Thermoelectric materials can be utilized to generate electricity from a temperature gradient, thereby recycling the nowadays abundant waste heat, as well as for cooling applications by creating a temperature gradient from electricity. The former is based on the Seebeck effect, and the latter on the Peltier effect. Noticing the continuously declining fossil fuel resources and mankind's increasing need for energy, the importance for clean thermoelectric energy generation continues to climb.Traditional thermoelectric materials were based on the binary tellurides Bi 2 Te 3 and PbTe, which have been utilized for decades. The focus on tellurium as the heaviest non-radioactive chalcogen stems from the observation that heavier elements are advantageous for a reduced thermal conductivity, which is essential for the thermoelectric energy conversion. Moreover, tellurides are less ionic than sulfides or selenides, which leads to an enhanced carrier mobility that is advantageous for the desired high electrical conductivity. This review presents these traditional routes to low thermal conductivity, as well as alternatives based on the lighter analogues of tellurium, namely sulfur and selenium.

High-performance thermoelectric materials are currently being sought after to recycle waste heat. Copper chalcogenides in general are materials of great interest because of their naturally low thermal conductivity and readily...

The aim of this study was to investigate the thermoelectric properties of hot-pressed Ba3Cu14−δTe12 as well as its stability with regards to Cu ion movement. For the latter, two single crystals were picked from pellets after they were measured up to 573 and 673 K, which showed no significant changes in the occupancies of any of the Cu sites. All investigated Ba3Cu14−δTe12 materials displayed low thermal conductivity values (<1 W m–1 K–1) and appropriate electrical conductivity values (300–600 Ω–1 cm–1). However, the thermopower values were comparably low (<+65 μV K–1), resulting in uncompetitive zT values, with the highest being achieved for Ba3Cu13.175Te12, namely zT = 0.12 at 570 K. In an attempt to decrease the thermal conductivity, and thereby enhance the figure of merit, a brief alloying study with Ag was undertaken. The incorporation of Ag, however, did not produce any significant improvements.

Thermoelectric sulfides have recently attracted special attention because of the high availability and environmentally benign character of sulfur. In special cases such as in copper and silver sulfides with high ion mobility and thus high disorder, excellent thermoelectric performance can be achieved. However, stability is a high concern; the ion mobility may lead to device degradation over time. Here, we studied the stability of the canfieldite Ag8SnS6 under different measurement conditions. Without any precautionary measures, formation of Ag and or Ag2S wires was observed during the transport measurements on Ag8SnS6. This problem of lack of stability can be mitigated by restricting the maximum temperature to remain below 685 K. Increasing the Ag content enhances the performance by enlarging the electrical conductivity, but comes at the cost of lower stability. In that case, decreasing the current density was required to avoid this degradation. Such a limitation is practical in small-scale applications such as thin-film devices, but not in large-scale power generation applications.