Stability and superconductivity of lanthanum and yttrium decahydrides

Abstract

Rare-earth hydrides can exhibit high-temperature superconductivity under high pressure. Here, we apply a crystal structure prediction method to the current record-holding $T_c$ material, LaH${}_{10}$, and a candidate for even higher $T_c$, YH${}_{10}$. We find a pressure-induced phase transition from the experimentally observed cubic LaH${}_{10}$ phase to a new hexagonal phase at around 420 GPa. This hexagonal phase could explain experimental observations of hcp impurities in fcc samples. We find that YH${}_{10}$ forms similar structures to LaH${}_{10}$ and discuss the sensitivity of superconductivity calculations to the computational parameters used.