Abstract
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 GeFP. 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.
Highlights
In the past 20 years, extensive research has been conducted on Mn+1AXn, which is the generic chemical formula of the MAX phases
These materials have attracted much attention since Barsoum and co-workers succeeded to synthesize Ti3SiC2.5 So far, more than 70 MAX phases have been synthesized,[6,7] and the number is still increasing. They possess a hexagonal crystal structure of sheets of metal carbide or nitride octahedra, which is weakly bonded with the interleaved planar closely packed A-group element layers.[8]
The values of equilibrium lattice constants, volume, and formation volume (ΔV, ΔV = V − V0, where V0 is the volume of perfect Mo2GeC) for Mo2GeC with intrinsic defects were calculated
Summary
In the past 20 years, extensive research has been conducted on Mn+1AXn (where n = 1, 2, or 3, M is an early transition metal, A is an A-group element, and X is either C or N1–4), which is the generic chemical formula of the MAX phases These materials have attracted much attention since Barsoum and co-workers succeeded to synthesize Ti3SiC2.5 So far, more than 70 MAX phases have been synthesized,[6,7] and the number is still increasing. They can be used in defense materials, portable electronic devices, medical application, sensors, low-friction surfaces, and aerospace, as well as protective coatings in future nuclear reactors.[1,3,6]
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