First-principles investigation of effects of defects on the physical properties of 3C-SiC under high temperatures and pressures

Abstract

The effects of intrinsic and substitutional point defects MX (M = Li, Na, Mg, Al, K, Sc, Tb, Dy, Ho, Er; X = C, Si) and NMX (NM = H, B, N, P, S) on the formation energy, mechanical and thermodynamic properties of 3C-SiC at various temperatures and pressures have been studied based on density functional theory (DFT) with quasi-harmonic approximation (QHA). The results show that the antisite defects are easier to form than the vacancies under various conditions, and MX is usually more difficult to form than NMX. The vacancies and MX defects greatly reduce the Young's modulus E and shear modulus G of 3C-SiC; whereas the antisite and NMX possess little effects. The decrements of E and G of 3C-SiC with NMC and MC are twice as those with NMSi and MSi. The bulk modulus B and Poisson's ratio ν of 3C-SiC are difficult to be varied by defects. These results can be well interpreted by bond characteristics, which is closely related to the Cauchy pressure C12−C44. The defects only slightly change the phonon free energy Fvib, vibrational entropy Svib, constant heat capacity CV, Gibbs free energy G and isobaric heat capacity CP, whereas they have a great influence on the coefficient of thermal expansion αT of 3C-SiC. With the increase of external pressure, the G and CP of all defective compounds increases and decreases linearly, respectively, while the αT presents multiplex variation characteristic.

Keywords

• First-principles calculations
• Points defects
• Mechanical properties
• Quasi-harmonic approximation
• Thermodynamic properties