On the formation of phases and their influence on the thermal stability and thermoelectric properties of nanostructured zinc antimonide

To investigate the thermal reliability of the structure and thermoelectric properties of the zinc antimony compounds, undoped (Zn4Sb3) and doped (Zn4Sb2.95Sn0.05 and Co(0.05)Zn(3.9)5Sb(3)) zinc antimonide samples were processed using the powder metallurgy route. It was observed that the as-prepared undoped sample contains a pure beta-Zn4Sb3 phase, whereas the doped samples consist of Omega-ZnSb as the major phase and beta-Zn4Sb3 as the minor phase. Differential scanning calorimetry analysis confirms the stability of the beta-Zn4Sb3 phase up to 600 K. X-ray diffraction data of the undoped and doped samples show that the nanocrystallinity of the as-prepared samples is retained after one thermal cycle. The thermal bandgap, thermopower and thermal conductivity are not affected by the thermal cycle for the doped samples. A maximum power factor of 0.6 mW m(-1) K-2 was achieved in the Sn-doped sample (Zn4Sb2.95Sn0.05). This is enhanced to 0.72 mW m(-1) K-2 after one thermal cycle at 650 K under Ar atmosphere and slightly decreases after the third thermal cycle. In the case of the Co-doped sample (Co0.05Zn3.95Sb3), the power factor increases from 0.4 mW m(-1) K-2 to 0.7 mW m-1 K-2 after the third thermal cycle. A figure of merit of similar to 0.3 is achieved at 573 K in the Zn4Sb2.95Sn0.05 sample. The results from the nanoindentation experiment show that Young's modulus of the Sn-doped sample (Zn4Sb2.95Sn0.05) after the thermal cycle is enhanced (96 GPa) compared to the as-prepared sample (similar to 76 GPa). These important findings on the thermal stability of the thermoelectric and mechanical properties of Sn-doped samples (Zn4Sb2.95Sn0.05) confirm that Sn-doped zinc antimonide samples can be used as efficient thermoelectric materials for device applications.