Metastable C-centered orthorhombic Si8 and Ge8.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• A novel carbon allotrope, C-centered orthorhombic carbon (Cco-C(8)), has been recently proposed.
• Exploring analogous structures in silicon and germanium could lead to new metastable materials.
• Understanding the properties of these materials is crucial for potential technological applications.

Purpose of the Study:

• To theoretically predict the structural, mechanical, and electronic properties of C-centered orthorhombic silicon (Cco-Si(8)) and germanium (Cco-Ge(8)).
• To assess the energetic stability of these novel phases compared to known metastable allotropes.
• To investigate the tunability of their electronic band gaps.

Main Methods:

• First-principles density functional theory (DFT) calculations were employed.
• Structural stability was evaluated through energy calculations.
• Mechanical properties were assessed by calculating bulk moduli.
• Electronic properties, including band gaps, were computed.

Main Results:

• The C-centered orthorhombic silicon (Cco-Si(8)) and germanium (Cco-Ge(8)) structures are predicted to be energetically comparable to known metastable phases.
• These phases can potentially be synthesized by decompressing high-pressure β-Sn phases or compressing nanotubes.
• The calculated bulk moduli of Cco-Si(8) and Cco-Ge(8) are similar to those of diamond phases.
• The electronic band gaps of Cco-Si(8) and Cco-Ge(8) were found to be tunable by adjusting lattice parameters.

Conclusions:

• The C-centered orthorhombic (Cco) silicon (Si) and germanium (Ge) structures represent promising new metastable phases.
• Their mechanical properties are comparable to diamond phases, suggesting potential for robust applications.
• The tunable electronic band gaps indicate potential for use in electronic and optoelectronic devices.