[SIT25-P15] Seebeck coefficient measurement of olivine by dual heating system and its application to the redox kinetics of the subducted slabs
Keywords:Seebeck coefficient, redox kinetics, subducted slab, thermal boundary layer, charge carrier, olivine
To determine the Seebeck coefficient under high pressure, we established the cell design with dual heating systems on the 6-axis apparatus. Two disk TiB2 heaters were placed in the octahedral cell to make two insulated heating systems. Temperature differences were produced on the two sides of the sample by dual heaters and the temperatures were measured by separated thermocouples on each side of the sample. In addition, the electromotive force (voltage difference) of the sample was measured by high resolution multimeter. Therefore, we could easily obtain the seebeck coefficient from the formula, S= ΔV/ΔT. To check the reliability of the method, we use two types of P-type silicon single crystals with different boron doping concentrations as the test materials. The results are quite consistent with previous experimental and calculation results obtained at ambient pressure.
In order to better understand the redox kinetics of the subduction zones, olivine, the dominant phase in the upper mantle, is the most important mineral to control the redox condition. We measured the Seebeck coefficient of olivine under high pressure. The Seebeck coefficient of the sintered Fo90 aggregates was measured at 5 GPa. The Seebeck coefficient is positive and decreases with increasing temperature. The positive to negative transition of the charge carrier occurred at around 1100-1200℃. Thus, we can assume that the temperature of the overlying mantle at about 150 km is above 1350℃, and then olivine would behave as N-type semiconductors. In contrast, olivine in the cold slab behaves as P-type semiconductor, suggesting that the cold slab will be oxidized itself by the Seebeck effect.