Reduction in Lattice Thermal Conductivity of InSb by Formation of the ZnIn₁₈GeSb₂₀ Alloy

Abstract

InSb is known to be a good candidate as a thermoelectric (TE) material owing to its high carrier mobility and narrow band gap of around 0.18 eV. However, a high ZT value has not been achieved in InSb because of its high lattice thermal conductivity (κ_lat). In order to reduce the κ_lat of InSb, In³⁺ ions in InSb were partly replaced by Zn²⁺ and Ge⁴⁺ ions to form the ZnIn₁₈GeSb₂₀ alloy. Polycrystalline samples of ZnIn₁₈GeSb₂₀ were prepared by a powder metallurgy process combining mechanical alloying and hot pressing followed by water quenching or slow cooling. The TE properties of the quenched and slow-cooled samples were examined over the temperature range of room temperature to 723 K. The κ_lat values of the quenched and slow-cooled samples at room temperature were 2.70 and 2.83 W m⁻¹ K⁻¹, respectively. These values were approximately 6 times lower than that of InSb, presumably due to grain refinement through MA and effective alloy scattering from the multi-component system. The present study confirmed that the relatively large secondary phase would played an important role for the decreased the thermal conductivity in the Zn–In–Ge–Sb system unlike the AgPb_mSbTe_m+2 (LAST-m) system, in which nano-sized Ag–Sb inclusion are embedded in the PbTe matrix.