4. Conclusion
In summary, based on the structure of Ti3AlC2, possible structures for layered ordered double-transition metals MAX compound Ti2ZrAlB2 have been searched by ab initio calculations. One Ti3AlB2 and two new Ti2ZrAlB2 structures have been successfully designed. The calculations of formation enthalpy, phonons and elastic constants all confirmed the phase stabilities of them. High B/G ratios indicate that they are all good ductile materials. Study of their mechanical properties show their Poisson ratios are larger than 0.25, which means ionic bonds dominate in these three crystal materials. The electron localization functions have also demonstrated that the ionic Ti-B and Zr-B bonding play a key role in their chemical properties, but metal bonds also exist in the structures. Results of electronic densities of states show that they all have good electrical conductivity, and the conductivity are mainly contributed by Ti-d and B-p electron orbitals for Ti3AlB2, and Ti-d, Zr-d and B-p electron orbitals for two Ti2ZrAlB2. Although the high temperature resistance of these three MAX compounds in present study is not as good as the MAX carbides, they also have not low melting points. In particular, they also have good ductility. The unusual combination of these properties of these compounds makes them promising candidates in the field of engineering application. At the end of present wok, we also explored the factors limiting its heat resistance, it is due to the weak bonding between Al and the M(2)-B-M(1)-C-M(2) (M=Ti or Zr).
Funding Information: Project supported by the Scientific Research Key Project Foundation of Henan Province (Grant No. 222102230081 and 202102210482), the Foundation of LCP (Laboratory of Computational Physics) (Grant No. 6142A05210101) and the Youth Backbone Project of Henan Province (No. 2019GGJS137).
ACKNOWLEDGMENTS: All the computational work is accomplished in Henan Key Laboratory of Magnetoelectronic Information Functional Materials, Zhengzhou University of Light Industry funded by the Laboratory of Computational Physics and Henan Province.
AUTHOR CONTRIBUTIONS: Shiquan Feng: Funding acquisition; writing–original draft. Feng Guo: Formal analysis; software; writing–review and editing. Yongqiang Wang: Formal analysis; funding acquisition. Chaosheng Yuan: Data curation; investigation. Xuerui Cheng: Methodology; visualization. Feng Miao: Formal analysis, supervision.