Wakayama University · Faculty of Systems Engineering

Research keywordsweathered biotite・cesium intercalation・XAFS analysis・thermoelectric materials・first-principles calculations・GaN vacancy defects・atomic layer epitaxy・electron-phonon coupling

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• Structural Modification of Weathered Biotite Induced 6by Cs Intercalation2025 · Yumeno Masebo, Mitsunori Honda, Kosetsu Hayakawa, Masato Oda, Chiaki Iino, Rina Yabuta, Hiroyuki Ishii, Masakazu Muraguchi
• Development of XAFS Analysis to Elucidate the Structural Change of Weathered Biotite under High Temperature2025 · Kosetsu Hayakawa, Masakazu Muraguchi, Yumeno Masebo, Yohichiro Kojima, Masato Oda, Rina Yabuta, Hiroyuki Ishii, Mitsunori Honda
• Sustainable thermoelectric materials: Utilizing Fukushima weathered biotite via molten salt treatment2024 · This study examines the utilization of Fukushima weathered biotite (WB) as an alternative to conventional thermoelectric materials traditionally derived from rare and toxic substances. WB underwent milling, classification, and subsequent heat treatment via molten-salt treatment to produce crystals exhibiting conductivity akin to semiconductors within the 650–850 °C range. Evaluation of WB and the derived crystal’s electrical conductivity and Seebeck coefficient showcased their viability for high-temperature thermoelectric applications. Consequently, WB attained a dimensionless figure of merit (ZT) of 0.015, signaling its potential as a thermoelectric material that surpasses 650 °C.
• Adiabatic Potential for Conformational Change of VGa–VN Complex Defects in GaN2024 · Focusing on a V_Ga–V_N complex vacancy defect in GaN, the adiabatic potential for conformational changes of the V_Ga–V_N is investigated using the density functional theory. There are two types of configurations due to the symmetry of the crystal, it is confirmed that there is almost no difference in their stability or electronic state. Using these configurations as the initial and final states, the defect reaction is analyzed when V_Ga–V_N moves using the climbing‐image nudged elastic band method. The reaction barrier for the migration of V_Ga (V_N) is found to be 2.2 (3.3) eV. It is concluded that these reactions occur frequently as GaN is annealed since the atomic diffusion potential barrier is similar to that in other semiconductors. These results suggest that V_Ga–V_N in GaN moves through the crystal as a pair of vacancies by alternately repeating the V_Ga and the V_N migration. These results provide important knowledge for elucidating the microscopic mechanism of the experimentally observed V_Ga–V_N aggregation reaction.

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