Novel bismuth-based Zintl phase makes efficient thermoelectric material

An international team led by researchers from the University of Houston (UH) has reported a record thermoelectric performance in rarely-studied bismuth-based Zintl phases, potentially leading to a new class of thermoelectric material.

The new material is non-toxic and can be used at temperatures between 500°C and 600°C. The research is described in a paper published in the Proceedings of the National Academy of Sciences.

Thermoelectric materials produce electricity by exploiting the flow of thermal current from a warmer area to a cooler area, and are currently used in both subsea and aerospace applications. Widespread adoption of this form of clean energy has been hampered, however, by the relatively low efficiency of available materials. Existing materials can only convert heat to electricity at a relatively low rate, which is determined by the figure of merit, or ZT.

Zintl compounds – a class of materials named after the German chemist Eduard Zintl, who developed the idea of a metal/non-metal compound – are considered potential candidates as thermoelectric materials. But bismuth-based Zintl compounds haven't been widely studied, said Zhifeng Ren, professor of physics at UH and lead author of the paper. Zintl materials in general are often overlooked as potential thermoelectric materials because they usually don't convert heat to electricity very efficiently, Ren said.

The researchers have now reported that the new material – with the chemical formula (Eu_0.5Yb_0.5)_1-xCa_xMg₂Bi₂ – has a figure of merit of 1.3 at 873K (600°C), higher than that recorded for antimony (Sb)-based Zintl compounds. That translates to an efficiency of about 10%, said Ren, who is also a principal investigator at the Texas Center for Superconductivity at UH. The highest efficiency achieved with current single thermoelectric materials is around 12%.

"This new Bi-based Zintl phase with high thermoelectric properties could be a good thermoelectric material candidate in the future," the researchers wrote.

In the paper, they describe using band engineering and multi-strain field fluctuation to enhance the figure of merit for the material. "This ZT value is the highest ever reported in a CaAl₂Si₂-based structure, especially compared to the most popular Sb-based Zintl compounds," they wrote. "We confirm chemical disorder has no effect on valence band, but does affect the conduction band, resulting in good p-type thermoelectric properties."

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.