High p, T physical property studies of Earth's interior: Thermoelectric power of solid and liquid Fe up to 6.4 GPa

Abstract

High p,T experiments provide indirect access to the deep interior of Earth. High p, T research at the University of Western Ontario using large volume cubic anvil presses has focused on in-situ measurements of physical properties of mantle and core related substances as they relate to Earth's interior physical processes. Thermoelectric power measurements of solid and liquid Fe, using twisted Fe/Pt–10%Rh junctions, have been made at p up to 6.4 GPa. By isolating the sign determining energy derivative of the density of states at the Fermi energy, ∂N(εF)/∂ε, in the expression for the Seebeck coefficient of Fe, these measurements show that ∂N(εF)/∂ε is positive for liquid Fe at p below approximately 4.0 GPa but ∂N(εF)/∂ε is negative for p above 4.0 GPa. The solid phase polymorphism which Fe exhibits in this p region, and its influence on the liquid state, is suggested as the explanation for the short range bcc-like and fcc-like properties of the liquid. This finding corroborates our earlier measurements on the p-dependence of the T-coefficient of electrical resistivity of liquid Fe, which showed a similar discontinuity at the δ(bcc)–γ(fcc)-liquid triple point pressure.