Thermoelectric properties of Fukushima weathered biotite for thermoelectric conversion materials

Honda, Mitsunori   ; Kaneta, Yui ; Hayakawa, Kosetsu*; Muraguchi, Masakazu*; Iino, Chiaki*; Oda, Masato*; Ishii, Hiroyuki*; Goto, Takuya*; Yaita, Tsuyoshi

In this study, thermoelectric properties (electrical conductivity, Seebeck coefficient, and thermal diffusivity) were evaluated (OZMA-1-S1) for polycrystalline minerals obtained by systematically changing the conditions of WB and the molten treatment. The Seebeck coefficient and thermal diffusivity were evaluated on the same sample. Macroscopic and microscopic structures were identified by various X-ray analyses and first-principles calculations. As for the electrical conductivity results of WB, the biotite material is usually known as an electrical insulator at room temperature, but after grinding, classification, molten salt treatment, and sintering, it was found to have electrical conductivity on the order of 1.49 10 (V/K) in the temperature range 650-850C, indicating that it has semiconducting electrical conductivity properties. Seebeck coefficient measurements in the same temperature range showed a high value of -2.010 (V/K). Calculating the dimensionless performance index from the obtained results, =0.29 was obtained. Regarding the thermoelectric property evaluation results for the molten salt treated polycrystalline minerals, higher electrical conductivity properties than WB were obtained for the same temperature range. These results suggest that WB can be used to show useful thermoelectric properties in the high temperature region above 650C.