We
report the crystal structure and physical properties of a new
actinide-containing equiatomic ternary germanide ThRhGe. This compound
is found to exist in two orthorhombic polymorphs at ambient pressure,
which can be obtained by quenching from different annealing temperatures.
α-ThRhGe crystallizes in the YPdSi-type structure with the Pmmn space group (a = 4.381 6(3)
Å, b = 14.351 8(13) Å, c = 7.506 9(6) Å) and exhibits a normal metallic behavior
down to 1.8 K. In contrast, β-ThRhGe adopts the TiNiSi-type
structure with the Pnma space group (a = 7.298 7(5) Å, b = 4.395 9(3)
Å, c = 7.624 5(5) Å) and shows an
incomplete structural transition into the monoclinic structure (space
group P21/c) at 244 K,
following by a bulk superconducting transition below 3.36 K. The application
of hydrostatic pressure suppresses the structural transition and enhances
superconductivity, whose onset temperature reaches 8.36 K at 2.8 GPa.
The contrasting behavior between the two polymorphs can be explained
qualitatively by theoretical calculations, which show that the Fermi
level lies close to a minimum of density of states in α-ThRhGe
while it is exactly at a van Hove singularity associated with large
density of states in the orthorhombic phase of β-ThRhGe. Our
results suggest that equiatomic ternary intermetallic compounds offer
a new playground for the exploration of interplay among polymorphism,
structural transition and superconductivity.