First-principles study of type-I and type-VIII Ba8Ga16Sn30 clathrates

Abstract

We calculated the electronic structures and the thermoelectric properties for type-I and type-VIII Ba 8 Ga 16 Sn 30 ͑BGS͒ clathrates. The band structures show that type-I and type-VIII BGS are indirect semiconductors with band gaps of 0.51 eV and 0.32 eV, respectively. The calculated Seebeck coefficient of n-type type-I BGS is higher than that of n-type type-VIII BGS because of the larger density of states in type-I at the bottom of the conduction band. This is in good agreement with the experimental results. We also calculated the electrical conductivity and thermal conductivity due to charge carriers. Estimated thermoelectric figure of merit, ZT, exceeds 1.0 for both types.

Electronic Structures and Thermoelectric Properties of Sb-Doped Type-VIII Clathrate Ba₈Ga₁₆Sn₃₀

“…The relaxation time of BGS-VIII obtained in the present study is three times longer than the previously calculated value (¸= 5.40 © 10 ¹17 s). 23) We believe that this difference is due to some difference in the crystallization process of the samples. Figure 8 shows the calculated thermal conductivity ¬ = ¬ e + ¬ l (¬ e : electronic thermal conductivity, ¬ l : lattice thermal conductivity) of p-type BGSS-VIII with a carrier concentration of n = 5.6 © 10 25 m…”

“…In this study, we calculated the BS and the DOS of BGSS-VIII assuming that the 8c sites are partly occupied by Sb and compared them with those of BGS-VIII. 23) The BS and DOS calculations were performed using the full potential linearized augmented plane wave (FLAPW) method based on the density-functional theory.…”

Effects of Transition Metal (TM: Co, Rh, Ni and Pd) Substitution for Ru on Thermoelectric Properties for Intermetallic Compound RuGa₂

“…To obtain a large S 1113) These compounds form a narrow bandgap of a few hundred meV near E F , comparable to clathrates 14) and skutterudites. 15) The maximum ZT found among these intermetallic compounds is 0.50 at 773 K for RuGa 2 compound. 7) Although the effects of hole 8) and electron doping 10) on the thermoelectric properties above room temperature have been investigated for RuGa 2 , we have investigated various kinds of electron dopants effects on the electrical conductivity and Seebeck coefficient for RuGa 2 compound: we selected single electron doping elements (Co and Rh) and double electron doping elements (Ni and Pd).…”

Optical conductivity spectra of rattling phonons and charge carriers in the type-VIII clathrate Ba8Ga16Sn30Iwamoto1, Mori2, Kajitani3 et al. 2013Phys. Rev. B7050View full textAdd to dashboardCite

“…Thus, carrier dependence in the peak frequencies may also be caused by the electronic structure where the Ba atomic orbitals hybridize with those of Ga and Sn in the conduction band. 27 Electrons on Ba 2+ ions can vary the effective charge of Ba 2+ and hence modify the potential in the atomic cage. The frequency and/or anharmonic potential may be renormalized by such an interaction with n-type carriers, resulting in the carrier dependence ofb and ω 0 .…”