven-membered rings). The pink atoms and light blue bonds in the cdp net do not appear in the picture of the Si T12 structure.Unauthenticated Download Date | 5/8/18 7:27 AM possible carbon allotrope by these authors is ubiquitous in chemistry, but generally unknown to mathematicians and physicists [42].Another structure proposed, C8, is also binodal [43,44], whereas the "topological stacking" method of different carbon fragments recently proposed, yielded four-nodal nets as potential allotropes [45]. We note that such four nodal nets are rare when combining high symmetry building blocks, and even in molecular chemistry, where deliberate symmetry breaking molecules or even two or more different building blocks are used, they are seldom found [46].…”

First Principles Study of the Properties of a Tetragonal Germanium

“…It has a density of 4.71 g/cm 3 , smaller than the value 5.28 g/cm 3 of cubic diamond-type Ge. In addition, we also computed their energies, which reveal that the energy of T8-Ge is 87 meV/atom higher than the diamond-type Ge and about 31 meV/atom higher than the Cco-Ge8 [21]. To see the dynamical stability of T8-Ge, we computed its phonon dispersion curves and drew it in Fig.…”

“…Most structures of the above allotropes were resolved by relevant experiments and only several were obtained by theoretical prediction [21,22]. Fujimoto et al [23] predicted a tetragonal germanium, which belongs to the space group I4/mmm with eight Ge atoms in the unit cell, but its properties were not well investigated.…”