THE EFFECT OF ALUMINA ON THE ELECTRICAL-CONDUCTIVITY OF SILICATE PEROVSKITE

Measurements of the electrical conductivity of silicate perovskite at 25 gigapascals and 1400 degrees to 1600 degrees C show that the conduc tivity of (Mg,Fe)SiO3 perovskite containing 2.89 weight percent Al2O3 is about 3.5 times greater than that of aluminum-free (Mg0.915Fe0.085) SiO3 perovskite. The conduction mechanism in perovskite between 1400 d egrees and 1600 degrees C is most Likely by polarons, because Mossbaue r studies show that the aluminum-bearing perovskite has about 3.5 time s the amount of Fe3+ as the aluminum-free sample. A conductivity-depth profile from 660 to 2900 kilometers based on aluminum-bearing perovsk ite is consistent with geophysical models.