| A new computer-controlled high temperature thermoelectric transport measurement system was built for investigating new high temperature quaternary thermoelectric materials and devices. Such thermoelectric materials are desirable for power generation applications—converting thermal energy to electricity. Some of the advantages of thermoelectric devices include no moving parts, solid-state construction, environmentally friendliness, and high reliability. An increasing concern of environment and awareness of limited resources has made waste heat recovery an urgent global issue.; The high temperature thermoelectric system is computer-controlled by LabVIEW™ programming with extensive PID temperature control. It can be used to characterize the thermoelectric power (S) and electrical conductivity (σ) of electronic materials in a broad temperature range (80–800K). The figure of merit, ZT (= S2σT/κ), is used to define the efficiency of thermoelectric materials. The measured power factor (S2σ) can be used to identify good candidates for thermoelectric applications. Some of the new quaternary materials exhibit power factor larger than 30 μW/K2·cm in a wide temperature range of 300–600K. Since these materials are expected to have very low thermal conductivity at high temperatures, a ZT of approaching or larger than 1 at high temperatures can be achieved. Three of the best thermoelectric materials: bismuth telluride alloys, lead telluride alloys and silicon-germanium, have a ZT of ∼1 at their optimum temperatures. The experimental results also reveal the new quaternary materials as narrow-band gap semiconductors with metallic behavior.; The theory behind thermoelectric materials will be reviewed; this includes the search of materials with large band degeneracy or high anisotropy, the parameters that can enhance the B-factor, and the coefficient of performance as well as the efficiency of the thermoelectric devices. The structural design and automated features of the measurement system will be presented. The technique of material/device characterization will be discussed as well as the results of investigations on new quaternary materials and devices constructed with these materials. |
