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Microstructure manipulation plays an important role in enhancing physical and mechanical properties of materials. Here a high figure of merit zT of 1.2 at 357 K for n‐type bismuth‐telluride‐based thermoelectric (TE) materials through directly hot deforming the commercial zone melted (ZM) ingots is reported. The high TE performance is attributed to a synergistic combination of reduced lattice thermal conductivity and maintained high power factor. The lattice thermal conductivity is substantially decreased by broad wavelength phonon scattering via tuning multiscale microstructures, which includes microscale grain size reduction and texture loss, nanoscale distorted regions, and atomic scale lattice distotions and point defects. The high power factor of ZM ingots is maintained by the offset between weak donor‐like effect and texture loss during the hot deformation. The resulted high zT highlights the role of multiscale microstructures in improving Bi2Te3‐based materials and demonstrates the effective strategy in enhancing TE properties.

Zn potential, high Zn abundancy, and ease of material handling. In particular, the recent demonstrations of a reversible charging/discharging process with the use of neutral electrolyte have further rekindled strong research interest in ZIB as potential secondary battery. [5][6][7] However, one key challenge in ZIB research is the highly selective cathode material. To date, only a handful of materials such as manganese-based oxides, [8][9][10] vanadium-based oxides, [11][12][13] Prussian blue analogs, [14,15] polyanion compounds, [16] and quinone analogs [17] have been reported as viable ZIB cathode. Out of these materials, MnO 2 is highly favored as ZIB cathode due to its environmental benignity, low cost, and ease of fabrication. As a result, numerous Zn/MnO 2 battery systems have been reported with satisfactory electrochemical performances over the recent years. [18][19][20][21][22] However, such progress has gradually decelerated due to the increasing challenge in enhancing the intrinsic MnO 2 capacity through modifying with different MnO 2 polymorphs, [23,24] or widening the interlayer spacing. [25] This decelerated trend suggests that structural enhancements have eventually reached a bottleneck, and an alternative strategy such as modifying the material surface chemistry should be considered as the next stage in Zn/MnO 2 battery electrochemical performance enhancements.Defect engineering is a powerful technique that can imbue a material with new functionalities such as electronic, magnetic, and optical properties. [26][27][28] Among the different types of defects, oxygen vacancy (V O ) is a particularly important one in modifying the surface chemistry and geometrical configuration of oxides. [29][30][31] Oxygen vacancy can influence the Zn 2+ adsorption on the material surface, whereby the calculated Gibbs free energy of Zn 2+ adsorption provides an estimation gauging the ease of Zn 2+ adsorption/desorption, i.e., reversibility. Our simulation results show that Gibbs free energy of Zn 2+ adsorption on MnO 2 surface is significantly altered when oxygen vacancies are generated into the MnO 2 lattice. Pristine MnO 2 demonstrates a thermodynamically more favorable Zn 2+ adsorption due to its lower Gibbs free energy of Zn 2+ adsorption. However, this phenomenon concurrently hints that the subsequent desorption process would be thermodynamically more unfavorable. This means that, for pristine MnO 2 , once Zn 2+ is adsorbed onto the MnO 2 surface, the strong chemical bonds between Zn and O would hinder the subsequent Zn 2+ desorption process and these undesorbed Zn 2+ A major limitation of MnO 2 in aqueous Zn/MnO 2 ion battery applications is the poor utilization of its electrochemical active surface area. Herein, it is shown that by generating oxygen vacancies (V O ) in the MnO 2 lattice, Gibbs free energy of Zn 2+ adsorption in the vicinity of V O can be reduced to thermoneutral value (≈0.05 eV). This suggests that Zn 2+ adsorption/desorption process on oxygen-deficient MnO 2 is more reversible as compared to pr...

As a lead-free material, GeTe has drawn growing attention in thermoelectrics, and a figure of merit (ZT) close to unity was previously obtained via traditional doping/alloying, largely through hole carrier concentration tuning. In this report, we show that a remarkably high ZT of ∼1.9 can be achieved at 773 K in Ge0.87Pb0.13Te upon the introduction of 3 mol % Bi2Te3. Bismuth telluride promotes the solubility of PbTe in the GeTe matrix, thus leading to a significantly reduced thermal conductivity. At the same time, it enhances the thermopower by activating a much higher fraction of charge transport from the highly degenerate Σ valence band, as evidenced by density functional theory calculations. These mechanisms are incorporated and discussed in a three-band (L + Σ + C) model and are found to explain the experimental results well. Analysis of the detailed microstructure (including rhombohedral twin structures) in Ge0.87Pb0.13Te + 3 mol % Bi2Te3 was carried out using transmission electron microscopy and crystallographic group theory. The complex microstructure explains the reduced lattice thermal conductivity and electrical conductivity as well.