Si96 - A New Silicon Allotrope with Interesting Physical Properties

At a Glance

Metadata	Details
Publication Date	2016-04-13
Journal	Materials
Authors	Qingyang Fan, Changchun Chai, Qun Wei, Peikun Zhou, Junqin Zhang
Institutions	Université Paris-Sud, Xidian University
Citations	33
Analysis	Full AI Review Included

Technical Documentation & Analysis: Si$_{96}$ Silicon Allotrope

Executive Summary

This research investigates the structural, mechanical, and electronic properties of a novel silicon allotrope, Si${96}$, using first-principles calculations. The findings suggest Si${96}$ is a promising material for advanced applications, directly contrasting its properties with conventional diamond silicon (diamond Si).

Material Stability: Si$_{96}$ (Pm-3m space group) is predicted to be both mechanically and dynamically stable at ambient pressure, confirmed by elastic constants and phonon spectra.
Electronic Properties: It is characterized as a narrow indirect band gap semiconductor with a calculated band gap of 0.474 eV (HSE06 functional).
Structural Advantage: The material exhibits a low density (1.737 g/cm³) and a porous, void framework with nanotube-like cavities.
Mechanical Contrast: Si$_{96}$ exhibits ductile behavior (B/G = 1.93) and significantly lower elastic anisotropy (A^U = 0.004) compared to diamond Si (A^U = 0.336).
Target Applications: The unique structure and low density make Si$_{96}$ highly attractive for high-capacity Li-battery anode materials, hydrogen storage, and electronic devices operating under extreme conditions.
6CCVD Relevance: While Si$_{96}$ is theoretical, its proposed applications (extreme electronics, high-stability anodes) are areas where MPCVD Diamond (SCD/PCD/BDD) provides the industry-leading, commercially available solution, serving as the ultimate benchmark for Group IV semiconductor performance.

Technical Specifications

The following hard data points were extracted from the ab initio calculations of Si$_{96}$ and compared to diamond Si.

Parameter	Value	Unit	Context
Space Group	Pm-3m	N/A	Cubic symmetry
Lattice Parameter (a)	13.710	Å	Optimized equilibrium
Density (ρ)	1.737	g/cm³	Ambient pressure (Lower than diamond Si: 2.322 g/cm³)
Band Gap (E_g)	0.474	eV	Indirect gap (Calculated via HSE06 hybrid functional)
Hardness (H)	9.6	GPa	Calculated via Lyakhov/Oganov model (Diamond Si: 13.3 GPa)
Bulk Modulus (B)	52	GPa	Calculated elastic modulus
Shear Modulus (G)	27	GPa	Calculated elastic modulus
Ductility Ratio (B/G)	1.93	N/A	Indicates ductile behavior (> 1.75)
Young’s Modulus (E)	69	GPa	Calculated elastic modulus
Universal Anisotropic Index (A^U)	0.004	N/A	Extremely low anisotropy (Diamond Si: 0.336)
Volume Expansion (Li Insertion)	-0.25%	N/A	For one Li atom insertion (Lower than diamond Si: 2.91%)

Key Methodologies

The structural, mechanical, and electronic properties of Si$_{96}$ were determined using advanced first-principles computational methods.

Calculation Framework: All calculations utilized the Generalized Gradient Approximation (GGA) functional in the Perdew, Burke and Ernzerrof (PBE) form, implemented within the Cambridge Sequential Total Energy Package (CASTEP).
Pseudopotentials: Ultra-soft pseudopotentials were employed to describe core-valence interactions, considering the Si 3s²3p² valence electron configuration.
Energy Cutoff and Sampling: A cutoff energy of 300 eV was used, paired with a tested k-point sampling mesh of 4 x 4 x 4.
Geometric Optimization: The Broyden-Fletcher-Goldfarb-Shanno (BFGS) minimization scheme was used, achieving a maximum stress convergence of 0.02 GPa.
Electronic Structure Refinement: The Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional was applied to accurately calculate the electronic band structure and correct the typical DFT underestimation of the band gap.
Dynamic Stability Check: Phonon spectra were calculated using the linear response approach, also known as Density Functional Perturbation Theory (DFPT), to confirm the dynamic stability of Si$_{96}$ (absence of imaginary frequencies).

