Abstract
The compression behavior and high-pressure strength of alpha silicon nitride (α-Si3N4) at pressures of up to 60 GPa are studied using synchrotron radiation powder diffraction, complemented with first-principles calculations. Compression experiments reveal that a-Si3N4 remains stable under the highest pressure and ambient temperature and has a bulk modulus of K0 = 256.3(±4) GPa, with a pressure derivative of K′0 = 5.6. However, the bulk modulus of experiment is higher than that of calculation (232.5 GPa). The correlation between strength and pressure is confirmed by diffraction peak broadening data. A transition from elastic deformation to plastic deformation of α-Si3N4 at 20 GPa is observed, indicating that α-Si3N4 begins to yield, with yield strength reaching 21 GPa at pressures of up to 20 GPa. A similar phenomenon is observed for MgO, WB3, and c-BC2N. Additionally, theoretical calculations are basically consistent with diffraction experimental results regarding structural stability and mechanical properties.
Highlights
Silicon nitride (Si3N4) is a very important member of the class of materials known as ultrahigh temperature ceramics (UHTCs)
One Si atom is linked to four N atoms, and the structural units are tetrahedral.2,6 c-Si3N4 [space group Fd3 ̄m (227)], called γ-Si3N4, is stable under high pressure, with a spinel structure,9 where 2/3 of the Si atoms are linked to six N atoms and the remaining 1/3 to four N atoms
The bulk modulus is evaluated through fitting the P–V data with a third-order Birch-Murnaghan equation of state (EOS),23
Summary
Silicon nitride (Si3N4) is a very important member of the class of materials known as ultrahigh temperature ceramics (UHTCs) It has superior physical and chemical properties, including high strength, excellent thermal conductivity, outstanding thermal shock resistance, temperature resistance, and oxidation resistance.. Xu et al. performed first-principles calculations with a quasiharmonic approximation and discovered that α-Si3N4 remained in a metastable phase at high pressure (10 GPa) and temperature (2000 K). The crystal structure and electron density of α-Si3N4 were researched by Toraya and Masatomo et al. through synchrotron radiation powder diffraction experiments. There is a lack of experimental studies on the strength and deformation behavior of α-Si3N4 under high-pressure and ambient-temperature conditions, conditions critical for both the preparation of highperformance Si3N4 ceramics and the evaluation of the potential of applications under extreme conditions. 56 atoms in a 1 × 1 × 2 supercell, as implemented in the Phonopy code. All structures were relaxed and fully optimized until the Hellmann-Feynman force and the total energy were less than 1 × 10−2 eV/Å and 5 × 10−6 eV/atom, respectively
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