Group 8 metallocenes as single-source precursors for the synthesis of light-element-stabilized FCC phases under extreme conditions

Metallocenes are promising single-source precursors for the synthesis of transition-metal carbides and hydrides due to their atomic-scale mixing of metal, carbon, and hydrogen. In this study, we investigated the high-pressure and high-temperature (HP – HT) behavior of group 8 metallocenes, ferrocene [Fe(C₅H₅)₂] and ruthenocene [Ru(C₅H₅)₂], at pressures up to 68 GPa using a laser-heated diamond anvil cell. Optical and Raman spectroscopic observations revealed that both complexes undergo a transition to an opaque state above ~20 GPa, enabling efficient laser coupling. In situ synchrotron X-ray diffraction measurements demonstrated that HP – HT treatment of ferrocene and ruthenocene above 30 GPa yielded the formation of the face-centered cubic phase, which indicates that the decomposition of metallocenes under extreme conditions facilitates the stabilization of exotic, light-element-incorporated metallic phases. Our findings highlight the potential of organometallic precursors in exploring the structural diversity of metal-light element systems under ultrahigh pressures.