The thermoelectric properties of p-Na x Pb1-x Te 0.85Se0.15, which possesses a high thermoelectric figure of merit due to band convergence, have been systematically investigated for increasing Na concentration (x = 0.01, 0.02, 0.03, 0.05, and 0.07) from room temperature to 773 K. For x values up to 0.03, the hole concentration increases with the Na concentration; however, for x ≥ 0.03, excess Na forms separate microstructures with needle- and plate-like shapes. At high concentrations (x = 0.05 and 0.07) both the number and size of these structures increase (over 10 μm). Differential scanning calorimetry identifies a phase change near 660 K in samples with x = 0.05 and 0.07, confirming the formation of microstructures; this phase change leads to a decrease in electrical resistivity. However, these microstructures do not significantly affect thermal transport, probably because they are too large to scatter phonons. The highest thermoelectric figure of merit, zT, value is 1.6, which is obtained at 760 K for x = 0.05, due to the low thermal conductivity and electrical resistivity.
Bibliographical noteFunding Information:
This study has been supported by the National Research Foundation of Korea (NRF) Grant funded by the Korea Government (MEST) No. NRF-2011-028729 and Low Observable Technology Research Center Program of Defense Acquisition Program Administration and Agency for Defense Development.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering
- Materials Chemistry