Analysis of the geomagnetic field estimates the electrical conductivity of the Earth's lower mantle to range from 1 to 100 S m-1. However, measurements of the electrical conductivity of (Mg, Fe)SiO3-perovskite and magnesiowustite range from less than 10-3S m-1to as high as 70 S m-1. The presence of water or iron in the lower mantle may account for the observed high conductivity, but alternatively, the perovskite phase may become a fast-ion conductor at lower mantle temperatures and pressures. We have used a constant pressure-constant temperature molecular dynamics simulation to investigate the effect of pressure on fast-ion conductivity in the perovskite KCaF3, a structural analogue of MgSiO3-perovskite. Although increased pressure decreases the ionic conductivity, increasing the pressure also increases the melting point and the high-conductivity regime is extended to a lower fraction of the melting temperature. However, if (Mg, Fe)SiO3-perovskite follows the behaviour of the structural analogue and does become a fast-ion conductor at high temperature, most of the lower mantle may not be hot enough for (Mg, Fe)SiO3-perovskite to be within its fast-ion regime. © 1995.
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