[SIT25-P11] Temperature dependency of the electrical grain boundary transport in forsterite aggregates
Keywords:Electrical conductivity, Grain boundary, Grain size dependence
Synthetic samples of forsterite + enstatite (solidus temperature Tm = 1557 C) and forsterite + diopside system (Tm ~ 1350 C) were prepared from the powders of Mg(OH)2 , SiO2 and CaCO3 (≤ 50 nm). Impedance measurements were carried out every 2 ~ 5 minutes during annealing at the highest temperature (1300 ~ 1400 C) for 50 hours and during subsequent gradual cooling down to 1000 C.
Impedance measurements of both forsterite + enstatite and forsterite + diopside during their annealing show grain-size-dependency of their electrical conductivities as s ∝1/d , indicating that the electrical conduction mechanisms are grain boundary transport of the charge carriers in both aggregates. Impedance measurement during the cooling of forsterite + enstatite shows Arrhenius type of temperature dependency of electrical conductivity which changes with temperature ranges such as the dependency well described by activation energy of 240 kJ/mol at 1000 ~ 1150 C, 290 kJ/mol at 1150 ~ 1350 C and 320 kJ/mol at 1350 ~ 1400 C. Forsterite + diopside exhibits stronger temperature dependency than a simple Arrhenius type dependency providing apparent activation energy ranging from 180 kJ/mol to 1000 kJ/mol at temperature from 1000 C to 1350 C (= sample solidus). We will discuss such temperature dependencies based on structural and/or chemical changes of grain boundaries in these systems.