Theoretical Studies on the Thermo- electric Properties of Tin-based Clathrates:Cs8 M4 Sn42(M=Zn,Cd,Hg) and Cs8Sn44□2

The site occupancies and thermoelectric properties of tin-based clathrates Cs8M4Sn42(M=Zn,Cd,Hg)and Cs8Sn44 2were studied by the first principle calculations.We had provided an efficient way to probe the relationship between the crystalline structure and power factor.Detailed analyses indicated the p states of Sn at 16i and 24k sites together with the p states of M substitute contributed significantly to the maximum power factor,yet Cs atoms nearly did not.The dangling bonds of vacancies in Cs8Sn44 2are also discussed.The power factors of p-and n-type Cs8M4Sn42and Cs8Sn44 2at optimal temperature and carrier concentration are predicted.Our results suggest that Cs8Zn4Sn42is a promising candidate at the 5.25×1019cm–3hole carrier concentration as a high temperature thermoelectric material that is competitive to the state-of-art Ge-based clathrate thermoelectric materials.