微結構協同機制對一碲化鍺 (GeTe)複合材料熱電表現的影響效應

Abstract

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Germanium Telluride (GeTe) has been extensively investigated among the lead-free thermoelectric (TE) materials for its high thermoelectric performance (ZT) in mid-temperature; however, high p-type carrier density (∼10^21 cm-3) weakens its suitability for higher ZT's. To strengthen the thermoelectric properties of nature-friendly GeTe, we utilized Molybdenum (Mo), a widely used transition element, for further study and confirmed its role in enhancing GeTe's TE properties. The density functional theory (DFT) calculations and TE transport properties experiments were performed to study the influence of Mo doping on the Ge site of the GeTe system. DFT computations predict the additional dopant/impurity states induced by Mo-doping. Mo doping sharply decreasedthe carrier concentration, e.g., from 8.28×10^20 cm-3 (pristine GeTe) to 5.24×10^20 cm-3 for Ge0.97Mo0.03Te with a slight increase in the Seebeck at room temperature. The simultaneous reduction in thermal conductivity is correlated with optimized carrier concentration, multi-scale lattice deformation, verified by extensive microstructural studies, emphasized by microcrystalline rods (MCRs), high-density planar defects, nano strained domains, strained stacking faults, point defects, herringbone, strengthening all-frequency phonon scattering.Moreover, co-doping of Sb/Bi with Mo at the Ge sites primarily decreases the carrier concentration (n) and thermal conductivity (κ) to achieve a higher ZT. The co-doping of Sb/Bi demonstrated a prominent role with a maximum ZT of ∼ 2.14 and ∼ 2.3 at 673 K for the samples of Ge0.89Mo0.01Sb0.1Te and Ge0.89Mo0.01Bi0.1Te, respectively. This work reports one of the highest TE performances among the transition metal co-doping in the mid-temperature range. The synergistic performance with an ultralow thermal conductivity has been achieved primarily due to microcrystalline-assisted grain boundary formations, a possible pathway for reducing the thermal conductivity. Different scattering centers in Mo doped GeTe systems, which helps the reduction in κlat, and overall thermal conductivity reached an ultralow, owing to a highly disordered network formation to hinder the phonon transport.