Kinetics of Defect-Induced Cation Redistribution in (CoxMg1-x)2SiO4 Olivines

Abstract

Olivines are high-temperature materials in which divalent cations occupy two non-equivalent octahedral sites, M1 and M2. Cation redistribution processes between the M1 and M2 sites are fundamental steps for cation diffusion in olivines. We have performed temperature-jump relaxation experiments on both M1 and M2 sites in (CoxMg1-x)2SiO4 olivines by monitoring the time evolution of optical absorption of Co2+ ions on M1 and M2 sites. Results derived from the modeling of the experimental relaxation curves show that the kinetics of cation exchange is strongly temperature- and composition-dependent and that relaxation times for cation redistribution at about 1000 oC are less than 1 s. The activation energy of cation redistribution is about 2.0 eV.