Effects of Cs/Sr intercalation on the structure and electrical conductivity of weathered biotite

Hayakawa, Kosetsu; Muraguchi, Masakazu*; Masebo, Yumeno*; Kojima, Yoichiro*; Oda, Masato*; Yabuta, Rina*; Ishii, Hiroyuki*; Honda, Mitsunori   

Weathered biotite (WB), a clay-based layered mineral, becomes thermoelectrically active after molten-salt treatment above 700C. In this study, we investigate how Cs and Sr intercalation influences its local structure and electrical conductivity. WB was treated with molten salts containing CsCl and/or SrCl, and the resulting materials were analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), and four-probe conductivity measurements. XRF verified Cs/Sr incorporation, while XRD confirmed retention of the layered structure. XAFS revealed that, in the Cs/Sr-intercalated sample, the Sr-Si distance shortens by , at elevated temperatures, indicating a closer interaction with the Si-O layer. Electrical conductivity measured from 630860C showed that Cs/Sr-WB exhibits higher conductivity than Sr-WB in the 630780C region. These results suggest that interlayer ion rearrangement enhances conduction pathways, demonstrating the potential of interlayer structural control for designing clay-based thermoelectric materials.