A New Superhard sp3-Hybridized Carbon Allotrope with Ultrawide Direct Band Gap - Ibca-C64

At a Glance

Metadata	Details
Publication Date	2025-09-15
Journal	Materials
Authors	Xinyu Wang, Qun Wei, Jing Luo, Meiguang Zhang, Bing Wei
Institutions	Baoji University of Arts and Sciences, Xidian University
Analysis	Full AI Review Included

Technical Analysis and Documentation: Ibca-C₆₄ Superhard Carbon Allotrope

Executive Summary

This documentation analyzes the theoretical prediction of Ibca-C₆₄, a novel all-sp³ hybridized carbon allotrope, focusing on its potential applications in superhard tools and deep-ultraviolet (Deep-UV) optoelectronics.

Novel Material Prediction: Ibca-C₆₄ was predicted using first-principles calculations combined with the RG2 structure search method, exhibiting a previously unknown 44-c net topology.
Exceptional Hardness: The material is classified as superhard, with a calculated Vickers hardness (H_v) of 83.9 GPa, making it highly competitive for extreme hardness applications and cutting tools.
Wide Direct Band Gap: Ibca-C₆₄ possesses a wide direct band gap of 5.58 eV. This is a critical advantage over most existing sp³ superhard carbons, which typically have indirect band gaps, limiting their efficiency in optoelectronic devices.
Deep-UV Potential: The combination of superhardness and a wide direct band gap makes Ibca-C₆₄ an ideal candidate for next-generation wear-resistant electronic devices designed to operate efficiently in the Deep-UV region.
Synthesis Feasibility: The low relative energy (0.295 eV/atom above diamond) and high density (3.465 g/cm³) suggest favorable thermodynamic metastability and a high likelihood of successful synthesis via appropriate high-pressure or plasma-based routes (e.g., MPCVD).
Structural Stability: Confirmed mechanical and dynamical stability through satisfaction of Born stability criteria and positive phonon frequencies across the Brillouin zone.

Technical Specifications

The following hard data points were extracted from the first-principles calculations of the Ibca-C₆₄ structure:

Parameter	Value	Unit	Context
Crystal System	Orthorhombic	N/A	Predicted Ibca-C₆₄ structure
Lattice Parameter (a)	4.525	Å	Unit cell dimension
Lattice Parameter (b)	8.667	Å	Unit cell dimension
Lattice Parameter (c)	9.394	Å	Unit cell dimension
Calculated Density (ρ)	3.465	g/cm³	Extremely high density, only 0.08 g/cm³ below diamond
Relative Energy (ΔE)	0.295	eV/atom	Energy difference above diamond (suggests high synthesizability)
Vickers Hardness (H_v)	83.9	GPa	Superhard classification (comparable to T20 carbon, 83.5 GPa)
Bulk Modulus (B)	409	GPa	Resistance to compression
Shear Modulus (G)	473	GPa	Resistance to shear
Band Gap Type	Direct	N/A	Overcomes limitations of indirect gap superhard carbons
Band Gap Value (E_g)	5.58	eV	Wide band gap semiconductor (Deep-UV applications)
Minimum Shear Strength	42.1	GPa	Dominant failure mechanism under stress

Key Methodologies

The theoretical prediction and characterization of Ibca-C₆₄ relied on advanced computational techniques within the framework of Density Functional Theory (DFT):

Structure Search: The novel structure was predicted using the RG2 method (Space Group and Graph Theory) to constrain the search to orthorhombic crystals exhibiting sp³ hybridization with 64 atoms per unit cell.
Structural Optimization: Calculations were performed using the Vienna Ab initio Simulation Package (VASP 5.4.4) employing the Projector Augmented Wave (PAW) method.
Exchange-Correlation Functional: The Perdew-Burke-Ernzerhof (PBE) functional under the Generalized Gradient Approximation (GGA) was used for structural optimization and property calculations.
Convergence Parameters: A high cutoff energy of 900 eV was used for plane-wave expansion, ensuring high accuracy. Total energy convergence was set to 1 x 10^-5 eV/atom.
Electronic Structure Calculation: The electronic band structure and the critical wide direct band gap were calculated using the more accurate Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional.
Dynamical Stability Confirmation: Phonon spectra were calculated using the PHONOPY package (version 2.9.0) on a 2 x 1 x 1 supercell (128 atoms) to confirm the absence of imaginary modes.

