Physical origin of high performance of thermoelectric clathrates encapstulating off-center guest ions

2016 Fiscal Year Final Research Report

• Project/Area Number: 26400381
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Mathematical physics/Fundamental condensed matter physics
• Research Institution: Hokkaido University
• Principal Investigator: Nakayama Tsuneyoshi 北海道大学, -, 名誉教授 (80002236)
• Co-Investigator(Renkei-kenkyūsha): TAKABATAKE TOSHIRO 広島大学, 大学院・先端物質科学研究科, 名誉教授 (40171540) ; SUEKUNI KOUICHIIRO 九州大学, 大学院・総合理工学研究員エネルギー物質科学部門, 准教授 (10582926)
• Project Period (FY): 2014-04-01 – 2017-03-31
• Keywords: 熱電変換物質 / ガラス / 熱伝導 / クラスレート / 局在現象

Outline of Final Research Achievements

Type-I clathrate compounds exhibit glasslike thermal/dynamic properties depending on on-center or off-center due to symmetry breaking of guest-atom positions in tetrakaidecahedron cages. All of these features are associated with the phonon dynamics in the THz region, for which we have performed large-scale numerical simulations by highlighting the difference between type-I clathrates Ba8Ga16Ge30 (BGG) with on-center guest atoms and Ba8Ga16$Sn30(BGS) with off-center guest atoms. The results of the phonon densities of states D(\omega), the dynamic structure factors S(Q,E), the specific heats C(T), and the participation ratios of eigenmodes have clearly realized a drastic change from the conventional phonon dynamics of BGG to the phonon-glass dynamics of BGS. On the basis of these results, we have given the microscopic mechanism emerging glasslike thermal/dynamics behaviors in type-I clathrate compounds with off-center guest atoms.

Free Research Field

物性物理学