The Soret diffusion in laser-heated diamond-anvil cell

The relatively large temperature gradient in laser-heated diamond-anvil cell (LHDAC) can cause the solid-state chemical segregation by the effect of Soret diffusion. Here we examined the chemical heterogeneity in (Mg,Fe)(Al,Si)O3 perovskite, (Mg,Fe)O ferropericlase, perovskite + ferropericlase, and natural granite samples after heating at the lower mantle pressure and temperature (P–T) conditions in the LHDAC. The results demonstrate that Fe, Al, and K migrated from the hot region to the cold region in the laser-heated area, whereas Si was enriched in the hot region. The strong heterogeneity was observed for Mg as well, but the migrating direction of Mg was different between perovskite and perovskite + ferropericlase samples. We also found that the segregation occurred to the largest extent when the sample was mixed with metal powder as a laser absorber. In contrast, the heterogeneity was not formed in the same sample coated with metal, which produced more homogeneous temperature distribution. The segregation was very limited when the sample was heated between the NaCl insulation layers without additional laser absorber. Part of the inconsistencies between the previous LHDAC studies may be attributed to the chemical separation in the sample as a result of Soret diffusion induced by a strong temperature gradient.