Researchers discover tin selenide is best at converting waste heat to electricity
One strategy for addressing the world's energy crisis is to stop wasting so much energy when producing and using it, which can happen in coal-fired power plants or transportation. Nearly two-thirds of energy input is lost as waste heat.
Now Northwestern University scientists have discovered a surprising material that is the best in the world at converting waste heat to useful electricity. This outstanding property could be exploited in solid-state thermoelectric devices in a variety of industries, with potentially enormous energy savings.
An interdisciplinary team led by inorganic chemist Mercouri G. Kanatzidis found the crystal form of the chemical compound tin selenide conducts heat so poorly through its lattice structure that it is the most efficient thermoelectric material known. Unlike most thermoelectric materials, tin selenide has a simple structure, much like that of an accordion, which provides the key to its exceptional properties.
The efficiency of waste heat conversion in thermoelectrics is reflected by its figure of merit, called ZT. Tin selenide exhibits a ZT of 2.6, the highest reported to date at around 650 degrees Celsius. The material's extremely low thermal conductivity boosts the ZT to this high level, while still retaining good electrical conductivity.
The ZT metric represents a ratio of electrical conductivity and thermoelectric power in the numerator (which needs to be high) and thermal conductivity in the denominator (which needs to be low).
Potential areas of application for the high-temperature thermoelectric material include the automobile industry (a significant amount of gasoline's potential energy goes out of a vehicle's tailpipe), heavy manufacturing industries (such as glass and brick making, refineries, coal- and gas-fired power plants) and places where large combustion engines operate continuously (such as in large ships and tankers).
"A good thermoelectric material is a business proposition -- as much commercial as it is scientific," said Vinayak P. Dravid, a senior researcher on the team. "You don't have to convert much of the world's wasted energy into useful energy to make a material very exciting. We need a portfolio of solutions to the energy problem, and thermoelectric materials can play an important role."
Dravid is the Abraham Harris Professor of Materials Science and Engineering at the McCormick School of Engineering and Applied Science.
Details of tin selenide, probably among the world's least thermally conductive crystalline materials, are published today (April 17) by the journal Nature.
The discovery comes less than two years after the same research group broke the world record with another thermoelectric material they developed in the lab with a ZT of 2.2.
"The inefficiency of current thermoelectric materials has limited their commercial use," said Kanatzidis, the Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences. "We expect a tin selenide system implemented in thermoelectric devices to be more efficient than other systems in converting waste heat to useful electricity."
The material, despite having a very simple structure, conducts heat so poorly that even moderate thermoelectric power and electrical conductivity are enough to provide high thermoelectric performance at high temperature.
The researchers did not expect to find tin selenide to be such a good thermoelectric material.
"Lidong Zhao, the first author of the paper, deserves a lot of credit for looking at tin selenide," said Kanatzidis, who also holds a joint appointment at Argonne National Laboratory. "He is a good example of the curious people we try to attract to Northwestern."
Zhao, a postdoctoral fellow in Kanatzidis' research group, grew crystals of tin selenide and measured the crystal in three directions, along each axis. He found that the thermal conductivity was "ridiculously low" along the a-axis but also along the other two axes.
"The results are eye-opening because they point in a direction others would not look," Dravid said. "This material has the potential to be applied to other areas, such as thermal barrier coatings."
Kanatzidis and Zhao identified the potential of the material intuitively by looking at its crystal structure. They confirmed its exceptional thermoelectric properties and then turned to Dravid and Christopher M. Wolverton to uncover how the crystal was behaving and why.
"We found that the bonds between some atoms in this compound are very weak and lead to exceptionally soft, floppy atomic vibrations," said Wolverton, a senior author of the paper and a professor of materials science at the McCormick School.
Wolverton, an expert in computational materials science related to energy applications, showed that the accordion-like structure and weak bonds lead to atoms that vibrate very slowly.
"These very weak vibrations are responsible for the inability of the material to conduct heat," Wolverton said. "Our theory provides the scientific basis as to why the material behaves the way it does and also provides us with a new direction to search for even higher-efficiency materials."
"Tin selenide reminds us of that popular TV commercial for a memory foam mattress in which a person can jump on one side of the mattress while a glass of wine a few feet away is unperturbed -- the vibrations do not reach the glass because of the mattress' material," Kanatzidis said.
"Similarly, in tin selenide, heat cannot travel well through this material because its soft, accordion-like structure doesn't transmit vibrations well," he said. "One side of tin selenide gets hot -- where the waste heat is, for example -- while the other side remains cool. This enables the hot side to generate useful electricity."
"Our discovery underscores why the Department of Energy EFRC program works," Kanatzidis said. "A multidisciplinary team, such as ours, can look at a problem from many different angles, with sustained funding increasing the chances of a scientific breakthrough. And we have a special ambience here -- the spirit of Northwestern is interdisciplinary."
The paper is titled "Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals." In addition to Kanatzidis, Dravid, Wolverton and Zhou, other authors of the paper are Yongsheng Zhang and Gangjian Tan, of Northwestern, and Hui Sun and Ctirad Uher, of the University of Michigan.
Megan Fellman | Eurek Alert!
Researchers printed graphene-like materials with inkjet
18.08.2017 | Aalto University
Superconductivity research reveals potential new state of matter
17.08.2017 | DOE/Los Alamos National Laboratory
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
18.08.2017 | Life Sciences
18.08.2017 | Physics and Astronomy
18.08.2017 | Information Technology