  The recent discovery of a class of sodalite-like clathrate superhydrides
(e.g., YH6, YH9, ThH9, ThH10, and LaH10) at extreme pressures, which exhibit
commonly a high-temperature superconductivity with the highest Tc approaching
260 K for LaH10, opened up a new era in search of high-temperature
superconductors in metal superhydrides. There is a high interest towards the
finding of alternative clathrate superhydrides that might witness the
long-dreamed room-temperature superconductivity. Here, we target on the
experimental synthesis of strongly-correlated europium (Eu) superhydrides where
theory can fail for the prediction of superconductivity. We pressurized and
laser-heated the mixture of metal Eu and ammonia borane (NH3BH3) in a diamond
anvil cell and successfully synthesized the sodalite-like clathrate EuH6 and
EuH9 at conditions of 152 GPa and 1,700 K, and 170 GPa and 2,800 K,
respectively. Two non-clathrate structured phases of EuH5 and EuH6 were also
synthesized that are not reported in lanthanide superhydrides. Calculated large
H-derived electronic density of states at the Fermi level in clathrate EuH6
implies the potential of high temperature superconductivity. Our work created a
model superhydride platform for subsequent investigation on how
strongly-correlated effect in electronic structure can affect the
superconductivity of superhydrides, a phenomenon that is not known thus far.
