Maths converges on a better thermoelectric material

It is a high-entropy ‘Zintl’ alloy of the form Yb_xCa_1-xMg_yZn_2-ySb₂, for which the team devised a way to calculate the exact proportions by aiming for band convergence.

“It is normally difficult to get high performance from thermoelectric materials because not all of the electronic bands in a material contribute,” said director of the university’s superconductivity centre Zhifeng Ren. “It’s even more difficult to make a complex material where all of the bands work at the same time in order to get the best performance.”

He likens band conversion to many people lifting an object – if they are a similar height, the load is carried more evenly, said Ren.

The chosen material has four parent compounds made from five elements: ytterbium, calcium, magnesium, zinc and antimony. The calculations showed which combinations of the parent compounds could reach band convergence, and the best combination was turned into a device.

This was tested in a lab-made instrument, and found to remain stable for at least two years.

“Without this method, you would have to experiment and try all possibilities,” said fellow researcher Xin Shi. “Now, we do a calculation first, we design a material, and then make it and test it.”

The calculation method is applicable to other potentially-thermoelectic multi-compound alloys, according to the university.

University of Houston worked with Rice University. Their work is described in the Science paper ‘Global band convergence design for high-performance thermoelectric power generation in Zintls‘

Image: University of Houston’s Zhifeng Ren (left), Xin Shi (centre) and Shaowei Song (right) with their lab-made energy conversion efficiency instrument.