A MOLECULAR-DYNAMICS SIMULATION OF THE EFFECT OF HIGH-PRESSURE ON FAST-ION CONDUCTION IN A MGSIO3-PEROVSKITE ANALOG - KCAF3

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(-3) S m(-1) to 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.