We present the zero-temperature equation of state (pressure dependence of compression) and phase stability predictions for the 5d-transition metals obtained from all-electron density-functional theory (DFT) calculations. The results compare favorably with experiments but extend beyond current experimental capabilities to 10 TPa. Our study reveals phase changes that are explained from the calculated electronic structure. The cubic face-centered and body-centered structures (fcc and bcc), together with two-, three-, and four-layered hexagonal structures, play major roles under compression. The results' dependence on the electron exchange and correlation in the DFT approach is investigated, and it is shown that the impact of the choice, while significant at lower pressures, diminishes in the terapascal regime. We further illustrate that the normal parabolic trends in atomic volume and bulk modulus with atomic number, due to the occupation of bonding and anti-bonding 5d states, break down at TPa pressures, suggesting drastically different chemical bonding at these extreme conditions.
The electrical resistivity of Fe alloys at high pressures is a crucial physical parameter for determining the thermal conductivity of and magnetic dynamo generation in planetary cores. Discrepancies exist in previous studies on the magnitude of resistivity change across the bcc (alpha) to hcp (& varepsilon;) transition at similar to 13 GPa at room temperature. To address this, two methods were applied to measure the electrical resistivity of Fe at ambient temperature as a function of pressure in the range 5-24 GPa with high data density in a 3000-ton multi-anvil press. Our measured resistivity through the alpha-& varepsilon; phase transition shows a relative increase of 0.84-1.5, which aligns with mid- to low estimates from previous studies. A nadir of solid Fe thermal conductivity of 30-55 W/m/K at ambient temperature up to 24 GPa is found by the Wiedemann-Franz Law, with implications for greater heat flux in small terrestrial planetary cores by the Bloch-Gr & uuml;neisen Equation.
Phase relations in the MgSiO3-Al2O3 system were investigated at 40.0 GPa and 1700K, and at 44.0, 55.7 GPa and an estimated temperature of similar to 2300 K using a multi-anvil apparatus combined with in situ X-ray diffraction. At 55.7 GPa and similar to 2300 K, coexisting bridgmanite and corundum did not equilibrate. At 44.4 GPa and similar to 2300 K, bridgmanite contains 19.1 +/- 3.6 mol % of Al2O3, and corundum contains 14.6 +/- 1.6 mol % of MgSiO3. At 40.0 GPa and 1700K, bridgmanite contains 24.4 +/- 2.3 mol % of Al2O3, which is significantly larger than previously determined, and corundum contains 11.0 +/- 1.9 mol % of MgSiO3. We suggest that the increase in Al2O3 solubility in bridgmanite may be related to deviatoric stress, although alternative kinetic or textural explanations cannot be excluded. These results indicate that more detailed studies under stress are required to define element partitioning in minerals at lower mantle conditions.
