Thermoelectrics at Northwestern

The Snyder Group at Northwestern MSE continues to specialize in Thermoelectric Materials and Devices as well as expand into other Materials for Energy fields. Interested students are encouraged to apply to the top ranked MSE department at Northwestern University wtih many groups studying thermoelectrics including those run by Ken Poeppelmeier, Mercouri Kanatzidis, Chris Wolverton, Vinayak Dravid, David Dunand and others. We frequently have joint projects with NASA-Jet Propulsion Laboratory.

Eleonora Isotta wins ITS Postdoc Award 2024

For For her work with Thermal Imaging of Grain Boundaries.

Michael Toriyama wins ITS Graduate Student Award 2024
Weertman Fellowship 2023

For outstanding achievements as a Graduates Student in MSE at Northwestern.

Jeff Snyder wins ITS Outstanding Achievement and Humboldt Awards 2024

For outstanding contributions in the field of Thermoelectrics.

Leah Borgsmiller wins Best Presentation Award at MRS Fall 2022

For her Presentation on Low Thermal Conductivity and Thermoelectric Performance of Zintl Yb₁₀MnSb₉.

Perseverance Rover Powered by Thermoelectrics Lands on Mars

The newest Mars rover from NASA JPL uses PbTe-based thermoelectrics for power. Latest News and Video

Kazuki Imasato wins 2020 ITS Graudate Student Award

For his work optimizing the new n-type thermoelectric material Mg₃Sb₂ to be competitive with Bi₂Te₃.

Matthias Agne wins 2019 ITS and Gold MRS Graudate Student Awards

For his work elucidating the thermodynamics of heat capacity and diffuson thermal conductivity in complex materials.

Riley Hanus wins 2019 ITS Graudate Student Award

For his work developing the understanding of how microstructure (dislocations and grain boundaries) affects thermal transport by phonon scattering and strain softening.

Stephen Kang wins 2017 ITS Student Award

For his work on understanding the electronic transport using the generalized transport function, combining seebeck and conductivity experiments. Now a postdoc at Stanford U.

Yinglu Tang wins 2016 ITS Goldsmid Award

For her work on understanding the electronic structure and phase relations for optimizing Skutterdite thermoelectric materials. Yinglu is an assistant professor at TU Delft.

Sabah Bux (JPL) wins 2015 ITS Young Investigator Award

For her work on novel and nanostructured thermoelectric materials.

Heng Wang wins 2014 ITS Goldsmid Award

For his Ph.D. work on Band Engineering and PbSe. Now an assistant professor at Illinois Institute of Technology

Alex Zevalkink wins 2013 ITS Goldsmid Award

For her Ph.D. work on new Zintl phase thermoelectric materials. Alex is now an assistant professor at Michigan State University.

Yanzhong Pei wins 2013 ITS Young Investigator Award

For his work on band engineering of thermoelectric materials. Former Posdoc Yanzhong Pei (裴艳中) is Professor of Materials Science at Tonji University in Shanghai China.

Thermoelectric Materials from Zintl Compounds

The rich solid-state chemistry of Zintl phases enables a directed search and optimization of new complex thermoelectric materials including the new thermoelectric material Mg₃Sb₂, which is the first material to be competitive with State-of-the-art Bismuth Telluride (Bi₂Te₃) based materials in 60 years.

• “Improvement of Low‐Temperature zT in a Mg₃Sb₂–Mg₃Bi₂ Solid Solution via Mg‐Vapor Annealing” Advanced Materials  (2019)
• “Exceptional thermoelectric performance in Mg3Sb0.6Bi1.4 for low-grade waste heat recovery” Energy & Environmental Science 12, 965 (2019)
• "Phase Boundary Mapping to Obtain n-type Mg₃Sb₂-Based Thermoelectrics" Joule 2, 141 (2018)
• "Acchieving zT > 1 in Inexpensive Zintl Phase Ca9Zn4+xSb9 by Phase Boundary Mapping" Adv. Funct. Mater. 27, 1606361 (2017)
• "Zintl Chemistry for Designing High Efficiency Thermoelectric Materials" Chemistry of Materials, 22 p624 (2010)

Thermal Conductivity due to Dislocations and Grain Boundaries

Exceptionally low thermal conductivity good Peltier cooling performance was found in Bi₂Te₃-Sb₂Te₃ alloys hot pressed with liquid Te. The reduced thermal conductivity with only a small reduction in electron mobility can be explained by low energy grain boundaries consisting of dislocation arrays.

