Improved Bulk Materials with Thermoelectric Figure‐of‐Merit Greater than 1: Tl10–xSnxTe6 and Tl10–xPbxTe6. Issue 14 (26th May 2014) - Guo, Quansheng
Abstract Noting the steadily worsening problem of depleted fossil fuel sources, alternate energy sources have become increasingly important; these include thermoelectrics, which may use waste heat to generate electricity. To be economically viable, the thermoelectric figure‐of‐merit, zT, which is related to the energy conversion efficiency, needs to be in excess of unity (zT > 1). Tl4SnTe3 and Tl4PbTe3 were reported to attain a thermoelectric figure‐of‐merit zTmax = 0.74 and 0.71, respectively, at 673 K. Here, the thermoelectric properties of both materials are presented as a function of x in Tl10–xSnxTe6 and Tl10–xPbxTe6, with x varying between 1.9 and 2.05, culminating in zT values in excess of 1.2. These materials are charge balanced when x = 2, according to (Tl+)8(Sn2+)2(Te2−)6 and (Tl+)8(Pb2+)2(Te2−)6 (or: (Tl+)4Pb2+(Te2−)3). Increasing x causes an increase in valence electrons, and thus a decrease in the dominating p‐type charge carriers. Larger x values occur with a smaller electrical conductivity and a larger Seebeck coefficient. In each case, the lattice thermal conductivity remains under 0.5 W m−1 K−1, resulting in several samples attaining the desired zTmax > 1. The highest values thus far are exhibited by Tl8.05Sn1.95Te6 with zT = 1.26 and Tl8.10Pb1.90Te6 with zT = 1.46 around 685 K.