Abstract
Recently reported synthesis of at high pressure has stimulated great interest in exploring this new iron oxide and elucidating its properties. Here, we present a systematic computational study of crystal structure, chemical bonding, and sound velocity of in a wide range of pressure. Our results establish thermodynamic stability of the experimentally observed pyrite phase (P-phase) of at pressures above 74 GPa and unveil two metastable phases in and symmetry at lower pressures. Simulated x-ray diffraction (XRD) spectra of and match well with measured XRD data of the decompression products of P-phase , providing compelling evidence for the presence of these metastable phases. Energetic calculations reveal unusually soft O-O bonds in P-phase stemming from a low-frequency libration mode of octahedra, rendering the O-O bond length highly sensitive to computational and physical environments. Calculated sound-velocity profiles of P-phase are markedly different from those of the and phases, underscoring their distinct seismic signatures. Our findings offer insights for understanding the rich structural, bonding, and elastic behaviors of this newly discovered iron oxide.
- Received 23 May 2018
DOI:https://doi.org/10.1103/PhysRevB.98.054102
©2018 American Physical Society