  Actinide-bearing intermetallics display unusual electronic, magnetic, and
physical properties which arise from the complex behavior of their 5$f$
electron orbitals. Temperature ($T$) effects on actinide intermetallics are
well studied, but high pressure ($P$) properties and phase stabilities are
known for only a handful of compositions. Furthermore, almost no data exist for
simultaneous high $P$ and high $T$. We performed ambient-$T$ diamond anvil cell
X-ray diffraction experiments to study the behavior of the intermetallic
U$_6$Fe upon compression up to 82 GPa. U$_6$Fe remains stable in the tetragonal
$I4/mcm$ structure over this pressure range. We also performed ambient $P$,
low-$T$ diffraction and heat capacity measurements to constrain U$_6$Fe's
thermal behavior. These data were combined with calculations and fitted to a
Mie-Gruneisen/Birch-Murnaghan thermal equation of state with the following
parameter values at ambient $P$: bulk modulus $B_0$ = 124.0 GPa, pressure
derivative $B'_0$ = 5.6, Gruneisen parameter $\Gamma_0$ = 2.028, volume
exponent $q$ = 0.934, Debye temperature $\theta_0$ = 175 K, and unit cell
volume $V_0$ = 554.4 angstrom$^3$. We report $T$-dependent thermal expansion
coefficients and bond lengths of U$_6$Fe, which demonstrate the anisotropic
compressibility and negative thermal expansion of the crystallographic $c$
axis. Additionally, density-functional theory calculations indicate increased
delocalization of U$_6$Fe bonds at high $P$.
