Hardness and superconductivity in tetragonal LiB4 and NaB4

Qianyi Wang; Honggang Li; Jiahui Wei; Ting Zhong; Li Zhu; Xinxin Zhang; Hanyu Liu; Shoutao Zhang

doi:10.1063/5.0180248

Hardness and superconductivity in tetragonal LiB4 and NaB4

J Chem Phys. 2023 Dec 21;159(23):234707. doi: 10.1063/5.0180248.

Authors

Qianyi Wang¹, Honggang Li¹, Jiahui Wei¹, Ting Zhong¹, Li Zhu², Xinxin Zhang³, Hanyu Liu⁴, Shoutao Zhang¹

Affiliations

¹ Key Laboratory of UV-Emitting Materials and Technology of Ministry of Education, School of Physics, Northeast Normal University, Changchun 130024, China.
² Department of Physics, Rutgers University, Newark, New Jersey 07102, USA.
³ College of Science, Shenyang University of Chemical Technology, Shenyang 110142, China.
⁴ Key Laboratory of Material Simulation Methods and Software of Ministry of Education and State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China.

PMID: 38126624
DOI: 10.1063/5.0180248

Abstract

Boron-based compounds have triggered substantial attention due to their multifunctional properties, incorporating excellent hardness and superconductivity. While tetragonal metal borides LiB4 and NaB4 with BaAl4-type structure and striking clathrate boron motif have been induced under compression, there is still a lack of deep understanding of their potential properties at ambient pressure. We herein conduct a comprehensive study on I4/mmm-structured LiB4 and NaB4 under ambient pressure via first-principles calculations. Remarkably, both LiB4 and NaB4 are found to possess high Vickers hardness of 39 GPa, which is ascribed to the robust boron framework with strong covalency. Furthermore, their high hardness values together with distinguished stability make them highly potential superhard materials. Meanwhile, electron-phonon coupling analysis reveals that both LiB4 and NaB4 are conventional phonon-mediated superconductors, with critical temperatures of 6 and 8 K at 1 atmosphere pressure (atm), respectively, mainly arising from the coupling of B 2p electronic states and the low-frequency phonon modes associated with Li-, Na-, and B-derived vibrations. This work provides valuable insights into the mechanical and superconducting behaviors of metal borides and will boost further studies of emergent borides with multiple functionalities.