High-Pressure Synthesis of a Silicon-Rich Ruthenium Silicide, RuSi₃, with a 9-Coordinated Ru Site and a Si-Si...

Ruthenium silicide (Ru-Si) is a technologically important 4d transition metal silicide, and theoretical calculations suggest the possibility of a new Si-rich phase. The novel ruthenium silicide, RuSi₃, was successfully synthesized under high-pressure and high-temperature (HPHT) conditions of 4-14 GPa and 800-1000 °C. This compound was not theoretically predicted and was discovered experimentally for the first time in this study, making it the most Si-rich ruthenium silicide reported to date. It crystallizes in a monoclinic C2/c structure with a = 13.48423(14) Å, b = 7.54146(4) Å, c = 7.98416(8) Å, and β = 123.5351(6)°. DFT calculations indicate that RuSi₃ becomes enthalpically stable above 1 GPa compared to the starting phase, which is consistent with the experimental results. The dependence of the synthesis conditions and HPHT in situ XRD experiments suggest that increasing the pressure enhances the reactivity and lowers the temperature required for synthesis. RuSi₃ has a semimetallic and pseudogap electronic structure and contains a short Si-Si covalent bond network connecting the Ru-Si polyhedra. Our findings not only suggest the possibility of discovering novel silicon-rich transition metal silicides but also unequivocally demonstrate that high-pressure synthesis is an effective strategy for significantly expanding the structural diversity of this compound class.