Scientists at Northwestern University have discovered a very interesting material known to be the number one in the world at waste heat conversion into electricity. This useful property can be used in many thermoelectric devices and in various industrial sectors where exists the potential to save big quantities of wasted energy.
Tin Selenide discovered by a chemist
The material was discovered by an interdisciplinary team led by the inorganic chemist Mercouri G. Kanatzidis. They found that the crystal form of the chemical compound named tin solenoid has the ability to conduct heat very poorly and because of this feature it is considered the most effective thermoelectric material known to man by now.
Unlike other thermoplastic materials, tin solenoid has a very basic structure, similar to the structure of an accordion, which is the key to its remarkable properties.
The efficiency obtained while converting waste heat into electricity it is shown by its figure of merit, called ZT.
The ZT metric shows a ratio of electrical conductivity and thermoelectric power in the numerator which must be high and the thermal conductivity in the denominator must be low.
A material featuring high electrical conductivity
Tin selenide displays a ZT of 2.6, the biggest value reported to this day at around 650 degrees Celsius. The product has incredibly low thermal conductivity and that is the reason for the increased ZT value to such higher level, while still maintaining excellent electrical conductivity.
This wonderful thermoelectric material has numerous applications in the auto industry, in the heavy manufacturing sector and in areas where huge combustion engines run continuously (like big ships and tankers). This research group had another discovery two years ago, when they broke the world record with another thermoelectric material developed in their laboratory which had a ZT of 2.2.
Despite the materials extremely simple structure, it can conduct heat so badly that even moderate thermoelectric power and electrical conductivity are quite enough to supply high thermoelectric efficiency at high temperatures.
The scientists did not expect for the tin selenide to be such an excellent thermoelectric material.
Who gets the credit for the discovery?
Zhao, a postdoctoral scientist in Kanatzidis’ group, should have all the credit for looking at this material (tin selenide) while growing crystals of tin selenide and measuring the crystal in three directions, along each axis. He discovered that the thermal conductivity was extremely low along the a-axis and also the other two axis.
Zhao and Kanatzidis determined the capacity of the material without effort by looking at its crystal structure. They validated the remarkable thermoelectric properties and afterwards turned to Dravid and Christopher M. Wolverton to reveal exactly why the crystal is behaving this way.
Wolverton, a specialist in computational materials science associated with energy applications, revealed that the accordion-like structure and weak bonds result in atoms that vibrate extremely slow and that is the reason that it not heats even at high temperatures.
Conclusion
Finally, Kanatzidis mentioned that a multidisciplinary group like theirs, can investigate a problem from numerous and various angles, with sustained financing that enhancing the possibilities of a scientific development.
These achievements are all possible due to the favorable a unique ambience present in the group and due to the interdisciplinary spirit of the Northwestern University.
