A fresh approach to assessing thermoelectric materials

 By Clemson University 

Jan 10 2023

                            A group of scientists from the Clemson Department of Physics and Astronomy and the Clemson Nanomaterials Institute (CNI) have created a brand-new, foolproof way to assess thermoelectric materials in collaboration with one of the world's leading experts in the field.

Engineer Herbert Behlow, CNI Founding Director Apparao Rao, and Department of Physics and Astronomy Research Assistant Professor Sriparna Bhattacharya worked with eminent scientist H. J. Goldsmid, professor emeritus at the University of New South Wales (UNSW) in Sydney, Australia, to develop a one-stop method for assessing the effectiveness of thermoelectric materials.

Because of his groundbreaking work with thermoelectric materials, Goldsmid is often regarded as the "father of thermoelectrics." Bhattacharya initially got in touch with Goldsmid via LinkedIn and informed him that during her graduate studies at Clemson University, she had verified one of his theoretical hypotheses.

After joining Rao's study team, Bhattacharya later presented a paper she had written with him. Goldsmid presented his one-page idea with her and said that he had a novel approach in mind for investigating thermoelectrics. He gladly began working with the CNI researchers at the age of 89 because he saw Bhattacharya as a member of his own scientific "family."

A temperature gradient (DT) is used by thermoelectric materials to produce power. By turning heat into electricity (Seebeck technique), they may be used to generate power, or by converting electricity into cooling, they can be used to generate power (Peltier method). Applications for thermoelectric materials range from NASA space missions to seat warmers and coolers in automobiles.

A figure-of-merit, or zT, which takes into account the material's temperature, electrical conductivity, and thermal conductivity, is used to assess the effectiveness of thermoelectric materials. The conventional approach to zT determination needs two measurements with distinct sets of instruments, which occasionally leads to researchers reporting false results.

In other words, when a sample is shifted from one instrument to another, researchers may inadvertently detect thermal conductivity (heat flow) and electrical conductivity (charge flow) along distinct directions in the sample.

Because of a high DT, or the highest attainable difference in temperature between the cold junction and ambient, peltier cooling has not been employed previously for analysing zT. We reduced the DT to a considerably narrower range using thermocouples with a metal and semiconductor junction, according to Behlow, so that the temperature dependent zT could be identified with greater precision.

"Until Professor Goldsmid realised that this was the case and offered this novel way for measuring zT, the notion to utilise a metal and a semiconductor to minimise DT was concealed in plain sight," Behlow continued.

The experimental set-up that CNI created (with assistance from the Department of Physics and Astronomy Instrument Shop) ensures that the charge flow and the heat flow are detected in the sample's identical direction. Therefore, our technique delivers correct zT by design.

The study also included contributions from Isabel Rancu, a high school student at the South Carolina Governor's School for Science and Mathematics. The model calculations published by Behlow were independently confirmed by Rancu, a research intern from Clemson University who collaborated with the team throughout the summer.

Pooja Puneet, a senior lecturer in the Department of Physics and Astronomy, created the bismuth telluride sample utilised in the study as part of her PhD work.

The thermoelectric figure-of-merit from Peltier cooling UNSW-Clemson work was released in November in the Journal of Applied Physics. The group saw their selection as a "editor's pick" as a respect to Goldsmid.