Stabilization of N6 and N8 anionic units and 2D polynitrogen layers in high-pressure scandium polynitrides
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2024-03-12 |
| Journal | Nature Communications |
| Authors | Andrey Aslandukov, Alena AslandukovŠ°, Dominique Laniel, Saiana Khandarkhaeva, Yuqing Yin |
| Institutions | University of Edinburgh, Linkƶping University |
| Citations | 21 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled āExecutive SummaryāThe research details the high-pressure synthesis and characterization of four novel scandium polynitrides, identifying them as highly promising High-Energy-Density Materials (HEDM).
- Novel Material Synthesis: Four new scandium nitrides (Sc2N6, Sc2N8, ScN5, and Sc4N3) were synthesized via direct reaction of scandium and nitrogen under extreme conditions (78-125 GPa and 2500 K) using laser-heated Diamond Anvil Cells (LH-DAC).
- Unique Anionic Units: The structures revealed the stabilization of previously unknown catenated nitrogen oligomers: isolated N66- and N86- anionic units.
- 2D Polynitrogen Layers: ScN5 features a unique structural motif consisting of corrugated 2D-polynitrogen layers built from fused N12 rings, a rare structure among known polynitrides.
- Superior Energetic Performance: Calculated metrics show that Sc2N6, Sc2N8, and especially ScN5, possess volumetric energy density (VED), detonation velocity (Vd), and detonation pressure (Pd) significantly higher than those of TNT.
- Electronic Properties: Sc2N6 and Sc2N8 exhibit anion-driven metallicity, while ScN5 is characterized as an indirect semiconductor, suggesting diverse functional applications.
- Stability Confirmation: Density Functional Theory (DFT) calculations confirm the dynamical stability of Sc2N6, Sc2N8, and ScN5, with ScN5 remaining thermodynamically stable down to 40 GPa.
Technical Specifications
Section titled āTechnical Specificationsā| Parameter | Value | Unit | Context |
|---|---|---|---|
| Synthesis Pressure Range | 78 to 125 | GPa | Direct reaction of Sc and N2 |
| Synthesis Temperature | 2500 (Ā±300) | K | Laser-heated DAC experiments |
| ScN5 Density (Ļ) | 3.71 | g/cm3 | Calculated at 0 K, ambient pressure |
| ScN5 Volumetric Energy Density (VED) | 14.0 | kJ/cm3 | Calculated HEDM performance |
| ScN5 Detonation Velocity (Vd) | 9.8 | km/s | Calculated HEDM performance (TNT Vd is 6.9 km/s) |
| ScN5 Detonation Pressure (Pd) | 60 | GPa | Calculated HEDM performance (TNT Pd is 19 GPa) |
| Sc2N8 Volumetric Energy Density (VED) | 11.0 | kJ/cm3 | Calculated HEDM performance |
| Sc2N8 Detonation Velocity (Vd) | 8.3 | km/s | Calculated HEDM performance |
| Sc2N8 Detonation Pressure (Pd) | 43 | GPa | Calculated HEDM performance |
| ScN5 Bulk Modulus (K0) | 205 | GPa | Measure of incompressibility (ScN K0 is 207 GPa) |
| Sc2N6 Crystal System | Triclinic | P-1 (#2) | Structure solved at 78 GPa |
| ScN5 Crystal System | Monoclinic | P21/m (#11) | Structure solved at 96 GPa |
| N-N Bond Length Range (ScN5) | 1.349 to 1.434 | Angstrom | Suggests single bonding (sp3 hybridization) |
Key Methodologies
Section titled āKey MethodologiesāThe novel scandium polynitrides were synthesized and characterized using a combination of extreme high-pressure techniques and advanced synchrotron analysis.
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High-Pressure Synthesis (LH-DAC):
- Scandium pieces were loaded into Diamond Anvil Cells (DACs) embedded in molecular nitrogen (N2) gas, loaded at 1300 bars.
- Samples were compressed to target pressures (78-125 GPa).
- Samples were laser-heated up to 2500 K using a double-sided YAG laser system (1064 nm) to initiate the direct chemical reaction between Sc and N2.
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Pressure and Temperature Monitoring:
- Temperature was determined by fitting the sampleās thermal emission spectra to the grey body approximation of Planckās radiation function.
