The recent successful
findings of H3S and LaH10 compressed above 150
GPa with a record high Tc (above 200 K)
have shifted the focus on hydrogen-rich materials
for high superconductivity at high pressure. Moreover, some studies
also report that transition-metal ternary hydrides could be synthesized
at a relatively low pressure (∼10 GPa). Therefore, it is highly
desirable to investigate the crystal structures of ternary hydrides
compounds at high pressure since they have been long considered as
promising superconductors and hydrogen-storage materials with a high Tc, and can be possibly synthesized at low pressure
as well. In this work, combining state-of-the-art crystal structure
prediction and first-principles calculations, we have performed extensive
simulations on the crystal structures of YSHn (n = 1–10) compounds from ambient
pressure to 200 GPa. We uncovered three thermodynamically stable compounds
with stoichiometries of YSH, YSH2, and YSH5,
which became energetically stable at ambient pressure, 143, and 87
GPa, respectively. Remarkably, it is found that YSH contains monoatomic
H atoms, while YSH2 and YSH5 contain a mixture
of atomlike and molecular hydrogen units. Upon compression, YSH, YSH2, and YSH5 undergo a transition from a semiconductor
to a metallic phase at pressures of 168, 143, and 232 GPa, respectively.
Unfortunately, electron–phonon coupling calculations reveal
that these compounds possess a weak superconductivity with a relatively
low Tc (below 1 K), which mainly stem
from the low value of density of states occupation at the Fermi level
(EF). These results highlight that the
crystal structures play a critical role in determining the high-temperature
superconductivity.