Structure and thermoelectric properties of the n-type clathrate Ba₈Cu₅.₁Ge₄₀.₂Sn₀.₇
2015
Xu, Jingtao | Wu, Jiazhen | Shao, Hezhu | Heguri, Satoshi | Tanabe, Yoichi | Liu, Yongfu | Liu, Guo-Qiang | Jiang, Jun | Jiang, Haochuan | Tanigaki, Katsumi
We study type I clathrate Ba₈Cu₅.₁Ge₄₀.₂Sn₀.₇ single crystals (space group Pm3̄n, no. 223, a = 10.7151(3)) grown using a Sn flux method. Microprobe analysis and single-crystal X-ray diffraction reveal a small amount of Sn embedded in the Cu/Ge framework, which increases disorder at the guest Ba sites. Ba₈Cu₅.₁Ge₄₀.₂Sn₀.₇ is diamagnetic with a susceptibility of ∼2.8 × 10⁻⁷ emu g⁻¹ and shows metal-like behavior (dρ/dT > 0) with a low charge carrier concentration of 0.5 e⁻ per unit cell at 300 K. The single crystals show a relatively high carrier mobility (μ (300 K) = 11.9 cm² V⁻¹) and very low lattice thermal conductivity (∼0.6 W m⁻¹ K⁻¹). The thermoelectric figure of merit ZT of Ba₈Cu₅.₁Ge₄₀.₂Sn₀.₇ single crystals reaches a maximum value of 0.6 at 773 K, which can be further improved by adjusting the chemical composition.
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