Microstructural design of thermoelectric materials

Microstructural design of thermoelectric materials

Thermoelectric materials can convert largely untapped heat energy sources, e.g. geothermal or industrial waste heat, into sustainable electricity. Despite their high potential, efficient thermoelectrics are rare. High thermoelectric conversion efficiency requires high electrical conductivity (σ) but low thermal conductivity (κ), a rare combination in materials. Using materials science principles, these transport properties can be tailored by microstructural defects.

High grain-boundary density in thermoelectrics can suppress κ, but often yields a lower σ, which compromises the overall efficiency. Hence, we identify grain boundary engineering to obtain high σ as a promising way to optimize the performance. We employ atomic-resolution microscopy and spectroscopy to investigate the grain boundary phases, in order to understand their impact on electrical transport. In our pioneering work, grain boundary phases with HCP-stacking are identified in a NbFeSb half-Heusler (FCC) thermoelectric [1]. The grain boundary electrical conductivity is greatly improved as the grain boundary defect phase transitions from FeSb-enriched to a TiSb-enriched defect phase. Building on this concept, we have designed InSb as a grain boundary dopant to selectively improve the grain boundary conductivity, as In has practically no solubility in NbFeSb [2, 3]. We have also demonstrated that grain boundaries with dopant segregation can serve as conductive pathways for electrical transport, reaping both benefits of high σ and low κ for fine-grained TiCoSb thermoelectrics [4].

Beside grain boundaries, we also investigate the effect of dislocations, stacking faults, and precipitates on the transport properties. An important aspect is how the microstructure evolves during thermoelectric operation at elevated temperatures. We employ correlative microscopy to study processes such as Ostwald ripening [5] and crystallization [6], as well as in situ microscopy to understand mechanisms behind dynamic changes in carrier concentrations [7] and dislocation-phonon scattering [8].

Project publications

Bueno Villoro, R.; Zavanelli, D.; Jung, C.; Mattlat, D. A.; Naderloo, R. H.; Pérez, N. A.; Nielsch, K.; Snyder, G. J.; Scheu, C.; He, R. et al.; Zhang, S.: Grain Boundary Phases in NbFeSb Half-Heusler Alloys: A New Avenue to Tune Transport Properties of Thermoelectric Materials. Advanced Energy Materials 13 (13), 2204321 (2023)
Bueno Villoro, R.; Naderloo, R. H.; Mattlat, D. A.; Jung, C.; Nielsch, K.; Scheu, C.; He, R.; Zhang, S.: Composite design of half-Heusler thermoelectrics: Selective doping of grain boundary phases in NbFeSb by InSb. Materials Today Physics 38, 101240 (2023)
Naderloo, R.H.; Bueno Villoro, R.; Mattlat, D.A.; Ying, P.; Song, S.; Bayesteh, S.; Nielsch, K.; Scheu, C.; Ren, Z.; Zhu, H.; Zhang, S.; He, R.
Performance advancements in P-type TaFeSb-based thermoelectric materials through composition and composite optimizations
Energy & Environmental Science (2025), DOI: 10.1039/D4EE04819A
Bueno Villoro, R.; Wood, M.; Luo, T.; Bishara, H.; Abdellaoui, L.; Zavanelli, D.; Gault, B.; Snyder, G. J.; Scheu, C.; Zhang, S.: Fe segregation as a tool to enhance electrical conductivity of grain boundaries in Ti(Co,Fe)Sb half Heusler thermoelectrics. Acta Materialia 249, 118816 (2023)
Yu, Y.; Sheskin, A.; Wang, Z.; Uzhansky, A.; Natanzon, Y.; Dawod, M.; Abdellaoui, L.; Schwarz, T.; Scheu, C.; Wuttig, M. et al.; Cojocaru-Mirédin, O.; Amouyal, Y.; Zhang, S.: Ostwald Ripening of Ag2Te Precipitates in Thermoelectric PbTe: Effects of Crystallography, Dislocations, and Interatomic Bonding. Advanced Engineering Materials 14 (19), 2304442 (2024)
Jung, C.; Zhang, S.; Cheng, N.; Scheu, C.; Yi, S.-H.; Choi, P.-P.: Effect of Heat Treatment Temperature on the Crystallization Behavior and Microstructural Evolution of Amorphous NbCo1.1Sn. ACS Applied Materials and Interfaces 15 (39), pp. 46064 - 46073 (2023)
Yu, Y.; Zhou, C.; Zhang, X.; Abdellaoui, L.; Doberstein, C.; Berkels, B.; Ge, B.; Qiao, G.; Scheu, C.; Wuttig, M. et al.; Cojocaru-Mirédin, O.; Zhang, S.: Dynamic doping and Cottrell atmosphere optimize the thermoelectric performance of n-type PbTe over a broad temperature interval. Nano Energy 101, 107576 (2022)
Abdellaoui, L.; Chen, Z.; Yu, Y.; Luo, T.; Hanus, R.; Schwarz, T.; Bueno Villoro, R.; Cojocaru-Mirédin, O.; Snyder, G. J.; Raabe, D. et al.; Pei, Y.; Scheu, C.; Zhang, S.: Parallel Dislocation Networks and Cottrell Atmospheres Reduce Thermal Conductivity of PbTe Thermoelectrics. Advanced Functional Materials 31 (20), 2101214 (2021)

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