S. Korean/US team develops new production method for inexpensive and more efficient thermoelectric materials
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 CalTech have developed a new method for creating a novel and much more efficient thermoelectric bismuth antimony telluride (Bi0.5Sb1.5Te3) alloy.
In tests reported in a paper in the journal Science, the efficiency (zT) reached 2.01 at 320 K (46.85 ˚C) within the range of 1.86 ±0.15 at 320 K for 30 samples, nearly doubling the industry standard. When the melt spun alloy is used in a Peltier cooler, the results are also significant. The new material was able achieve a temperature change of 81 K at 300 K (26.85° C).
The performance of thermoelectric materials is evaluated with a dimensionless figure of merit (zT) dependent on the Seebeck coefficient; electrical conductivity;and lattice thermal conductivity; and absolute temperature (T).
Introducing dislocation arrays at grain boundaries has the potential to improve zT by decreasing thermal conductivity, but dislocation arrays formed by traditional sintering techniques also decrease electrical conductivity. By modifying a traditional liquid-phase sintering technique, we avoid this pitfall and provide a different pathway for fabricating bulk alloys with high zT.—Kim et al.
The metals in TE alloys have a 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. The joint team, including IBS researchers, 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 granules to help fuse them into a solid alloy; excess liquid Te is expelled in the process.
|Generation of dislocation arrays at grain boundaries in Bi0.5Sb1.5Te3. Kim et al. Click to enlarge.|
By creating the alloy this way, the joints between the fused grains, also known as 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.
The present liquid-phase compaction method assisted with a transient liquid flow is highly scalable for commercial use and generally applicable to other thermoelectric systems such as PbTe, CoSb3, and Si-Ge alloys, and even engineer thermal properties of other thermal materials such as thermal barrier coatings. This may accelerate practical applications of thermoelectric systems in refrigeration and beyond to waste heat recovery and power generation.—Kim et al.
Sang Il Kim, Kyu Hyoung Lee, Hyeon A. Mun, Hyun Sik Kim, Sung Woo Hwang, Jong Wook Roh, Dae Jin Yang, Weon Ho Shin, Xiang Shu Li, Young Hee Lee, G. Jeffrey Snyder, Sung Wng Kim (2015) “Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectric” Science doi: 10.1126/science.aaa4166