Saturation of electrical resistivity of solid iron at Earth's core conditions

Metallic Aluminum Suboxides with Ultrahigh Electrical Conductivity at High Pressure

Aluminum, as the most abundant metallic elemental content in the Earth's crust, usually exists in the form of alumina (Al₂O₃). However, the oxidation state of aluminum and the crystal structures of aluminum oxides in the pressure range of planetary interiors are not well established. Here, we predicted two aluminum suboxides (Al₂O, AlO) and two superoxides (Al₄O₇, AlO₃) with uncommon stoichiometries at high pressures using first-principle calculations and crystal structure prediction methods. We find that the P4/nmm Al₂O becomes stable above ~765 GPa and may survive in the deep mantles or cores of giant planets such as Neptune. Interestingly, the Al₂O and AlO are metallic and have electride features, in which some electrons are localized in the interstitials between atoms. We find that Al₂O has an electrical conductivity one order of magnitude higher than that of iron under the same pressure-temperature conditions, which may influence the total conductivity of giant planets. Our findings enrich the high-pressure phase diagram of aluminum oxides and improve our understanding of the interior structure of giant planets.

Anharmonic effects on the dynamics of solid aluminium fromab initiosimulations

Two approaches to simulations of phonon properties of solids beyond the harmonic approximation, the self-consistentab initiolattice dynamics (SCAILD) and decoupled anharmonic mode approximation (DAMA) are critically benchmarked against each other and molecular dynamics simulations using a density-functional-theory description of electronic states, and compared to experimental data for fcc aluminium. The temperature-dependence of phonon dispersion and the phonon density-of-states, heat capacity, and the mean atomic displacement for fcc aluminium are examined with these approaches at ambient pressure. A comparison of results obtained with the harmonic approximation to the ones predicted by SCAILD and DAMA reveal a negligible anharmonic contribution to phonon frequencies, a small, but significant influence on heat capacity, and a strong effect on atomic mean-square displacement. The phase space accessed with SCAILD and DAMA is reduced relative to molecular and harmonic lattice dynamics simulations. In particular the DAMA results are in good agreement with displacement amplitudes determined by the Debye-Waller factor in x-ray diffraction experiments.

Thermal Conductivity and Electrical Resistivity of Solid Iron at Earth's Core Conditions from First Principles

We compute the thermal conductivity and electrical resistivity of solid hcp Fe to pressures and temperatures of Earth's core. We find significant contributions from electron-electron scattering, usually neglected at high temperatures in transition metals. Our calculations show a quasilinear relation between the electrical resistivity and temperature for hcp Fe at extreme high pressures. We obtain thermal and electrical conductivities that are consistent with experiments considering reasonable error. The predicted thermal conductivity is reduced from previous estimates that neglect electron-electron scattering. Our estimated thermal conductivity for the outer core is 77±10  W m^{-1} K^{-1} and is consistent with a geodynamo driven by thermal convection.