As-Li electrides under high pressure: Superconductivity, plastic, and superionic states

Inorganic electrides are a new class of compounds catering to the interest of scientists due to the multiple usages exhibited by interstitial electrons in the lattice. However, the influence of the shape and distribution of interstitial electrons on physical properties and new forms of physical states is still unknown. In this work, crystal structure search algorithms are employed to explore the possibility of forming unique electrides in the As-Li system, where interstitial electrons behave as one-dimensional (1D) electron chains (1D electride) in the $Pmmm$ phase of $\mathrm{As}{\mathrm{Li}}_7$ and transform into zero-dimensional (0D) electron clusters (0D electride) in the $P6/mmm$ phase at 80 GPa. The $P6/mmm$ phase has relatively high superconductivity at 150 GPa $\left(T_c=38.4\mathrm{K}\right)$ compared to classical electrides, even at moderate pressure with $T_c=16.6\mathrm{K}$. In addition, a Dirac cone in the band has been observed, expanding the sources of Dirac materials. The survival of $\mathrm{As}{\mathrm{Li}}_7$ at room temperature is confirmed by molecular dynamics simulation at 300 K. At 1000 K, the As atoms in the system act like a solid, while a portion of the Li atoms cycle around the As atoms, and another portion of the Li atoms flow freely like a liquid, showing the unusual physical phenomenon of the coexistence of the plastic and superionic states. This suggests that the superionic and plastic states cannot only be found in hydrides but also in the electride. Our results indicate that superconducting electride $\mathrm{As}{\mathrm{Li}}_7$ with superionic and plastic states can exist in Earth's interior.

Figure 1

(a) Convex hull of As-Li compounds at different pressures. (b) High-pressure phase diagram of stable As-Li compounds at 0–150 GPa. (c) ELF of $Pmmm$ phase $\mathrm{As}{\mathrm{Li}}_7$ at 80 GPa (isosurface = 0.85). (d) ELF of $P6/mmm$ phase $\mathrm{As}{\mathrm{Li}}_7$ at 150 GPa (isosurface = 0.85). (e) Bader charge of $\mathrm{As}{\mathrm{Li}}_7$ from 60 to 150 GPa.

Figure 2

(a) The density of states of $Pmmm$ phase $\mathrm{As}{\mathrm{Li}}_7$ at 60 and 80 GPa. (b) Density of states of $P6/mmm$ phase $\mathrm{As}{\mathrm{Li}}_7$ at 80 and 150 GPa. (c) Variation of EPC coefficients, ${\omega }_{\log }$, and $T_c$ with pressure. (d) Electronic structure of the $P6/mmm$ phase at 150 GPa. (e) Phonon dispersion curves, phonon density of states, and Eliashberg spectral functions for the $P6/mmm$ phase at 150 GPa. (f) comparison of superconductivity with classical electrides [41, 42].

Figure 3

(a) RMSD curves of As and Li at different temperatures with $NVT$ condition. (b) RMSD curves of As and Li at 1000 K with $NPT$ condition. (c) Trajectories at 300 K. (d) Trajectories at 1000 K. (e) RDF curves of As-As at different temperatures. (f) RDF curves of As-Li at different temperatures. (g) RDF curves of Li-Li at different temperatures.