- Pressure was monitored using the Raman signal from the diamond anvils and X-ray diffraction of the Rhenium (Re) gasket edge.
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Structural Characterization (Synchrotron XRD):
- Synchrotron single-crystal X-ray diffraction (XRD) was performed at facilities including ESRF (ID11, ID15b) and APS (13IDD).
- 2D X-ray diffraction maps were collected to pinpoint the location of crystallites suitable for single-crystal data acquisition.
- Crystal structures were solved using intrinsic phasing (ShelXT) and refined using least-squares minimization (ShelXL).
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Computational Validation (DFT):
- First-principles calculations were performed using Density Functional Theory (DFT) via the VASP package.
- Variable-cell structural relaxations were conducted to verify experimental parameters and determine bulk moduli (K0).
- Dynamical stability was confirmed by calculating phonon dispersion relations (PHONOPY).
- Thermodynamic stability was assessed by calculating the static enthalpy convex hull at various pressures.
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HEDM Performance Modeling:
- Gravimetric and volumetric energy densities (GED, VED) were calculated based on decomposition reactions into ScN and N2.
- Detonation velocity (Vd) and detonation pressure (Pd) were estimated using the Kamlet-Jacobs empirical equations.
Commercial Applications
Section titled āCommercial ApplicationsāThe unique structural and energetic properties of these high-pressure scandium polynitrides position them for applications in advanced energetics and specialized electronics.
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Advanced Energetics and Explosives:
- The high volumetric energy density (VED) and superior detonation performance (ScN5: Vd 9.8 km/s, Pd 60 GPa) make these materials highly attractive for use as next-generation, high-performance explosives and propellants, exceeding the capabilities of conventional materials like TNT.
- Potential use in specialized military or industrial applications requiring maximum energy release per unit volume.
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High-Pressure Chemistry and Synthesis:
- The stabilization of novel N66- and N86- anionic units provides new targets for synthetic chemists, potentially leading to the discovery of new classes of nitrogen-rich compounds recoverable at ambient pressure.
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Specialized Electronic Materials:
- Sc2N6 and Sc2N8 exhibit anion-driven metallicity, suggesting potential use in high-pressure or extreme-condition electronic components where unique charge transport mechanisms are required.
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Semiconductor Development:
- ScN5 functions as an indirect semiconductor, offering a pathway for developing novel scandium-based materials with tailored electronic band structures for optoelectronics or high-power devices.
View Original Abstract
Abstract Nitrogen catenation under high pressure leads to the formation of polynitrogen compounds with potentially unique properties. The exploration of the entire spectrum of poly- and oligo-nitrogen moieties is still in its earliest stages. Here, we report on four novel scandium nitrides, Sc 2 N 6 , Sc 2 N 8 , ScN 5, and Sc 4 N 3 , synthesized by direct reaction between yttrium and nitrogen at 78-125 GPa and 2500 K in laser-heated diamond anvil cells. High-pressure synchrotron single-crystal X-ray diffraction reveals that in the crystal structures of the nitrogen-rich Sc 2 N 6 , Sc 2 N 8, and ScN 5 phases nitrogen is catenated forming previously unknown N 6 6 ā and N 8 6 ā units and $${!,}{\infty }{!,}^{2}({{{{{\rm{N}}}}}}{5}^{3-})$$ <mml:math xmlns:mml=āhttp://www.w3.org/1998/Math/MathMLā> <mml:msub> <mml:mrow> <mml:mspace/> </mml:mrow> <mml:mrow> <mml:mi>ā</mml:mi> </mml:mrow> </mml:msub> <mml:msup> <mml:mrow> <mml:mspace/> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>ā</mml:mo> </mml:mrow> </mml:msubsup> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> anionic corrugated 2D-polynitrogen layers consisting of fused N 12 rings. Density functional theory calculations, confirming the dynamical stability of the synthesized compounds, show that Sc 2 N 6 and Sc 2 N 8 possess an anion-driven metallicity, while ScN 5 is an indirect semiconductor. Sc 2 N 6 , Sc 2 N 8 , and ScN 5 solids are promising high-energy-density materials with calculated volumetric energy density, detonation velocity, and detonation pressure higher than those of TNT.