Complete Characterization of Thermoelectric Materials by Impedance Spectroscopy

Abstract

Thermoelectric materials can directly convert waste heat into electricity. Due to the vast amount of energy available as waste heat in our society, these materials could contribute to reduce our dependence on fossil fuels and their associated environmental problems. However, the heat to electricity conversion efficiency of thermoelectric materials is still a limiting factor, and extensive efforts are being undertaken to improve their performance. The search for more efficient materials is focused on the optimization of three properties (Seebeck coefficient, electrical resistivity, and thermal conductivity). Typically, these are determined as function of temperature through independent measurements on two or more instruments, making thermoelectric characterization tedious and time consuming, which complicates the attainment of a more efficient heat to electricity energy conversion. Here, it is demonstrated for the first time that a complete thermoelectric characterization of a material may be achieved from a single electrical measurement performed on one instrument only, by employing the impedance spectroscopy method. A skutterudite sample is used for the demonstration, which is sandwiched between two stainless steel contacts in a four-probe arrangement and their properties are determined from 50 to 250 oC. This new approach shows good precision and agrees with characterization of the same sample performed with commercial equipment, illustrating the power of the technique to facilitate the rapid and efficient evaluation of thermoelectric materials.