First-principles study on the high-$T_\text{c}$ superconductivity of Mg-Ti-H ternary hydrides up to the liquid-nitrogen temperature range under high pressures

Pan Min; Wang Yujie; Hu Kaige; Deng Huiqiu

paper

First-principles study on the high- $T_{c}$ superconductivity of Mg-Ti-H ternary hydrides up to the liquid-nitrogen temperature range under high pressures

arXiv:2602.07427

Abstract

Ternary hydrides have emerged as the primary focus of the new wave of research into superconducting hydrides. In this work, Mg-Ti-H ternary hydrides are explored under high pressures up to 300 GPa using the prediction method of the particle swarm optimization algorithm combined with first-principles calculations. Two new structures, $P 4/ nmm$ -MgTiH $_{6}$ and $P mm 2$ -Mg $_{3}$ TiH $_{6}$ , are identified to be thermodynamically stable at both 200 GPa and 300 GPa. Thermodynamically stable structures of Mg $_{3}$ TiH $_{12}$ are also identified, whose space groups are $R 3/ m$ at 200 GPa and $P m 3 ˉ m$ at 300 GPa, respectively. Among these Mg-Ti-H structures, $P 4/ nmm$ -MgTiH $_{6}$ achieves a record-high $T_{c}$ of 81.9 K at 170 GPa, exceeding the boiling point of liquid nitrogen. Such a high $T_{c}$ is primarily attributed to strong electron-phonon coupling (EPC) driven by low-frequency acoustic phonon modes, with the EPC strength reaching a large value of 1.54. The $T_{c}$ of $P m 3 ˉ m$ -Mg $_{3}$ TiH $_{12}$ is predicted to be 40 K at 300 GPa. Furthermore, element substitution of Zr(Hf) for Ti achieves considerable enhancement of superconducting properties in our predicted hydrogen-rich and high-symmetric crystal structures, i.e., $P 4/ nmm$ -MgTiH $_{6}$ and $P m 3 ˉ m$ -Mg $_{3}$ TiH $_{12}$ . The high pressure required for dynamical stability is lowered to 100 GPa in both $P m 3 ˉ m$ -Mg $_{3}$ ZrH $_{12}$ and $P m 3 ˉ m$ -Mg $_{3}$ HfH $_{12}$ , and to 90 GPa and 120 GPa for $P 4/ nmm$ -MgZrH $_{6}$ and $P 4/ nmm$ -MgHfH $_{6}$ , respectively. Particularly, the electronic structure near the Fermi level is significantly modified in the $P 4/ nmm$ -MgHfH $_{6}$ phase, and pronounced softening of low-frequency acoustic phonon modes occurs. As a result, the EPC strength is enhanced to 1.72, leading to a higher $T_{c}$ of 86 K.

19 pages, 13 figures, 2 tables

First-principles study on the high-Tc​ superconductivity of Mg-Ti-H ternary hydrides up to the liquid-nitrogen temperature range under high pressures

Abstract

First-principles study on the high- $T_{c}$ superconductivity of Mg-Ti-H ternary hydrides up to the liquid-nitrogen temperature range under high pressures