Crystallographic Stability and No Evidence of Higher-Order Saddle Points in the HfFe₆Ge₆-type Kagome Metal ScCo₆Ge₆

While kagome RT₆X₆ (R = Li, Mg, Zr, and rare-earth metals; T = 3d transition metals; X = Ge/Sn) compounds are widely studied, Co-based RCo₆X₆ phases remain largely limited to structural reports, with few systematic studies of their physical properties. Here we report Sn-flux-grown single-crystalline ScCo₆Ge₆ and its structural and physical characterization. Single-crystal X-ray diffraction confirms that ScCo₆Ge₆ adopts the HfFe₆Ge₆-type structure rather than the vacancy-driven Y_0.5Co₃Ge₃-type variant. Across the RCo₆Ge₆ series, structural preference correlates with the Shannon ionic radius of R (8-fold coordination), placing ScCo₆Ge₆ within the stability range of the HfFe₆Ge₆-type framework. Magnetization exhibits weak temperature dependence consistent with Pauli-like paramagnetism. The resistivity is well described by a Bloch-Grüneisen form with a Debye temperature exceeding 230 K, consistent with phonon-dominated scattering. Electrical transport also shows a conventional linear Hall response and negligible magnetoresistance, indicative of simple metallic behavior. Electronic structure calculations identify a Ge-derived quadratic saddle point ∼0.35 eV below E_F, with no evidence of higher-order saddle points near the Fermi level. These results highlight that crystallographic stability and physical properties in RCo₆Ge₆ are governed not only by the Co kagome lattice but also sensitively by the Ge sublattice.