First-principles study of structural phase transition and electronic properties of CaO3 under high pressure

The exploration of the calcium-oxygen system at high pressure is crucial for comprehending material behavior and geodynamic processes within Earth's interior. Although CaO3 is considered a potential mineral in the lower mantle, its structure under high pressure remains unclear. In this study, the experimental structure, atomic substitution structures, and crystal structures predicted using the particle swarm optimization algorithm for CaO3 are initially comprehensively investigated using first-principles calculations in the pressure range of 0-135 GPa. The findings suggest that the Aea2 phase is energetically more favorable than the experimentally observed P -421m phase in the pressure range of 0-16.7 GPa, with the P-421m phase becoming stable between 16.7 and 135 GPa. Additionally, the elastic constants and phonon dispersion curves of the phases for CaO3 demonstrate that both maintain mechanical and dynamical stability in the studied pressure range. Finally, the relative stability of the Aea2 and P-421m structures of CaO3 at zero pressure is analyzed by comparing their bond lengths, density of states, electron localization functions, and Bader charges. The results indicate that the energetic superiority of the Aea2 structure over the P-421m structure for CaO3 at 0 GPa may be due to stronger interactions between atomic orbitals in the shorter bonds, stronger O-O bonding, and higher charge gain and loss.