470 / 2019-03-16 11:19:42

Unraveling structure and bonding evolution of newly discovered iron oxide FeO2

high temperature and high pressure

全体主题 > High Pressure Physics and Materials Science

Recently reported synthesis of FeO2 at high pressure has stimulated great interest in exploring this new iron oxide and elucidating its properties. Here we present a systematic computational study [1] of crystal structure, chemical bonding and sound velocity of FeO2 in a wide range of pressure. Our results establish thermodynamic stability of the experimentally observed pyrite phase (P-phase) of FeO2 at pressures above 74 GPa and unveil two new metastable FeO2 phases in Pbcn and P42/mnm symmetry at lower pressures. Simulated x-ray diffraction (XRD) spectra of Pbcn and P42/mnm FeO2 match well with measured XRD data of the decompression products of P-phase FeO2, providing compelling evidence for the presence of these metastable phases. Energetic calculations reveal unusually soft O-O bonds in P-phase FeO2 stemming from a low-frequency libration mode of FeO2 octahedra, rendering the O-O bond length highly sensitive to computational and physical environments. Calculated sound-velocity profiles of P-phase FeO2 are markedly different from those of the Pbcn and P42/mnm phases, underscoring their distinct seismic signatures. Our findings [1-3] offer insights for understanding the rich structural, bonding, and elastic behaviors of this newly discovered iron oxide.