Electrical conductivity of hydrous wadsleyite

In situ complex impedance spectroscopy of H (sub 2) O-bearing wadsleyite was performed in a multianvil apparatus at 14 GPa at temperatures up to 950 degrees C in order to determine electrical conductivity. With increasing H (sub 2) O content in wadsleyite the electrical conductivity increases at a rate higher than observed in previous studies. The activation enthalpy in the temperature range studied where proton conduction dominates is low (0.66 eV) suggesting an inevitable crossover to small polaron conduction at moderately higher temperatures, depending on H (sub 2) O concentration. Although the solubility of H (sub 2) O in wadsleyite is significant for a silicate mineral (>3 wt%), the presence of more than trace dissolved H (sub 2) O in wadsleyite is likely to result in a conductivity too high compared to recent estimates of transition-zone conductivity. The use of complex impedance spectroscopy shows that the frequency dependence of electrical properties is very different in the case of H (sub 2) O-bearing silicate phases. At frequencies below 1000 Hz complex impedance spectra contain strong features which likely result from the sample-electrode interface such that including the low-frequency data would lead to artificially low conductivities.