Isovalent Bi substitution induced low thermal conductivity and high thermoelectric performance in n-type InSb

In this paper, thermoelectric (TE) properties of n-type InSb1-xBix (x = 0.00, 0.02, 0.05 and 0.10) polycrystalline samples, synthesized by single-step vacuum melting reaction, have been studied in the temperature range of 300-623 K. P-XRD confirms the phase purity and preferred orientation of (220) plane. FE-SEM back-scattered electron (BSE) micrographs reveal surface morphology and phase homogeneity, and elemental mapping with EDS is used to identify the chemical composition. The elemental existence and oxidation state of In3+, Sb3+, and Bi3+ in InSb1-xBix are rechecked through XPS analysis. With Bi substitution, the electrical conductivity of InSb increases, whereas Seebeck coefficient starts decreasing. However, the maximum Seebeck coefficient, S of -241 mu V/K at 423 K, was achieved for the composition of InSb0.98Bi0.02. Interestingly, a huge reduction in lattice thermal conductivity, kappa(lattice) from similar to 17.5 W/mK (InSb) to 13.1 W/mK (InSb0.9Bi0.10) at 300 K is observed due to increased phonon scattering from mass-fluctuation and created point defects. Further, the maximum thermoelectric figure of merit, zT was achieved as similar to 0.56 at 623 K with higher Vickers micro-hardness values of similar to 140 HV for the composition of InSb0.98Bi0.02 which is notably higher than the recently reported InSb based materials.