Slicing Diamond—A Guide to Deriving sp³‐Si Allotropes

Abstract

Silicon is the most important material for solar cells. However, its low conversion rate/quantum efficiency requires a rather high material consumption. Thus, researchers undertake enormous experimental and theoretical efforts to find alternative Si allotropes with a better efficiency and in the ideal case a direct electronic band gap. In recent years and months many new allotropic Si structures have been reported; however, they are often described incoherently and without context to existing structures. Our approach allows a classification of many of these allotropes and a relation of their structures to substructures of, for example, known Zintl phases. For this so-called "chemi-inspired" search for promising Si structures we present a "construction kit" as a guide to introducing a large number of tetrahedral Si allotropes, all derived by a modification of the pristine cubic diamond structure. In addition, this approach allows us to realize structural (topological) relationships between experimentally accessible Zintl phases of different composition, such as open tetrahedral frameworks, to a yet unknown extent, including even known phase transitions of specific Zintl phases. In topological, structural, and computational analyses (on a DFT-PBE0/SVP level of theory) we show the close relationship of ten low-energy Si structures derived from the cubic diamond modification; five of them are new, and some show quasi-direct band gaps. A simple deviation of this approach enables the construction of many more tetrahedral structures.

Slicing Diamond for More sp3 Group 14 Allotropes Ranging from Direct Bandgaps to Poor Metals

“…All structures were modeled following the procedure described in the construction part of the recent publication of Jantke et al . The resulting structures were first optimized by using the CRYSTAL09 program package with the Perdew–Burke–Ernzerhof (PBE) DFT functional for the exchange and correlation parts and a modified split‐valence + polarization basis set for Si, Ge, and Sn .…”

“…Other structures with networks of tetrahedrally interconnected Si atoms that form channels were recently proposed as a chemi‐inspired structure based on the BSi 2 framework of LiBSi 2 . Although the three‐dimensional B/Si substructure, constructed from five, six, and seven‐membered rings and with channels for Li atoms, looks rather complex, it was recently shown that this framework is a polytype that simply derives from the diamond structure …”

Predicted Siliconoids by Bridging Si9 Clusters through sp3-Si Linkers

“…In contrast, for [Si(Si 9 12− cluster unit, which is attached to three Au + ions ([Au3Ge45] 9-) had been isolated and structurally characterized [57]. The distances for all four Si-Si bonds at the central Si atom are 2.39 Å.…”

“…Computationally, many novel well-ordered Si allotropes of various dimensionality have been proposed [9,10], but only a few of those were experimentally verified, such as the low-density Si allotropes [11] with clathrate-type structures [12][13][14][15][16][17][18][19]. The focus of the research lies on the description, understanding, and discovery of well-performing photovoltaic materials as well as models for bulk silicon surfaces [20,21].…”

“…Our aim is the computational investigation using substructures or molecular building units that are experimentally known, which we call the chemi-inspired attempt [9,10]. We found that Zintl clusters Further, it was shown that such clusters can serve as seed crystals for the synthesis of Si nanoparticles and nanoscale materials [45,46].…”