Thermoelectric property of compound-added α-Fe2O3

We focused on alpha-Fe₂O₃ at resistant material for thermoelectric power generation system from exhausted heat at high temperature. But, alpha-Fe₂O₃ has high electrical resistivity which was disadvantage to thermoelectric materials. We investigated to decrease electrical resistivity by added compound to alpha-Fe₂O₃. We studied Ta₂O₅ and Li₂CO₃ as adding substance. These were different valencies from Fe³⁺. And ion radius is near to Fe³⁺. We added the compounds at more rate than solid solubility limit. For, the compounds exist at grain boundaries. Therefore, the compounds in grain boundary are supposed to reduce electrical resistivity as well as thermal conductivity. As the results of electrical resistivity, the standard was 1times10^-1 mum near 1000 K. The 10 mol% Ta₂O₅-added sample showed 2times10^-3 Omegam near 1000 K. The electrical resistivity of 10 mol% Ta₂O₅-added sample decreased by 1/50 as compared to the standard. The electrical resistivity of the 10 mol% Li₂CO₃-added sample was 3times10^-3 mum near 1000 K. The thermal conductivity of the standard was 25 W/mK near 300 K and down to 4.4 W/mK near 900 K. On the other hand, thermal conductivity of the 10 mol% Li₂CO₃-added sample decreased down to 2.7 W/mK near 800 K. Dimensionless figure of merit of the standard was 9times10^-4 near 900 K and, increased up to 1times10^-2 at 900 K in the 10 mol% Ta₂O₅-added sample.