"[The thermoelectric material] maintained the high figure of merit at all temperatures, so it potentially could be important in applications down the road."Zhifeng Ren, University of Houston

Taking advantage of recent advances in using theoretical calculations to predict the properties of new materials, an international team of researchers has reported the discovery of a new class of half-Heusler thermoelectric compounds. One of these compounds has a record high figure of merit – a metric used to determine how efficiently a thermoelectric material can convert heat to electricity.

"It maintained the high figure of merit at all temperatures, so it potentially could be important in applications down the road," said physicist Zhifeng Ren, director of the Texas Center for Superconductivity at the University of Houston (TcSUH) and corresponding author of a paper on this work in Nature Communications.

Thermoelectric materials have generated increasing interest in the research community as a potential source of ‘clean’ power, through their ability to convert heat – often waste heat generated by power plants or other industrial processes – into electricity.

A number of promising thermoelectric materials have been discovered, although most have been unable to meet all of the requirements for widespread commercial applications. The researchers said their discovery of half-Heusler compounds composed of tantalum, iron and antimony yielded results that are "quite promising for thermoelectric power generation".

The researchers measured the conversion efficiency of one compound at 11.4% – meaning the material produced 11.4 watts of electricity for every 100 watts of heat it took in. Theoretical calculations suggest its efficiency could reach 14%, said Ren, who is also professor of physics at UH. He noted that many thermoelectric devices will have practical applications with a conversion efficiency of 10%.

In all, the researchers predicted six previously unreported compounds and successfully synthesized one, which delivered high performance without the use of expensive elements.

"We have discovered six undocumented compounds and five of them are stable with the half-Heusler crystal structure," they wrote. "The p-type TaFeSb-based half-Heusler, one of the compounds discovered in this work, demonstrated a very promising thermoelectric performance."

Relying on theoretical calculations to predict compounds expected to have high thermoelectric performance allowed the researchers to home in on the most promising compounds. But actually creating materials composed of tantalum, iron and antimony, an effort led by UH post-doctoral researchers and first authors Hangtian Zhu and Jun Mao, proved complex, partly because the components have such disparate physical properties.

Tantalum, for example, has a melting point above 3000°C, while the melting point of antimony is 630°C. Tantalum is hard, while antimony is relatively soft, making arc melting – a common method of combining materials – more difficult. The researchers were able to make the compound using a combination of ball milling and hot pressing.

Once the compound was formed, the researchers said it offered both the physical properties needed, as well as the mechanical properties that would ensure structural integrity. Ren said the elements used are all relatively available and inexpensive, making the compound cost-effective.

In addition to the properties of the compound itself, the researchers said their results offer strong support for further reliance on computational methods to direct experimental efforts.

"It should be noted that careful experimental synthesis and evaluation of a compound are costly, while most theoretical calculations, especially as applied in high throughput modes, are relatively inexpensive," they wrote. "As such, it might be beneficial to use more sophisticated theoretical studies in predicting compounds before devoting the efforts for careful experimental study."

This story is adapted from material from the University of Houston, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.