Prediction of a new potential high-pressure structure of FeSiO${}_3$

Abstract

We predict a new candidate high-temperature high-pressure structure of FeSiO${}_3$ with space-group symmetry Cmmm by applying an evolutionary algorithm within DFT+U that we call post-perovskite II (PPv-II). An exhaustive search found no other competitive candidate structures with ABO${}_3$ composition. We compared the X-ray diffraction (XRD) pattern of FeSiO${}_3$ PPv-II with experimental results of the recently reported H-phase of (Fe,Mg)SiO${}_3$. The intensities and positions of two main X-ray diffraction peaks of PPv-II FeSiO${}_3$ compare well with those of the H-phase. We also calculated the static equation of state, the enthalpy and the bulk modulus of the PPv-II phase and compared it with those of perovskite (Pv) and post-perovskite (PPv) phases of FeSiO${}_3$. According to the static DFT+U computations the PPv-II phase of FeSiO${}_3$ is less stable than Pv and PPv phases under lower mantle pressure conditions at 0 K and has a higher volume. PPv-II may be entropically stabilized, and may be a stable phase in Earth${}^{\prime }$s lower mantle, coexisting with $\alpha$-PbO${}_2$ (Columbite-structured) silica and perovskite, or with magnesiowustite or ferropericlase, depending on bulk composition.

References in corpus (1)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials

Cited by in corpus (1)

• Prediction of a Stable Post-Post-Perovskite Structure from First Principles