• “Phonon diffraction and dimensionality crossover in phonon-interface scattering” Communications Physics 1, (2018)
• "Lattice Dislocations Enhancing Thermoelectric PbTe in Addition to Band Convergence" Advanced Materials 29, 1606768 (2017)
• "Vacancy-induced dislocations within grains for high-performance PbSe thermoelectrics" Nature Communications 8, 13828 (2017)
• "Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics” Science, 348, 6230 (2015)
• “Dislocation strain as the mechanism of phonon scattering at grain boundaries” Materials Horizons  3, 234 (2016)

Charge Transport Model for Complex Conductors: Conducting Polymers, Correlated Electron Oxides and Grain Boundaries

A two parameter mathematical model that can explain the experimentally observed relationship between thermopower (Seebeck coefficient) and electrical conductivity can identify the charge transport mechanism. For example itinerant band conduction in SrTiO₃ or hopping, narrow band conduction in CeO₂. Thermally activated conductivity in polycrystalline materials may arise from grain boundary polarization effects. The model clearly identifies a different mechanism for conducting polymers, that may be an indication of percolation transport between conducting ordered regions (figure).

• “Quantifying charge carrier localization in chemically doped semiconducting polymers” Nature Materials 20, 1414 (2021)
• “Charge Transport Model for Conducting Polymers” Nature Materials 16, 252 (2017); Opinion
• "Grain boundary dominated charge transport in Mg₃Sb₃-based compounds" Energy & Envriomental Science 11, 429, (2018)
• "Thermopower-conductivity relation for distinguishing transport mechanisms: Polaron hopping in CeO₂ and band conduction in SrTiO₃" Physical Review B 97, 235201 (2018)

Liquid-Like Thermoelectric Materials

Because a liquid does not propagate shear vibrations the thermal conductivity can be less than that of a solid. Using the liquid-like behaviour of superionic conductors and related highly disordered materials extends the phonon-glass electron-crystal concept for the search for new thermoelectrics.

• Press Coverage: R&D Mag - Nanowerk - 中国科学院
• “Suppression of atom motion and metal deposition in mixed ionic/electronic conductors" Nature Communications 9, 2910 (2018)
• “High thermoelectric performance in non-toxic earth-abundant copper sulfide” Advanced Materials 26, 3974 (2014)
• "Liquid-like Copper Ion Thermoelectric Materials” Nature Materials, 11, 422 (2012)
• "Disordered Zinc in Zn₄Sb₃ with Phonon Glass, Electron Crystal Thermoelectric Properties" Nature Materials, Vol 3, p 458-463 (2004)
• more Cu2Se... , more Zn4Sb3...

Electronic Materials Physics for Energy Devices: Triboelectric, Piezoresistance and Flexible Thermoelectric Materials.

Triboelectrics When different materials are rubbed together there is a transfer of static electric charge known as Triboelectricity. Because of the charge separation and movement large voltages are produced, enough to cause sparking (static electricity discharge). The power produced from such Triboelectric Generatoris comes not from the rubbing but from the movement of electric charges from electric induction, resulting in direct conversion of mechanical energy to electrical energy.

• “A figure of merit for flexibility" Science 366, 690 (2019)
• “Optimization principles and the figure of merit for triboelectric generators" Science Advances 3, 8576 (2017)
• “Compliant and stretchable thermoelectric coils for energy harvesting in miniature flexible devices” Science Advances 4, (2018)
• “A Percolation Model for Piezoresistivity in Conductor-Polymer Composites” Advanced Theory and Simulations 2, (2019)

Band Structure Engineering Thermoelectrics

Alloys of PbTe and Bi₂Te₃ have been used to generate electricity from heat on NASA space missions for 50 years and now are being considered for use on Earth for automotive waste heat recovery. Our group has recently demonstrated that the zT of PbTe and PbSe alloys can be tuned to be much better than previously thought possible due, in part, to the exceptionally high valley degeneracy.

• Press Coverage: ScienceMag - PhysicsWorld - AmericanScientist - ArsTechnica
• “Lattice Softening Significantly Reduces Thermal Conductivity and Leads to High Thermoelectric Efficiency” Advanced Materials 31 1900108 (2019)
• “High thermoelectric performance in (Bi0.25Sb0.75)2Te3 due to band convergence and improved by carrier concentration control” Materials Today 20, 452 (2017)
• "Convergence of electronic bands for high performance bulk thermoelectrics" Nature 473, 66 (2011)
• "High thermoelectric figure of merit in heavy hole dominated PbTe" Energy and Environmental Science 4, 2085 (2011)