A new method for the evaluation of thermoelectric materials

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Working with one of the world’s leading researchers in thermoelectric materials, a team of researchers in the Clemson Department of Physics and Astronomy and the Clemson Nanomaterials Institute (CNI) has developed a new, noninvasive method for evaluating thermoelectric materials.

Associate Professor in the Department of Physics and Astronomy Sribarna Bhattacharya, Engineer Herbert Pehlo and Founding Director of CNI Apparao Rao have collaborated with world-renowned researcher HJ Goldsmid, Professor Emeritus at the University of New South Wales (UNSW) in Sydney, Australia, to create a one-stop method for evaluating the efficiency of refractory materials.

Goldsmid is considered by many to be the “father of thermoelectricity” for his pioneering work in thermoelectric materials. Bhattacharya first contacted Goldsmid on LinkedIn, telling him that she had confirmed one of his theoretical predictions during her graduate studies at Clemson University.

Later, Bhattacharya shared a paper she wrote with Rao after she joined his research group. Goldsmid mentioned to her that he had a new method in mind for studying electrothermal and shared his one-page theory with her. He was 89 years old at the time and enthusiastically began collaborating with CNI researchers because he considered Bhattacharya to be part of his research “family”.

Thermoelectric materials use a temperature gradient (DT) to generate electricity. They can be used to generate energy by converting heat into electricity (Sebeck method) or cooling by converting electricity into refrigeration (Peltier method). Thermoelectric materials are used in applications ranging from NASA space missions to seat heaters and coolers in vehicles.

A material’s thermoelectric efficiency is measured by its number of merit, or zT, which takes into account the material’s temperature, electrical conductivity, and thermal conductivity. The traditional method for determining zT requires two measurements using different sets of equipment, something that sometimes causes researchers to report incorrect results.

In other words, researchers sometimes mistakenly measure electrical conductivity (the flow of charges) and thermal conductivity (the flow of heat) along different directions in their sample when switching from one device to another.

Peltier cooling has not previously been used to evaluate zT due to the high DT, or the maximum achievable temperature difference between the cold junction and the ambient. “We used metal-junction thermocouples and semiconductors to reduce the DT to a much narrower range so that the temperature-dependent zT can be determined with greater accuracy,” said Bahlo.

“The idea of ​​using a metal and a semiconductor to reduce the DT was hidden in plain sight until Professor Goldsmid realized this was the case and proposed this new method for measuring zT,” Behlow added.

“The experimental setup we developed at CNI (with the help of the Department of Physics and Astronomy Instruments) to test Professor Goldsmid’s theory ensures that charge flow and heat flow are measured in the same direction in the sample,” Rao said. “Therefore, by design, our method provides an accurate zT.”

Isabel Ranko, a high school student at the South Carolina Governor’s School of Science and Mathematics, also contributed to the study. Ranko, who worked with the team through Clemson’s summer research intern program, independently verified the model calculations reported by Bahlo.

The bismuth telluride sample used in the study was synthesized by Senior Lecturer in the Department of Physics and Astronomy Pooja Punnett as part of her PhD research.

The UNSW-Clemson Study “Thermal Merit Character of Peltier Cooling” was published in November in Journal of Applied Physics. It was chosen as an “Editor’s Pick”, which the team considers to be a tribute to Goldsmid.

more information:
S. Bhattacharya et al, Character of thermoelectric merit of Peltier cooling, Journal of Applied Physics (2022). doi: 10.1063/5.0116327

Provided by Clemson University

the quote: A New Method for Evaluating Thermoelectric Materials (2023, January 9) Retrieved January 10, 2023 from https://phys.org/news/2023-01-method-thermoelectric-materials.html

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