NATURE OF ELECTRICAL CHARGE-CARRIERS IN THE EARTHS LOWER MANTLE FROM LABORATORY MEASUREMENTS

Thermoelectric power measurements on a silicate-perovskite and magnesi owustite assemblage at lower-mantle conditions [(Mg0.89Fe0.11)(2)SiO4 bulk composition at 48 GPa and temperatures up to 2500 K] yield a posi tive Seebeck coefficient, thus implying that the dominant charge carri ers are positive and that electrons in the conduction band (intrinsic carriers) contribute little to the electrical conductivity. The presen t results suggest that electrical transport is likely dominated by ext rinsic charge carriers throughout the entire mantle and, hence, the el ectrical conductivity can be a powerful tool for characterizing minor phases, impurities and defect states of the Earth's deep interior.