Manganese olivine II: point defect relaxation

摘要: To investigate the point defect chemistry and kinetic properties of manganese olivine Mn2SiO4, relaxation time (τ) characterizing rate re-equilibration electrical conductivity following a change in oxygen fugacity was measured for single crystals oriented conduction along [010] direction. The experiments were carried out at temperatures T = 1173–1473 K fugacities \(\) with MnSiO3 activity controlled unity. value τ, which ranges from 130 to 1463 s, increases decreasing temperature. At 1273 K, τ regime is factor ∼1.8 smaller than that regime. used calculate chemical diffusivity (\(\)). Values lie range 2.2× 10−10 − 2.5×10−9 m2/s. For regime, semi-log plot vs 1/T yields concave downward curve. Based on these results combined those Part I this work structure Mn-olivine, it proposed determined by coupled diffusion vacancies electron holes rate-control process low high temperatures, respectively. Deconvolution curve into two straight-line segments values mobilities diffusivities Mn holes. These results, data, concentrations conjunction published other transition-metal silicate olivines reveal following: mobility Mn-olivine about orders magnitude Fe-olivine somewhat larger (Mg0.9Fe0.1)-olivine. metal three are similar both temperature dependence. majority defects highest lowest Co-olivine crystals, while (Mg0.9Fe0.1)-olivine between. deviation stoichiometry cation sublattice lower corresponding oxide.