High-pressure
X-ray diffraction of PdH
x
and PdD
x
demonstrates that these materials
remain in a face-centered cubic (fcc, Fm3̅m) structure to megabar pressures at room temperature. The
volumes indicate stoichiometric compositions under pressure with x = 1 for both materials. No indication of any phase transition
was observed up to the highest pressures reached in the experiments.
A third-order Birch–Murnaghan equation of state used to fit
the pressure–volume data gives V
0 = 10.73 (±0.03) cm3/mol, K
0 = 147 (±11) GPa, and K
0′
= 4.7 (±0.5), whereas a Vinet fit gives V
0 = 10.74 (±0.03) cm3/mol, K
0 = 143 (±11) GPa, and K
0′ = 5.1 (±0.5), for the combined data for both PdH
x
and PdD
x
. The
results are used to obtain the pressure dependence of the effective
volume of H and D atoms in PdH
x
and PdD
x
to megabar pressures for comparison with
other simple hydrides with implications for superconductivity in this
class of materials.