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

The effects of intrinsic and substitutional point defects M-X (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 M-X is usually more difficult to form than NMX. The vacancies and M-X 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 M-C are twice as those with NMSi and M-Si. The bulk modulus B and Poisson's ratio nu 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 C-12-C-44. The defects only slightly change the phonon free energy F-vib, vibrational entropy S-vib, constant heat capacity C-V, Gibbs free energy G and isobaric heat capacity C-P, whereas they have a great influence on the coefficient of thermal expansion alpha(T) of 3C-SiC. With the increase of external pressure, the G and C-P of all defective compounds increases and decreases linearly, respectively, while the alpha(T) presents multiplex variation characteristic. (C) 2022 The Authors. Published by Elsevier B.V.