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Unified mobility model for grain‑boundary‑limited transport in polycrystalline thermoelectric materials
Singh, Sukhwinder Stoeva, Zlatka
Singh, Sukhwinder
Stoeva, Zlatka
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2025-09-12
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Under embargo until 12/09/2026
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Abstract
Grain-boundary-limited charge transport is a fundamental bottleneck in polycrystalline thermoelectric materials, where reduced carrier mobility degrades electrical conductivity and suppresses power factors. This degradation arises from the interplay of scattering mechanisms: grain-boundary barriers dominate at low temperatures; thermionic activation enables partial barrier crossing at intermediate temperatures; and phonon scattering limits the mean free path at high temperatures. Hence, there remains a need for a physically transparent framework to quantitatively extract these microstructural parameters. In this study, a semi-empirical mobility model that explicitly integrates these grain-boundary mechanisms was developed and validated, expressed as: μ<inf>eff</inf>(T)=μ<inf>w</inf>exp(−[Formula presented] where μ<inf>w</inf> is the weighted mobility, Φ<inf>GB</inf> is the grain‑boundary barrier height, k<inf>B</inf> is Boltzmann's constant, T is temperature, l(T) is the bulk mean free path and w<inf>GB</inf> is the boundary width. This model was validated for oxide semiconductor, intermetallic, chalcogenide and heuslers polycrystalline materials, achieving excellent agreement with experimental data (R<sup>2</sup>= 0.97–0.99) and yielding physically consistent parameters: Φ<inf>GB</inf> ≈ 0–0.056 eV and l<inf>300</inf> ≈ 6–368 nm. A case study for Ta doped ZnO thermoelectric material shows that barrier passivation (reduction of Φ<inf>GB</inf> from 0.056 eV to 0.03 eV) combined with modest grain-interior improvement (l<inf>300</inf>→60 nm) can significantly enhance carrier mobility across the entire temperature range. The analysis predicts that, at ∼1000 K, grain engineering could nearly double mobility and electrical conductivity. Consequently, tailoring microstructural features enable a power factor approximately of 7.64x10<sup>−4</sup>Wm<sup>−1</sup>K<sup>−2</sup> at 1000 K, compared with the reported value of 4x10<sup>−4</sup>Wm<sup>−1</sup>K<sup>−2</sup>. This framework provides concrete, process-addressable targets for grain-boundary engineering and mobility-driven performance gains.
Citation
Yusuf, G.T., Singh, S., Askounis, A., Stoeva, Z. and Tchuenbou-Magaia, F. (2025) Unified mobility model for grain‑boundary‑limited transport in polycrystalline thermoelectric materials. Materialia, 44, 102550.
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Journal article
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en
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This is an author's accepted manuscript of an article that has been published by Elsevier on 12/09/2025, available online: https://doi.org/10.1016/j.mtla.2025.102550
The accepted manuscript may differ from the final published version.
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2589-1529
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2589-1529
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This work was supported by the Centre for Engineering Innovation at the University of Wolverhampton. Partial support was also provided by the ReACTIVE Too project, funded through the European Union’s Horizon 2020 Research and Innovation Staff Exchange Programme (Marie Skłodowska-Curie Actions, Grant Agreement No 871163), as well as by the Tertiary Education Trust Fund (TETFund) in collaboration with Osun State Polytechnic, Iree, Nigeria.