Temperature and pressure dependence of electrical conductivity in synthetic anorthite

• Temperature greatly influences conductivity of anorthite much more than pressure.
• Activation enthalpy linearly increases with increasing pressure.
• Ca2+ in anorthite is proposed to be the dominant charge carriers.
• Ca diffusion coefficient in anorthite was calculated from conductivity data.

Electrical conductivity measurements of synthetic anorthite were carried out as a function of pressure and temperature by a Solartron-1260 Impedance/Gain phase analyzer in a multi-anvil apparatus. The impedance spectroscopy was performed in a frequency range from 10–1 Hz to 106 Hz. The sample was synthesized at 1673 K in a high temperature furnace. Our experimental results show that (1) a dramatic increase in electrical conductivity with increasing temperature and a slightly decrease in conductivity with increasing pressure at constant temperature, however, the effect of pressure on the conductivity is less pronounced than that of temperature; (2) the activation enthalpy linearly increases with increasing pressure (1.86–1.91 eV) reflecting the mobility of Ca2+ decreases as the anorthite framework becomes more compressed; (3) the activation energy at atmospheric pressure and activation volume are 1.83 eV and 2.39 cm3/mol, respectively; (4) According to these Arrhenius parameters, it is proposed that the possible dominant mechanism of the charge transport in anorthite under experimental conditions is the hopping of Ca2+ from one near aluminum oxygen site to another; (4) the diffusion coefficient of calcium was calculated from the present conductivity data using Nernst–Einstein equation, and compared with previous experimental results.