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제124회 대한화학회 학술발표회, 총회 및 기기전시회 안내 Zintl Phase Solid-State Compounds for Energy Material Applications

2019년 8월 29일 16시 37분 54초
INOR1-2 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
목 16시 : 05분
Inorganic Chemistry - Recent Trends in Inorganic Chemistry I: Bioinorganic Chemistry
저자 및
Tae-Soo You
Department of Chemistry, Chungbuk Natioanl University, Korea
The Zintl phase A5M2Pn6 (A = Ca, Sr, Eu, Yb; M = Al, Ga, In; Pn = As, Sb, Bi) series has been extensively investigated by worldwide researchers for thermoelectric applications. Our recent studies for the Ca5-xYbxAl2Sb6 (1.0 ≤ x ≤ 5.0) system, where two cations of Ca and Yb formed a solid-solution mixture, revealed that some Yb-rich compounds with a particular range of composition originally adopted the Ba5Al2Bi6-type phase, but they underwent a structural transformation to the Ca5Ga2As6-type phase during the post-heat-treatment. Moreover, their conductivities were also shifted from metallic to semiconducting during this phase transition. After then, we attempted to apply an anionic p-type dopant Ge in the Ca5-xYbxAl2Sb5-xGey system and successfully enhanced the Seebeck coefficient. In addition, we also proved that originality of the structural transformation was descended from the site-preference of Ca and Yb. To further expand our understanding about the A5M2Pn6 series, we applied the cationic n-type dopants using rare-earth metals (RE) and resulted in producing the quinary Ca5-x-yYbxREyAl2Sb6 (RE = Pr, Nd, Sm, Eu, Gd system. As RE3+ dopants were introduced in the Ca-rich compounds, the Ba5Al2Bi6-type phase initially crystallized, but after the post-heat-treatment, the original phase was successfully transformed into the Ca5Ga2Sb6-type phase. Quite interestingly, along with this structural transition, we also observed the p-type to n-type conversion in the title compounds. To the best of our knowledge, this is the first example that shows the p-type to n-type conversion in the A5M2Pn6 (A = Ca, Sr, Eu, Yb; M = Al, Ga, In; Pn = As, Sb, Bi) series induced by the structural transformation from its original Ba5Al2Bi6-type to the Ca5Ga2As6-type phase. To understand this kind of intriguing p-type to the n-type conversion along with its related TE properties, a series of theoretical DFT calculations using several hypothetical models were also performed, and the resultant DOS, COHP, ELF and band structure were thoroughly analyzed. [References] 1. Nam, G.; Choi, W.; Jo, H.; Ok, K.; Ahn, K. and You, T.-S. Chem. Mater. 2017, 29, 1384-1395. 2. Lim, S.; Nam, G.; Shin, S.; Ahn, K.; Lee, Y. and You, T.-S. Inorg. Chem. 2019, 58, 5827-5836.