Jan 18 2019
Leveraging the latest developments in applying hypothetical calculations to predict the characteristics of novel materials, scientists have discovered an innovative class of half-Heusler thermoelectric compounds, which also include a compound with the highest figure of merit—a metric used for establishing the way a thermoelectric material efficiently changes heat to electricity.
It maintained the high figure of merit at all temperatures, so it potentially could be important in applications down the road.
Zhifeng Ren, Physicist, Director, Texas Center for Superconductivity, University of Houston
Ren is also the corresponding author of a study reported in Nature Communications.
In the research community, thermoelectric materials have attracted a great deal of interest as a promising source of “clean” power, generated when the material transforms heat into electricity. This heat is usually waste heat produced by power plants or other similar industrial processes.
Although several potential materials have been identified, the majority of them have not been able to satisfy all of the needs for extensive commercial applications. According to the researchers, their discovery of half-Heusler compounds containing iron, antimony, and tantalum produced outcomes that are “quite promising for thermoelectric power generation.”
The team determined the conversion efficiency of a single compound at 11.4%—that means the material generated 11.4 W of electricity for each 100 W of heat it absorbed. According to Ren, who is also the M.D. Anderson Chair professor of physics at UH, hypothetical calculations indicate that the efficiency may reach 14%. He also observed that several thermoelectric devices, with a conversion efficiency of 10%, will have practical uses.
Ultimately, the team predicted six formerly unreported compounds and effectively produced one, which provided high performance without using costly elements.
“We have discovered 6 undocumented compounds and 5 of them are stable with the half-Heusler crystal structure,” the researchers wrote. “The p-type TaFeSb-based half-Heusler, one of the compounds discovered in this work, demonstrated a very promising thermoelectric performance.”
Apart from Ren and his lab members, the study involved additional investigators at UH; the Massachusetts Institute of Technology; the University of Missouri; Southwest University in Chongqing, China; Beijing National Laboratory for Condensed Matter Physics at the Chinese Academy of Sciences; the University of Electronic Science and Technology of China; the Institute for Metallic Materials in Dresden, Germany; and Shanghai University.
The use of hypothetical calculations to predict compounds anticipated to possess high thermoelectric performance enabled the scientists to zero in on the most favorable compounds. However, actually producing materials containing iron, antimony, and tantalum, an effort headed by first authors Jun Mao and Hangtian Zhu and UH post-doctoral researchers, was shown to be difficult partly because the components possess extremely different physical characteristics.
For instance, tantalum has a melting point above 3,000 ºC, whereas antimony has a melting point of 630 ºC. While tantalum is tough, antimony is comparatively soft, making arc melting—a standard technique of integrating materials—more complicated. However, the researchers were able to develop the compound through a combination of hot pressing and ball milling.
After forming the compound, the scientists disclosed that it provided the required physical properties and also the mechanical properties that would guarantee structural integrity. The elements utilized are all comparatively available and cheap, rendering the compound cost-effective, said Ren.
Besides the characteristics of the compound itself, the investigators said that their results provide robust support for further dependence on computational techniques to guide 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,” the researchers wrote. “As such, it might be beneficial to use more sophisticated theoretical studies in predicting compounds before devoting the efforts for careful experimental study.”
Apart from Ren, Mao, and Zhu, co-authors of the study include Qing Zhu, Zihang Liu, Tian Tong, and Jiming Bao, all from UH; Yuwei Li, Jifeng Sun, Yuhao Fu, and David J. Singh from the University of Missouri; Yumei Wang from the Beijing National Laboratory for Condensed Matter Physics at the Chinese Academy of Sciences; Guannan Li from Southwest University in Chongqing, China; Qichen Song, Jiawei Zhou, and Gang Chen from MIT; Ran He, Andre Sotnikov, and Kornelius Nielsch from the Institute for Metallic Materials in Dresden, Germany; Zhiming Wang and Wuyang Ren of the University of Electronic Science and Technology of China; and Jun Luo and Li You of Shanghai University.