AsianScientist (Apr. 9, 2015) – A joint South Korean and American research group has developed a scalable production method for an alloy used in solid state thermoelectric devices. This new alloy is nearly twice as efficient as existing materials and could see applications in refrigeration, consumer electronics and transportation. The study describing the method has been published in Science.
Thermoelectric or Peltier devices are heat pumps that are able to transfer heat energy depending on the direction of the current. Because they are highly stable and can be precisely controlled, thermoelectric devices are currently used in products such as thermal cyclers for polymerase chain reaction (PCR) and digital cameras to reduce thermal noise. Despite the technological advantages, thermoelectric devices are much more expensive to produce and less energy efficient than traditional compressor/evaporation cooling.
In the 1960’s, Peltier devices were primarily made from Bismuth-Telluride (Bi2Te3) or Antimony-Telluride (Sb2Te3) alloys and had a peak efficiency (zT) of 1.1, meaning the electricity going in was only slightly less than the heat coming out.
In 2014, researchers in South Korea at IBS Center for Integrated Nanostructure Physics along with Samsung Advanced Institute of Technology, the Department of Nano Applied Engineering at Kangwon National University, the Department of Energy Science at Sungkyunkwan University and Materials Science department at California Institute of Technology California, formulated a new method for creating a much more efficient thermoelectric alloy.
Thermoelectric alloys are special because the metals have an incredibly high melting point. Instead of melting the metals to fuse them, they are combined through a process called sintering which uses heat and/or pressure to join the small, metallic granules. Traditionally sintered Bi0.5Sb1.5Te3 have thick, coarse joints which have led to a decrease in both thermal and electrical conductivity.
Instead, the joint research team used a process called liquid-flow assisted sintering which combined all three antimony, bismuth and telluride granules into one alloy (Bi0.5Sb1.5Te3). Additional melted tellurium was used as the liquid between the Bi0.5Sb1.5Te3 granules to help fuse them into a solid alloy and excess Te is expelled in the process.
By creating the alloy this way, the joints between the fused grains, also known as the grain boundaries, took on a special property. The new liquid-phase sintering creates grain boundaries which are organized and aligned in seams called dislocation arrays. These dislocation arrays greatly reduce their thermal conduction, leading to an enhancement of their thermoelectric conversion efficiency.
In tests, the efficiency (zT) reached 2.01 at 320 K within the range of 1.86 ±0.15 at 320 K (46.85 °C) for 30 samples, nearly doubling the industry standard. When the melt spun Bi0.5Sb1.5Te3 alloy is used in a Peltier cooler, the new material was able achieve a temperature change of 81 K at 300 K (26.85 °C).
As new fabrication techniques are developed, Peltier cooling devices may be used in place of traditional compression refrigeration systems. More importantly, as electrical vehicles and personal electronic devices become more ubiquitous in our daily lives, it is becoming increasingly necessary to have more efficient systems for localized electrical power generation and effective cooling mechanisms.
The article can be found at: Kim et al. (2015) Dense Dislocation Arrays Embedded In Grain Boundaries For High-performance Bulk Thermoelectrics.
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Source: Institute for Basic Science; Photo: p.Gordon/Flickr/CC.
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