High-Pressure Synthesis of Silicon-Rich Chromium Silicides: MoSi2-Type CrSi2 and PdGa5-Type CrSi5 with a Si Network

Two novel chromium silicides, MoSi2-type CrSi2 and PdGa5-type CrSi5, were successfully synthesized under high-pressure and high-temperature (HPHT) conditions at 12 GPa and 600 °C. The "missing" MoSi2-type CrSi2, which was theoretically predicted to be a stable phase of chromium disilicide, was experimentally obtained for the first time, and adopted a tetragonal I4/mmm structure with a = 3.09422(2) Å and c = 7.54051(5) Å. The crystal structure of MoSi2-type CrSi2 differs from that of ambient-pressure phase CrSi2-type CrSi2 in the stacking of close-packed layers. HPHT in situ XRD experiments suggest that the stacking transition in CrSi2 involves a diffusion-promoting liquid phase. PdGa5-type CrSi5, crystallizing in the I4/mcm structure with a = 5.99998(8) Å and c = 9.2363(2) Å, represents the most Si-rich compound among the reported transition-metal silicides. Its formation was confirmed by HPHT in situ XRD, and DFT calculations revealed that its enthalpy was lower than those of the other phases under high pressure. The structure contains covalently bonded Si–Si networks forming tunnel-like frameworks, reminiscent of clathrate architectures. These findings suggest the potential of exploring a novel class of silicon-rich transition-metal silicides and demonstrate that high-pressure synthesis is a powerful strategy for expanding the structural diversity of transition-metal silicides.