The systematic study on the stability and superconductivity of Y-Mg-H compounds under high pressure

Abstract

Motivated by recent discovery of yttrium-based high-temperature ternary superconducting hydrides (e.g., CaYH${}_{12}$, LaYH${}_{12}$, and ScYH${}_6$), we have employed evolutionary algorithm and first-principles calculations to comprehensively examine the structural stability and superconductivity of the YMgH${}_x$ system at high pressure. The hydrogen content $x$ and the pressure are both important factors in the stability of these candidate structures. We find that the stability of hydrogen-rich materials frequently necessitates higher pressure. For instance, the pressures to stabilize $P4/mmm$-YMgH${}_8$ and $Cmmm$-YMgH${}_{12}$ are both more than 250 GPa. Hydrogen-less materials, such as $I{4}_1/amd$-YMgH${}_2$ and $P{6}_3/mmc$-YMgH${}_3$, can be stable at pressures as low as 100 GPa. In addition, we find a metastable structure for YMgH${}_6$ with the same space group as the $P4/mmm$-YMgH${}_8$. A metastable sodalite-like face-centered cubic (FCC) structure is also found in YMgH${}_{12}$. These four clathrate structures of $P4/mmm$-YMgH${}_6$, $P4/mmm$-YMgH${}_8$, $Cmmm$-YMgH${}_{12}$, and $Fd\bar{3}m$-YMgH${}_{12}$ is made up of H14, H18, H24, and H24 cages, respectively, in which the H-H pair exhibits weak covalent bonding. According to phonon calculations, $P4/mmm$-YMgH${}_6$ and $P4/mmm$-YMgH${}_8$ require a pressure of 300 GPa to maintain dynamic stability, however $Cmmm$-YMgH${}_{12}$ and $Fd\bar{3}m$-YMgH${}_{12}$ can maintain dynamic stability at pressures of 200 GPa and 250 GPa, respectively. Electron-phonon coupling calculations indicate that they might be potential high-temperature superconductors, with superconductivity intimately linked to the H cage structure. The sodalite structure $Fd\bar{3}m$-YMgH${}_{12}$ has a $T_{\mathrm{c}}$ value of 190 K and a strong electron-phonon coupling constant of 2.18.

7 pages, 5 figures, 1 Supplemental Material

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Cited by in corpus (1)

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