Ab initio investigation of pressure-induced structural transitions and electronic evolution of Th₃N₄

ABSTRACT

The crystal structures, lattice dynamics, mechanical, electronic properties, and electron–phonon coupling of ${\mathrm{T}\mathrm{h}}_3{\mathrm{N}}_4$ under environmental conditions and high pressures have been studied by merging first-principles calculations and particle-swarm optimization algorithm. Four structures are identified for ${\mathrm{T}\mathrm{h}}_3{\mathrm{N}}_4$, including the $R\overline{3}m$, $I\overline{4}3d$, $R\overline{3}$, and C2/m phases, in which the $I\overline{4}3d$, $R\overline{3}$, and C2/m phases are newly predicted. Their mechanical properties, including the Poisson's ratio σ, the elastic anisotropy factor $A^U$, and the Pugh's ratio $B/G,$ have been calculated and discussed. The results show that the $R\overline{3}m$, $I\overline{4}3d$, and $R\overline{3}$ phases of ${\mathrm{T}\mathrm{h}}_3{\mathrm{N}}_4$ behave ductile nature, while the C2/m phase behaves brittle nature. Among them, the $I\overline{4}3d$ phase of ${\mathrm{T}\mathrm{h}}_3{\mathrm{N}}_4$ almost exhibits completely anisotropic nature. Besides, our electronic band structure calculations show that the pressure-induced semiconductor-metal transition occurs following the $I\overline{4}3d$ to $R\overline{3}$ phase transition. Further, the electron-phonon coupling of the $R\overline{3}$ phase has been analyzed. The results we obtained are of significance to further understand the physical essence of ${\mathrm{T}\mathrm{h}}_3{\mathrm{N}}_4$ and its practical engineering applications.

KEYWORDS:

• Structure prediction
• phase transitions
• mechanical properties
• electronic properties
• first-principles calculations

Acknowledgments

The Shanghai Supercomputing Center are acknowledged for allocation of computing time.

Disclosure statement

No potential conflict of interest was reported by the author(s).

ORCID

Yongliang Guo http://orcid.org/0000-0002-0477-9045

Additional information

Funding

This work is supported by the National Natural Science Foundation of China (grant number 11975100 and 11904081) and the Basic Research Program of Education Bureau of Henan Province, China (No. 20A140007).