6CCVD Solutions & Capabilities

The research on Ibca-C₆₄ highlights the critical demand for materials that combine extreme mechanical performance with superior electronic properties, particularly for Deep-UV applications. 6CCVD, as a leader in MPCVD diamond synthesis, is uniquely positioned to support the experimental realization and application development of such materials.

Applicable Materials for Replication and Extension

While Ibca-C₆₄ is theoretical, 6CCVD provides commercial diamond materials that serve as the industry standard for the target applications (Deep-UV optoelectronics and superhard tooling):

Optical Grade Single Crystal Diamond (SCD):
- Relevance: SCD is the closest commercial analog, offering the highest achievable hardness (H_v ≈ 93.9 GPa) and a wide band gap (≈5.5 eV).
- Application: Ideal for high-performance cutting edges, high-power optics, and wear-resistant windows where maximum mechanical integrity is required.
High-Purity Polycrystalline Diamond (PCD):
- Relevance: Provides excellent mechanical properties and is scalable to large areas.
- Application: Suitable for large-area abrasive tools and wear-resistant electronic substrates, especially where the required dimensions exceed current SCD growth limits.
Boron-Doped Diamond (BDD):
- Relevance: BDD is a wide band gap semiconductor that can be tuned from insulating to metallic. It is crucial for Deep-UV electrochemical and electronic devices.
- Application: Essential for developing the Deep-UV electronic devices mentioned in the paper, serving as robust, wear-resistant electrodes or active semiconductor layers.

Customization Potential for Advanced Research

6CCVD’s in-house manufacturing capabilities are perfectly aligned to meet the stringent requirements of synthesizing and testing novel superhard carbon phases like Ibca-C₆₄, or developing devices based on its properties:

Requirement from Research	6CCVD Capability	Specification
Synthesis Route	MPCVD Growth	6CCVD utilizes advanced Microwave Plasma CVD, the preferred method for synthesizing high-purity, sp³-hybridized diamond materials.
Large Area Substrates	Custom Dimensions	We offer PCD plates/wafers up to 125mm in diameter, enabling scalable Deep-UV device fabrication and large-format tooling.
Precise Thickness Control	SCD/PCD Layering	Thickness control from 0.1µm (for thin-film devices) up to 500µm (for bulk mechanical components) and substrates up to 10mm.
Surface Finish	Ultra-Low Roughness Polishing	SCD polishing to Ra < 1nm and inch-size PCD polishing to Ra < 5nm, critical for high-quality optical and electronic interfaces.
Device Integration	Custom Metalization	We provide internal metalization services (e.g., Au, Pt, Pd, Ti, W, Cu) necessary for creating ohmic contacts and interconnects on diamond devices, supporting the development of wear-resistant electronics.

Engineering Support

The prediction of Ibca-C₆₄ provides specific targets for future experimental synthesis. 6CCVD’s in-house PhD-level engineering team specializes in optimizing MPCVD parameters (temperature, pressure, gas flow ratios) to achieve specific material properties.

We offer consultation services to researchers aiming to:

Replicate Metastable Phases: Assist in designing MPCVD recipes to explore the synthesis of metastable superhard phases like Ibca-C₆₄, leveraging our expertise in high-pressure and high-temperature diamond growth.
Optimize Deep-UV Performance: Select and customize BDD or high-purity SCD materials for maximum efficiency in Deep-UV optoelectronic and wear-resistant electronic devices.
Mechanical Tooling Design: Provide material selection and custom fabrication for high-performance cutting and abrasive tools requiring extreme hardness and thermal stability.

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

View Original Abstract

A novel all-sp3-hybridized superhard carbon allotrope, Ibca-C64, is proposed based on first-principles calculations combined with the RG2 (space group and graph theory) structure search method. A systematic investigation of its stability, mechanical properties, and electronic structure is performed. The results indicate that the energy difference between Ibca-C64 and diamond is only 0.295 eV/atom, suggesting its metastability. Detailed analysis of its elastic constants and phonon spectrum confirms both mechanical and dynamical stability. The Ibca-C64 structure demonstrates exceptional mechanical performance, with a Vickers hardness of 83.9 GPa. Furthermore, it possesses a wide direct band gap of 5.58 eV, indicating that Ibca-C64 is a superhard semiconductor material with outstanding mechanical properties.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma18184316

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