Structure and properties of a chiral polymorph of diamond with a crystal lattice of the SA3 type
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-12-01 |
| Journal | Letters on Materials |
| Authors | V. A. Greshnyakov, E. A. Belenkov |
| Institutions | Chelyabinsk State University |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study presents an ab initio investigation into the structure, stability, and electronic properties of SA3, a novel chiral polymorph of diamond, providing critical data for its potential synthesis and application.
- Structural Origin and Stability: The SA3 phase is modeled as being formed by the polymerization of close-packed chiral carbon nanotubes (5,4). Molecular dynamics simulations at 300 K confirm the structure is stable under normal conditions.
- High Cohesive Energy: The cohesive energy of SA3 (0.525 Rydberg/atom) is exceptionally high, only 9% less than that of cubic diamond (3C), suggesting superior mechanical hardness and compressibility.
- Electronic Properties: SA3 behaves as a wide-gap semiconductor. Its minimum direct band gap is calculated to be 19% less than the corresponding value for 3C diamond.
- Crystallography: The structure possesses a hexagonal unit cell with parameters a = 0.40696 nm and c = 0.24779 nm, belonging to the chiral space group P6122 (or P6522).
- Experimental Identification: Unique spectral fingerprints (Powder XRD, Raman, and X-ray Absorption Spectroscopy) are provided, allowing for unambiguous experimental identification of the SA3 phase in synthesized carbon materials.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Crystal System | Hexagonal | N/A | Diamond Polymorph SA3 |
| Space Group | P6122 (or P6522) | N/A | Chiral symmetry |
| Lattice Parameter a | 0.40696 | nm | Unit cell dimension |
| Lattice Parameter c | 0.24779 | nm | Unit cell dimension |
| Carbon Atoms per Cell | 6 | N/A | N/A |
| Cohesive Energy | 0.525 | Rydberg/atom | 91% of 3C diamond cohesive energy |
| Minimum Direct Band Gap | 19% less | N/A | Compared to 3C diamond |
| Shortest Bond Length (L1) | 0.15661 | nm | Interatomic distance |
| Longest Bond Length (L4) | 0.16098 | nm | Interatomic distance |
| Most Intense XRD Peak (d100) | 0.35244 | nm | Powder X-ray Diffraction |
| Raman Wavenumber Range | 660 to 1210 | cm-1 | Contains five distinct peaks |
| XAS Photon Energy Range | 290 to 315 | eV | Core-level C1s absorption |
| Structural Stability | Stable | N/A | Confirmed by MD simulation at 300 K |
Key Methodologies
Section titled âKey MethodologiesâThe structural and electronic properties of the SA3 polymorph were determined using advanced first-principle computational methods:
- Computational Framework: Density Functional Theory (DFT) was employed, implemented using the Quantum ESPRESSO software package.
- Exchange-Correlation Functional: Calculations utilized the Generalized Gradient Approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional.
- Ionic Core Treatment: Norm-conserving Troullier-Martins pseudopotentials were used to account for ion-core effects.
- K-Point Sampling: A 12x12x14 k-point mesh was used for Brillouin zone integration of the primitive hexagonal cell.
- Energy Cutoff: The kinetic energy cutoff for the plane-wave basis set was set at 60 Rydberg.
- Structural Relaxation: Relaxation was performed until the force acting on any atom was less than 15 meV/nm, and internal stress was less than 50 MPa.
- Thermal Stability Check: Molecular Dynamics (MD) modeling was conducted at 300 K using a 24-atom supercell (6x6x8 k-point grid) with a 1 fs time step to confirm structural stability under normal conditions.
- Spectroscopic Simulation:
- Powder X-ray Diffraction (XRD) was calculated assuming a Cu-Kalpha wavelength (0.15405 nm) and a coherence length of 50 nm.
- Raman spectra were calculated using established methodologies for vibrational analysis.
- X-ray Absorption Spectra (XAS) were calculated for a 2x2x3 hexagonal supercell.
Commercial Applications
Section titled âCommercial ApplicationsâThe SA3 polymorph, characterized by high stability, extreme hardness, and wide-gap semiconductor behavior, is suitable for applications requiring materials with superior mechanical and electronic performance.
- High-Power/High-Frequency Electronics: As a wide-gap semiconductor, SA3 could be utilized in devices operating under extreme conditions (high temperature, high voltage) where traditional silicon or even cubic diamond (3C) may be limited.
- Ultra-Hard Coatings and Tools: The high cohesive energy, comparable to diamond, makes SA3 a candidate for manufacturing superhard protective coatings, cutting tools, and abrasive materials.
- Advanced Structural Composites: Its predicted high hardness and compressibility suggest use in structural components requiring exceptional mechanical integrity, potentially surpassing silicon carbide (SiC).
- Deep-UV Optoelectronics: The wide band gap is ideal for developing detectors, emitters, and optical components operating in the ultraviolet spectrum.
- Novel Carbon Allotrope Synthesis: The proposed synthesis routeâstatic compression of close-packed chiral carbon nanotubes (5,4)âprovides a practical pathway for experimentalists seeking to create new diamond-like materials.
View Original Abstract
An ab initio study of a chiral polymorphic type of diamond (SA3), in which all atoms are in crystallographically equivalent states, was carried out. The calculations of the structure and properties were performed using the density functional theory method in the generalized gradient approximation. The crystal structure of the SA3 diamond polymorph can be formed during the polymerization of close-packed chiral carbon nanotubes (5, 4). The SA3 phase has a hexagonal unit cell with parameters a = 0.40696 nm and c = 0.24779 nm, which contains six carbon atoms. The crystal lattice of the SA3 diamond polymorph belongs to the space symmetry group P6122 (P6522). The cohesive energy of the SA3 phase is 0.525 Rydberg / atom, which is only 9 % less than the cohesive energy of cubic diamond. Molecular dynamics modeling showed that the structure of the SA3 phase should be stable under normal conditions. The chiral diamond polymorph can exhibit the properties of a wide-gap semiconductor, since its minimum direct band gap is 19 % less than the corresponding value for diamond. The SA3 diamond polymorph can be unambiguously identified experimentally using diffraction and spectral analysis methods. It is found that the calculated powder X-ray diffraction pattern of this phase is characterized by the five most intense maxima, which correspond to the following interplanar distances: 0.35244, 0.20309, 0.17622, 0.14361, and 0.11740 nm. The X-ray absorption spectrum of the SA3 phase differs significantly from similar spectra of diamond and graphite in the photon energy range from 290 to 315 eV. The calculated Raman spectrum of the chiral phase contains five peaks in the range of wavenumbers from 660 to 1210 cmâ1; therefore, the identification of the SA3 phase should not cause difficulties.