A ten-fold coordinated high-pressure structure in hafnium dihydrogen with increasing superconducting transition temperature induced by enhancive pressure

• Published in: Chinese physics B 2023-09, Vol.32 (9), p.97402-525
• Main Authors: Wang, Yan-Qi, Zhang, Chuan-Zhao, Zhang, Jin-Quan, Li, Song, Ju, Meng, Sun, Wei-Guo, Dou, Xi-Long, Jin, Yuan-Yuan
• Format: Article
• Language: English
• Subjects: first principles; phase transition; superconducting transition temperature; transition metal dihydrogen
• ISSN: 1674-1056
• DOI: 10.1088/1674-1056/acc934

High pressure is an effective method to induce structural and electronic changes, creating novel high-pressure structures with excellent physical and chemical properties. Herein, we investigate the structural phase transition of hafnium dihydrogen (HfH 2 ) in a pressure range of 0 GPa–500 GPa through the first-principles calculations and the crystal structure analysis by particle swarm optimization (CALYPSO) code. The high-pressure phase transition sequence of HfH 2 is I 4/ mmm → Cmma → P -3 m 1 and the two phase transition pressure points are 220.21 GPa and 359.18 GPa, respectively. A newly trigonal P -3 m 1 structure with 10-fold coordination first appears as an energy superior structure under high pressure. These three structures are all metallic with the internal ionic bonding of Hf and H atoms. Moreover, the superconducting transition temperature ( T c ) values of Cmma at 300 GPa and P -3 m 1 at 500 GPa are 3.439 K and 19.737 K, respectively. Interestingly, the superconducting transition temperature of the P -3 m 1 structure presents an upward trend with the pressure rising, which can be attributed to the increase of electron–phonon coupling caused by the enhanced Hf-d electronic density of states at Fermi level under high pressure.