Preparation and Characterization of High Temperature Thermoelectrics Based on Metal/Oxide Nanocomposites

Abstract

AbstractThermoelectric devices based on “n-type” oxide semiconductors and metal/oxide nanocomposites are being considered for high temperature thermocouples, heat flux sensors and energy harvesting devices. In terms of energy harvesting, preliminary 2D thermoelectric calculations indicated that enough electrical energy can be generated from the large thermal gradients that exist within a gas turbine engine to power active wireless devices. Several promising bi-ceramic junctions based on this concept were investigated in terms of their high temperature thermoelectric properties. The most promising bi-ceramic junction was based on indium tin oxide (ITO) and a NiCrCoAlY/alumina nanocomposite. The thermoelectric responses of these individual elements were evaluated relative to a platinum reference electrode. A maximum emf of 77 mV was achieved for a NiCrCoAlY/alumina nanocomposite/platinum thermocouple for an imposed temperature gradient of 1111 °C. The thermoelectric power for this couple was 78 μV/°C. When this NiCrCoAlY/alumina nanocomposite was combined with ITO to form a bi-ceramic junction, thermoelectric powers on the order of 700 μV/°C were obtained. A maximum electromotive force of 291mV was achieved for a hot junction temperature of 1100 °C. The thermoelectric response after repeated thermal cycling to 1200 °C was both repeatable and reproducible. The ITO was prepared in varying nitrogen, oxygen and argon partial pressures, which was used to control the charge carrier concentration, stability and thermoelectric response of the bi-ceramic junctions. The thermoelectric response decreased with increasing nitrogen partial pressure and increased with oxygen partial pressure in the plasma with the argon partial pressure constant. The relationship between the sputtering parameters and thermoelectric properties was investigated and the application of these bi-ceramic junctions as thermocouples and energy harvesting devices is discussed.