Experimental study on the electrical conductivity of quartz andesite at high temperature and high pressure: evidence of grain boundary transport

Abstract. In this study, the electrical conductivity of quartz andesite was measured in situ under conditions of 0.5–2.0 GPa and 723–973 K using a YJ-3000t multi-anvil press and a Solartron-1260 Impedance/Gain-Phase Analyzer. Experimental results indicate that grain interior transport controls the higher frequencies (10²–10⁶ Hz), whereas the grain boundary process dominates the lower frequencies (10⁻¹–10² Hz). For a given pressure and temperature range, the relationship between Log σ and T⁻¹ follows the Arrhenius relation. As temperature increased, both the grain boundary and grain interior conductivities of quartz andesite increased; however, with increasing pressure, both the grain boundary and grain interior conductivities of the sample decreased. By the virtue of the dependence of grain boundary conductivity on pressure, the activation enthalpy and the activation volume were calculated to be 0.87–0.92 eV and 0.56 ± 0.52 cm³ mol⁻¹, respectively. The small polaron conduction mechanism for grain interior process and the ion conduction mechanism for grain boundary process are also discussed.