Pressure-Dependent\nPhase Behavior of Chemically Synthesized\nYtterbium Hydride Nanoparticles and Confinement in CMK‑3

In this work, we developed a chemical synthesis protocol\nto prepare\nboth spherical and rod shaped YbH<sub><i>x</i></sub> nanoparticles\nand infiltrate a mesoporous CMK-3 structure with YbH<sub><i>x</i></sub> nanoparticles. The phase evolution of the YbH<sub><i>x</i></sub> nanoparticles was monitored as a function of the\npressure in a diamond anvil cell. The cell volume of the Yb atom showed\nan unexpected positive deviation from the calculated equation of state\n(EoS) for the α-phase (space group <i>Pnma</i>) of\nYbH<sub><i>x</i></sub>. Additionally, the β-phase\n(space group <i>Fm</i>3̅<i>m</i>) YbH<sub><i>x</i></sub> nanoparticles appeared to become amorphous\nat approximately 27 GPa, although the same behavior was not observed\nin the <i>Pnma</i> (α-phase). The <i>Pmna</i> phase remained stable (measured up to 59.3 GPa) and showed a significantly\nhigher than expected volume per Yb atom relative to the calculated\nEoS. This deviation could be attributed to the nanoscale effect on\nthe thermodynamics of ytterbium hydride formation, which could provide\na path forward to accessing higher order ytterbium hydrides (YbH<sub><i>x</i></sub>, <i>x</i> > 3) at pressures\nmuch\nlower than in the bulk metal.