High-Entropy Germanide (RuRhPdPt)_1–<i>x</i>Ir_<i>x</i>Ge: Synthesis, Phase Stability, and Transport Properties

High-entropy compounds (HECs) have attracted interest for their unique properties driven by the so-called "cocktail effect." While HECs have been widely studied, germanium-based high-entropy compounds (HEGs) remain largely unexplored. In this study, we synthesized (RuRhPdPt)_1-<i>_x</i>Ir<i>_x</i>Ge (0.2 ≤ <i>x</i> ≤ 1) and investigated its structural and transport properties. X-ray diffraction confirmed the formation of a single-phase MnP-type (<i>Pnma</i>) structure across the entire composition range, stabilized by entropy-driven effects. The phase transition between single- and multiphase states, controlled by annealing temperature, further supports entropy stabilization. Transport measurements revealed temperature-independent resistivity for <i>x</i> ≤ 0.6, indicating strong electron scattering from extreme chemical disorder. Hall effect measurements for <i>x</i> = 0.2 showed an ultrashort mean free path comparable to atomic spacing. Superconductivity observed in IrGe (<i>x</i> = 1) was systematically suppressed with increasing disorder, suggesting a disorder-induced breakdown of superconducting coherence. This study expands high-entropy materials to germanide systems and highlights the role of anions in tuning electronic and structural properties. Our findings provide insight into entropy-driven phase stabilization and disorder-induced transport phenomena, paving the way for novel high-entropy materials with tunable functionalities.