Crystal Structure and Physical Properties of Au₄Al-Type Suboxides in the Ti–Rh–Si–O and Ti–Ir–Si–O Systems

This study reports the successful synthesis and comprehensive characterization of Ti₃RhSiO and Ti₃IrSiO, the earliest identified members of Ti-based Au₄Al-type materials. These compounds crystallize in the cubic space group <i>P</i>2₁3 (No. 198), with refined lattice parameters of 6.75362(2) Å and 6.75524(1) Å, respectively. Oxygen plays a crucial role in stabilizing the cubic phase, as confirmed by synchrotron X-ray diffraction and the absence of this phase in oxygen-free samples. First-principles calculations and resistivity measurements reveal a robust multiband metallic character, with Ti-3d and Rh-4d (or Ir-5d) orbitals contributing significantly at the Fermi level. Specific heat analysis highlights weak anharmonic lattice vibrations, while magnetoresistance measurements demonstrate negligible field sensitivity. These unique structural and electronic properties provide valuable insights into the development of Ti-based Au₄Al-type compounds, opening new avenues for fundamental materials research.