13C and 11B NMR Spectroscopy of High-Pressure High-Temperature Boron-Doped Diamonds
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-04-01 |
| Journal | Journal of Experimental and Theoretical Physics Letters |
| Authors | Z. N. Volkova, В. П. Филоненко, R. Kh. Bagramov, И. П. Зибров, Nikolai Mikhilovich Shchelkachev |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This study investigates the structural and electronic properties of highly boron-doped diamond (BDD) micropowders synthesized under extreme High-Pressure High-Temperature (HPHT) conditions without metal catalysts.
- Synthesis Achievement: Successfully produced BDD micropowders with high boron concentrations, estimated at 1% (BDD-1) and 2.5% (BDD-2), via direct graphite transformation.
- Lattice Disorder Confirmation: 13C NMR confirmed significant crystal lattice disorder in the BDD samples, evidenced by a large chemical shift (58 ppm) and the presence of substantial sp2-hybridized carbon (graphite-like defects).
- Boron Environment Analysis: 11B NMR spectra were decomposed into four components, identifying the main signal (21-28 ppm) as a superposition of boron atoms in both tetrahedral (BC4) and trigonal (BC3) carbon environments.
- Defect Localization: An additional high-shift 11B signal (63-65 ppm) was observed, strongly suggesting boron localization in highly defective areas, such as dislocation clusters, sub-boundaries, and twin boundaries.
- Structural Correlation: The highest doped sample (BDD-2) showed a shift in the main 11B peak toward lower ppm values (21-22 ppm), indicating that the local BC4 (tetrahedral) environment prevails over BC3 as boron concentration increases.
- Impurity Identification: X-ray diffraction and 11B NMR confirmed the presence of trace impurity phases, including boron carbide (B4C) and cubic boron nitride (cBN), formed during the HPHT process.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Synthesis Method | HPHT Direct Transformation | N/A | Catalyst-free synthesis |
| Boron Concentration (BDD-1) | ~1 | % | Estimated |
| Boron Concentration (BDD-2) | ~2.5 | % | Estimated |
| Lattice Parameter (BDD-1) | 3.5721(3) | A | Increased vs. pure diamond (3.567 A) |
| Lattice Parameter (BDD-2) | 3.5786(3) | A | Highest lattice expansion observed |
| 13C NMR Chemical Shift (BDD-1 Max) | 58 | ppm | Indicates lattice disorder |
| 13C NMR Chemical Shift (sp2 Carbon) | > 100 | ppm | Associated with trigonal carbon defects |
| 11B NMR Shift (Main Component, BDD-1) | 27-28 | ppm | Mixture of BC4 and BC3 environments |
| 11B NMR Shift (Defect Component) | 63-65 | ppm | Boron in highly stressed/defective regions |
| NMR Magnetic Field Strength | 11.74 | T | Bruker AVANCE III spectrometer |
| Plane-Wave Basis Set Cutoff (VASP) | 500 | eV | First-principles calculation parameter |
| BDD-1 Particle Size | Up to 30 | µm | Well-faceted single crystals |
| BDD-2 Particle Size | Up to 20 | µm | Single crystals and intergrowths |
Key Methodologies
Section titled “Key Methodologies”The BDD micropowders were synthesized using a catalyst-free HPHT method, followed by detailed structural analysis using NMR and XRD.
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Precursor Preparation:
- Starting materials included high-temperature pitch, globular nanocarbon, and submicron amorphous boron powder.
- The boron-to-carbon ratio was set at 1:15.
- Mixing was performed in a ball mill using hard-alloy balls in hexane for 1 hour, followed by drying at 50 °C.
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HPHT Synthesis (Toroid Chambers):
- Synthesis utilized toroid-type chambers (0.3 and 2.5 cm3 reaction volume).
- BDD-1 Conditions: Pressure 7.0-7.5 GPa, Temperature 1550 ± 30 °C, Isothermal holding 100 s.
- BDD-2 Conditions: Pressure 7.5-8.0 GPa, Temperature 1750 ± 30 °C, Isothermal holding 5 s.
- The process involved increasing pressure, heating the reaction volume, holding at temperature, and reducing pressure.
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Chemical Purification:
- Resulting diamond powders were chemically purified to remove residual non-diamond carbon and impurities.
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Structural Characterization (XRD and Microscopy):
- X-ray diffraction (Huber Imaging Plate G670) was used for phase composition analysis and lattice parameter calculation (using PIRUM program).
- Electron microscopy (JSM-6390 JEOL) was used to analyze crystal morphology and size.
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Nuclear Magnetic Resonance (NMR) Spectroscopy:
- High-resolution 11B and 13C MAS NMR spectra were obtained at 11.74 T (Bruker AVANCE III).
- MAS frequency was up to 20 kHz.
- Pulse sequence: π/2-t-π-t-echo. Repetition time (TR) varied (e.g., 0.05 s and 10 s for 11B) to analyze components with different spin-lattice relaxation times (T1).
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Computational Modeling:
- First-principles calculations (VASP package) were used to model the energy of boron atoms in graphene clusters, confirming that single boron atoms are energetically favored over boron dimers.
Commercial Applications
Section titled “Commercial Applications”The unique properties of highly boron-doped diamond, particularly its metallic conductivity and structural stability, make it valuable for several high-performance engineering sectors.
- Superconducting Devices: BDD is a p-type superconductor (Tc up to 10 K). These powders are critical for developing superconducting quantum interference devices (SQUIDs) or specialized wiring.
- Advanced Electrodes and Sensors: BDD electrodes exhibit exceptional chemical inertness, wide potential windows, and resistance to fouling, making them ideal for:
- Wastewater treatment (electrochemical oxidation).
- High-sensitivity chemical and biological sensors.
- Harsh environment electrochemistry.
- High-Power Electronics: Diamond’s superior thermal conductivity and wide bandgap, combined with controlled p-type doping, are essential for next-generation high-frequency and high-power electronic devices (e.g., RF transistors, power switches).
- Abrasives and Tooling: As a micropowder, BDD can be used in high-performance abrasive tools, leveraging the enhanced hardness and wear resistance often associated with boron doping.
- Quantum Information Science: While the study focuses on structural defects, the precise control over defect environments (like the highly stressed regions identified by the 63-65 ppm 11B signal) is foundational for engineering specific color centers or spin qubits in diamond.
View Original Abstract
Diamond micropowders with a boron content of 1 and 2.5% that have been synthesized under high pressure and high temperature conditions and studied. The method of nuclear magnetic resonance on 13 C and 11 B nuclei has been used for a comparative analysis of boron-doped diamond and boron-doped graphite. It has been shown that the structure of diamonds with a high boron content is disordered and contains a significant amount of carbon with trigonal coordination. The main signal in the 11 B spectra of diamond microcrystals is due to the sum of contributions from single boron atoms with tetragonal and trigonal carbon environments. An additional signal in the spectra with a chemical shift of more than 60 ppm can be due to boron atoms in the areas of dislocation clusters, sub-boundaries, and other defective areas.