Thermoelectric Transport in p -Type (Pb 0.98 Na 0.02 Te) 1− x (Zn 0.85 Al 0.15 Te) x -Te Composites Fabricated Using a Combination of Hydrothermal Synthesis and Evacuating-and-Encapsulating Sintering

Two precursors, viz. Pb 0.98 Na 0.02 Te and Zn 0.85 Al 0.15 Te, have been synthesized using low-temperature hydrothermal synthesis, followed by thorough mixing and grinding to obtain (Pb 0.98 Na 0.02 Te) 1− x (Zn 0.85 Al 0.15 Te) x -Te composites with x = 0.04, 0.08, 0.12, and 0.20. The resulting powders were sintered at 380°C for 24 h in an evacuated and encapsulated ampoule. Electrical and thermal properties of the resulting composites were measured as a function of temperature between 90 K and 300 K. Interestingly, both the electrical conductivity and thermopower increased with increasing x . Considering that the resistivity of Zn 0.85 Al 0.15 Te is higher than that of Pb 0.98 Na 0.02 Te, these experimental results might be associated with short-range percolation or band bending after compositing. The total thermal conductivity at room temperature for the composites with x = 0.04, 0.08, and 0.12 was lower than 1.5 W/m-K, significantly below the range of 2 W/m-K to 3.2 W/m-K for PbTe. The composite with x = 0.08 exhibited the highest zT value of about 0.07 at 300 K.