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潜在的超硬材料 ： SiC 2 N 4 和 Si 2 CN 4

潜在的超硬材料 ： SiC 2 N 4 和 Si 2 CN 4. 报 告 人：王洪波 导 师：马琰铭 教授. 吉林大学超硬材料国家重点实验室. Contents. Introduction Computational details Results and discussion Conclusion. I . Introduction.

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潜在的超硬材料 ： SiC 2 N 4 和 Si 2 CN 4

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  1. 潜在的超硬材料：SiC2N4和Si2CN4 报 告 人：王洪波 导 师：马琰铭 教授 吉林大学超硬材料国家重点实验室

  2. Contents • Introduction • Computational details • Results and discussion • Conclusion

  3. I. Introduction • 1. To discover the superhard phases of materials is a long-standing problem of great practical and fundamental importance. • 2. The β-Si3N4 (P63/m ) is the prototype material leading to the postulate that β-C3N4 may be harder than diamond. • 3. The possible incorporation of C into the Si3N4 material is expected to considerably enhance the potential as a superhard material.

  4. Si atom N atom C atom The structure of SiC2N4 and Si2CN4 SiC2N4 Cubic (Pn3m) Si2CN4 Orthorhombic (Aba2) Ralf Rildel et al. Angew. Chem. Int. Ed. Engl. 36. 603 (1997)

  5. Methods and successful applications • Ab initio evolutionary methodology [JCP; 124; 244704] • Several successful applications: Nature 2 篇， 458, 182 (2009) (Yanming Ma，The first author) 457, 863 (2009) PRL 4 篇，101, 107002 (2008); 102, 065501 (2009); 102, 087005 (2009); 102,175506 (2009) PRB 4 篇， 76, 064101 (2007); 78, 014102 (2008); 79,144110 (2009) ; 79, 054101 (2009)

  6. II. Computational details • Structural prediction: ab initio evolutionary algorithm using USPEX code. • Exchange-correlation functional: GGA • Structure optimization and electronic properties: VASP code

  7. III. Results and discussion

  8. I. SiC2N4

  9. The predicted structures of SiC2N4 Cmmm (Orthorhombic) C2/m (Monoclinic) 30 GPa 100 GPa

  10. Enthalpy difference H-HP21/m versus pressure of SiC2N4 Cmmm Pn3m C2/m 4 GPa 29 GPa

  11. Phonon dispersion curves of C2/m and Cmmm phase 0 GPa 0 GPa 100 GPa 4 GPa C2/m Cmmm

  12. Bulk modulus B (GPa), shear modulus G (GPa), Young’s modulus E (GPa) of Cmmm calculated from Voigt-Reuss-Hillapproximation. a. V. V. Brazhkin et al. Philos. Mag. A 82. 231 (2002) b. D. M. Teter, MRS Bull. 23. 22 (1998) c. F. X. Zhou et al. PRB 76. 100101 (2007)

  13. DOS of Cmmm phase Both the Si-N bonding and C-N bonding are mainly governed by the strong hybridization between the p-p states.

  14. Conclusion • 1. C2/m and Cmmm phase are the high-pressure phase of SiC2N4. • 2. Cmmm phase has high bulk and shear modulus. • 3. Cmmm phase is a superhard structure.

  15. II. Si2CN4

  16. The predicted structures of Si2CN4 Monoclinic (C2/m) Monoclinic(P21/m) 30G 100 GPa

  17. Enthalpy difference H-HP21/m(β) versus pressure of Si2CN4 The experimental structure (Aba2) will be transformed to P21/m phase at 6.6 GPa, but it will be stable at above 19 GPa.

  18. Phonon dispersion curves of P21/m phase 0 GPa 100 GPa The P21/m structure is dynamically stable.

  19. Bulk modulus B (GPa), shear modulus G (GPa), Young’s modulus E (GPa) of P21/m a. V. V. Brazhkin et al. Philos. Mag. A 82. 231 (2002) b. D. M. Teter, MRS Bull. 23. 22 (1998) c. F. X. Zhou et al. PRB 76. 100101 (2007)

  20. DOS of P21/m phase The Si-N bonding and C-N bonding are mainly governed by the hybridization between the p-p states. In addition, the hybridization between C-p and N-s in the lower valence band also contribute to the bonding.

  21. Conclusion • P21/m phase is the high-pressure phase of Si2CN4. • P21/m phase is a superhard structure.

  22. Thanks for your attention !

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