6CCVD Solutions & Capabilities

The research highlights the need for advanced Group IV materials capable of functioning in extreme environments (high stability, low anisotropy) and high-performance electrochemical systems (Li-battery anodes). 6CCVD specializes in MPCVD diamond, the definitive material solution for these demanding applications, offering superior performance compared to the theoretical Si$_{96}$ allotrope.

Applicable Materials for Research Extension

Research Application Focus	6CCVD Material Recommendation	Rationale and Advantage
Extreme Condition Electronics	Electronic Grade Single Crystal Diamond (SCD)	SCD possesses a 5.5 eV band gap (vs. 0.474 eV for Si$_{96}$), offering unparalleled stability, thermal management, and radiation hardness for high-power and high-frequency devices.
High-Capacity Anodes	Heavy Boron-Doped Polycrystalline Diamond (BDD PCD)	BDD is a highly conductive, chemically inert, and stable carbon allotrope. It is ideal for electrochemical applications, offering superior corrosion resistance and stability compared to silicon-based anodes.
Mechanical/Anisotropy Studies	Optical/Mechanical Grade PCD Wafers	The paper uses diamond Si as the mechanical benchmark. 6CCVD provides high-quality PCD wafers up to 125mm, allowing researchers to test the ultimate limits of hardness and mechanical stability in a Group IV material.

Customization Potential for Device Integration

To transition theoretical material concepts like Si$_{96}$ into functional devices (e.g., thin-film anodes or extreme electronics), precise material engineering is essential. 6CCVD offers comprehensive customization services:

Custom Dimensions: We supply PCD wafers up to 125mm in diameter, suitable for large-scale research or prototyping of anode materials.
Precision Thickness: SCD and PCD films are available from 0.1 µm to 500 µm. Ultra-thin films (0.1 µm) are critical for maximizing capacity and minimizing volume expansion in Li-battery anode research.
Advanced Polishing: For optical or high-contact applications, we achieve surface roughness (Ra) < 1 nm on SCD and < 5 nm on inch-size PCD, ensuring optimal interface quality.
In-House Metalization: We provide custom metal contact deposition (Au, Pt, Pd, Ti, W, Cu) directly onto diamond substrates, facilitating immediate integration into electronic or electrochemical test setups.

Engineering Support

The theoretical prediction of novel allotropes like Si$_{96}$ requires rigorous experimental validation and material selection. 6CCVD’s in-house PhD team specializes in the physics and chemistry of Group IV semiconductors. We can assist researchers in selecting the optimal diamond material (SCD, PCD, or BDD) to replicate or extend the findings of this research, particularly for projects focused on extreme-condition electronics and high-stability electrochemical systems.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The structural mechanical properties and electronic properties of a new silicon allotrope Si96 are investigated at ambient pressure by using a first-principles calculation method with the ultrasoft pseudopotential scheme in the framework of generalized gradient approximation. The elastic constants and phonon calculations reveal that Si96 is mechanically and dynamically stable at ambient pressure. The conduction band minimum and valence band maximum of Si96 are at the R and G point, which indicates that Si96 is an indirect band gap semiconductor. The anisotropic calculations show that Si96 exhibits a smaller anisotropy than diamond Si in terms of Young’s modulus, the percentage of elastic anisotropy for bulk modulus and shear modulus, and the universal anisotropic index AU. Interestingly, most silicon allotropes exhibit brittle behavior, in contrast to the previously proposed ductile behavior. The void framework, low density, and nanotube structure make Si96 quite attractive for applications such as hydrogen storage and electronic devices that work at extreme conditions, and there are potential applications in Li-battery anode materials.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma9040284

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