First-principles investigation of the intrinsic defect-related properties in Mo2GeC

As one of the MAX phases, Mo2GeC can also be considered as a potential material for use in next generation fission and fusion program reactors. We used first-principles calculations to investigate the formation energies, stable configuration, and interatomic bonding of intrinsic defects (mono-vacancy, self-interstitials, antisites, and Frenkel pairs). For all intrinsic defects, only the value of the formation energy for the C vacancy defect is negative, and the biggest formation energy occurs for Ge-FP. The existence of mono-vacancy shrinks the Mo2GeC structure, while the existence of interstitials, antisites, and Frenkel pair defects expands the Mo2GeC structure. In order to further illustrate the stability of defects, we calculated the DOS and PDOS of defects. We can find that defects have a certain effect on the density of states of Mo2GeC. When mono-vacancy and antisite defects are generated, the DOS at the Fermi level decreased, while the production of self-interstitials and Frenkel defects caused the DOS at the Fermi level to increase. We also found that the C vacancy, Ci1, and Mo-Ge antisite pair caused a small pseudo-gap energy at the Fermi level, indicating that their structure is relatively stable, which is consistent with the result of low formation energy. In addition, a small isolated peak at the point of -13.5 eV for Ci1 appeared, which is attributed to the C-2s orbital. We hope that our results could provide theoretical guidance for future experiments and applications of Mo2GeC.