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Scientists claim a breakthrough in thermoelectric materials

03 April 2015

An international team of scientists from South Korea and the USA has reported a new method for creating a novel and much more efficient thermoelectric alloy.

The generation of dislocation arrays during the liquid-phase compaction process (illustration: Institute for Basic Science)

French physicist Jean Charles Athanase Peltier discovered a key concept necessary for thermoelectric (TE) temperature control in 1834. His findings were so significant, TE devices are now commonly referred to as Peltier devices. Since his work, there have been steady advancements in materials and design. Despite the technological sophistication Peltier devices, they are still 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 electrical input was only slightly less than the heat output. Since the 1960's there have been incremental advancements in alloy technology used in Peltier devices. In this latest work, the researchers* have formulated a new method for creating a novel and much more efficient TE alloy.

TE alloys are special because the metals have an incredibly high melting point, so they are combined instead via sintering. In their study, the 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, excess Te being expelled in the process.

By creating the alloy this way, the joints between the fused grains (the grain boundaries) took on a special property. Traditionally sintered Bi0.5Sb1.5Te3 have thick, coarse joints which have led to a decrease in both thermal and electrical conductivity. 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 320K within the range of 1.86 ±0.15 at 320K (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 results are also significant. The new material was able achieve a temperature change of 81K at 300K (26.85°C).

The applications for such a material are abundant. As new fabrication techniques are developed, Peltier cooling devices may be used in place of traditional compression refrigeration systems, as well as systems that provide localised power generation and cooling for personal electronic devices.

*The team included researchers from the IBS Centre for Integrated Nanostructure Physics (South Korea), 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 the Materials Science department, California Institute of Technology.

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