Realizing a stable high thermoelectric zT ∼ 2 over a broad temperature range in Ge 1−x−y Ga x Sb y Te via band engineering and hybrid flash-SPS processing

Bhuvanesh Srinivasan 1, 2 Alain Gellé 3 Francesco Gucci 2 Catherine Boussard-Plédel 1 Bruno Fontaine 1 Régis Gautier 1 Jean-François Halet 1 Michael Reece 2 Bruno Bureau 1
1 ISCR - Institut des Sciences Chimiques de Rennes
2 QMUL - Queen Mary University of London
3 IPR - Institut de Physique de Rennes
Abstract : We report a remarkably high and stable thermoelectric figure of merit zT close to 2 by manipulating the electronic bands in Ga–Sb codoped GeTe, which has been processed by hybrid flash-spark plasma sintering. According to the experimental results and first-principles calculations, the vast enhancement achieved in the thermopower due to codoping of Ga (2 mol%) and Sb (8 mol%) in GeTe is attributed to a concoction of reasons: (i) suppression of hole concentration; (ii) improved band convergence by decreasing the energy separation between the two valence band maxima to 0.026 eV; (iii) Ga predominantly contributing to the top of the valence band in Ga–Sb codoped GeTe, despite the Ga-induced resonance state not being located at a favorable position near the Fermi level; (iv) active participation of several bands increasing the hole carrier effective mass; (v) facilitating band degeneracy by reducing the R3m → Fm[3 with combining macron]m structural transition temperature from 700 K to 580 K. The synergy between these complementary and beneficial effects, in addition to the reduced thermal conductivity, enabled the flash sintered Ge0.90Ga0.02Sb0.08Te composition to not only exhibit a peak of zT of ∼1.95 at 723 K, but also to maintain/stabilize its high performance over a broad temperature range (600–775 K), thus making it a serious candidate for mid-temperature range energy harvesting devices.
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Bhuvanesh Srinivasan, Alain Gellé, Francesco Gucci, Catherine Boussard-Plédel, Bruno Fontaine, et al.. Realizing a stable high thermoelectric zT ∼ 2 over a broad temperature range in Ge 1−x−y Ga x Sb y Te via band engineering and hybrid flash-SPS processing. Inorganic Chemistry Frontiers, Royal Society of Chemistry, 2018, 6 (1), pp.63-73. ⟨10.1039/C8QI00703A⟩. ⟨hal-01952889⟩

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