Grain structure–controlled growth of InSb crystals: a grain boundary engineering approach for enhanced thermoelectric performance

Abstract

InSb polycrystalline ingots were prepared using the direct melt quenching method at different cooling rates: slow cooling (SC), air quenching (AQ), and ice water quenching (IWQ). The crystal structure and grain structure of the InSb ingots were analysed by XRD and FESEM. The variations in the grain structure, grain orientation, and grain boundaries of the samples with different cooling rates were analysed by EBSD. The Seebeck coefficient (S) of the InSb samples decreased with increasing cooling rates owing to a slight decrease in the electrical resistivity. A high-power factor (PF) of 6951 µW m⁻¹ K⁻² was achieved for the IWQ sample at 573 K compared to the SC InSb sample (5935 µW m⁻¹ K⁻² at 573 K). The thermal conductivity decreased for the IWQ InSb sample (6.60 W m⁻¹ K⁻¹ at 573 K) compared to SC InSb (7.29 W m⁻¹ K⁻¹ at 573 K) due to the modifications in the grain structures, grain boundary densities and grain boundary characteristics of InSb during rapid cooling, which enhanced the phonon scattering in the IWQ sample. Subsequently, a high zT value of 0.60 was achieved at 573 K for the IWQ InSb sample compared to the SC InSb sample (zT of 0.46 at 573 K).