We demonstrate the potential of metallurgical controlling of the phase separation reaction, by means of spark plasma sintering consolidation and subsequently controlled heat treatments sequence, for ...enhancement the thermoelectric properties of the p‐type Ge0.87Pb0.13Te composition. Very high ZTs of up to ∼2, attributed to the nucleation of sub‐micron phase separation domains and to comparable sized twinning and dislocation networks features, were observed. Based on the experimentally measured transport properties, combined with the previously reported phase separated n‐type (Pb0.95Sn0.05Te)0.92(PbS)0.08 composition, a maximal efficiency value of ∼11.5% was theoretically calculated. These ZT and efficiency values are among the highest reported for single composition non‐segmented bulk material legs.
Highly efficient PbTe based thermoelectric materials are reported with maximal ZT values of ∼2, due to phase separation reactions resulted in sub‐micro thermodynamically driven features. The reported materials are among the most efficient thermoelectric bulk materials ever reported.
Thermoelectric heat-to-power generation is an attractive option for robust and environmentally friendly renewable energy production. Historically, the performance of thermoelectric materials has been ...limited by low efficiencies, related to the thermoelectric figure-of-merit ZT. Nanostructuring thermoelectric materials have shown to enhance ZT primarily via increasing phonon scattering, beneficially reducing lattice thermal conductivity. Conversely, density-of-states (DOS) engineering has also enhanced electronic transport properties. However, successfully joining the two approaches has proved elusive. Herein, we report a thermoelectric materials system whereby we can control both nanostructure formations to effectively reduce thermal conductivity, while concurrently modifying the electronic structure to significantly enhance thermoelectric power factor. We report that the thermoelectric system PbTe–PbS 12% doped with 2% Na produces shape-controlled cubic PbS nanostructures, which help reduce lattice thermal conductivity, while altering the solubility of PbS within the PbTe matrix beneficially modifies the DOS that allow for enhancements in thermoelectric power factor. These concomitant and synergistic effects result in a maximum ZT for 2% Na-doped PbTe–PbS 12% of 1.8 at 800 K.
Iron pyrite is an earth-abundant and inexpensive material that has long been interesting for electrochemical energy storage and solar energy conversion. A large-scale conversion synthesis of ...phase-pure pyrite nanowires has been developed for the first time. Nano-pyrite cathodes exhibited high Li-storage capacity and excellent capacity retention in Li/pyrite batteries using a liquid electrolyte, which retained a discharge capacity of 350 mAh g(-1) and a discharge energy density of 534 Wh kg(-1) after 50 cycles at 0.1 C rate.
The reduction of thermal conductivity, and a comprehensive understanding of the microstructural constituents that cause this reduction, represent some of the important challenges for the further ...development of thermoelectric materials with improved figure of merit. Model PbTe‐based thermoelectric materials that exhibit very low lattice thermal conductivity have been chosen for this microstructure–thermal conductivity correlation study. The nominal PbTe0.7S0.3 composition spinodally decomposes into two phases: PbTe and PbS. Orderly misfit dislocations, incomplete relaxed strain, and structure‐modulated contrast rather than composition‐modulated contrast are observed at the boundaries between the two phases. Furthermore, the samples also contain regularly shaped nanometer‐scale precipitates. The theoretical calculations of the lattice thermal conductivity of the PbTe0.7S0.3 material, based on transmission electron microscopy observations, closely aligns with experimental measurements of the thermal conductivity of a very low value, ∼0.8 W m−1 K−1 at room temperature, approximately 35% and 30% of the value of the lattice thermal conductivity of either PbTe and PbS, respectively. It is shown that phase boundaries, interfacial dislocations, and nanometer‐scale precipitates play an important role in enhancing phonon scattering and, therefore, in reducing the lattice thermal conductivity.
Spinodal decomposition phase separation in the thermoelectric PbTe0.7S0.3 system is shown to generate dislocations, boundaries, and nanometer‐scale precipitates that are effective in reducing lattice thermal conductivity. Calculations of lattice thermal conductivity from advanced transmission electron microscopy analysis are in close agreement with experimentally measured values of lattice thermal conductivity.
Silicon is an extremely important technological material, but its current industrial production by the carbothermic reduction of SiO2 is energy intensive and generates CO2 emissions. Herein, we ...developed a more sustainable method to produce silicon nanowires (Si NWs) in bulk quantities through the direct electrochemical reduction of CaSiO3, an abundant and inexpensive Si source soluble in molten salts, at a low temperature of 650 °C by using low‐melting‐point ternary molten salts CaCl2–MgCl2–NaCl, which still retains high CaSiO3 solubility, and a supporting electrolyte of CaO, which facilitates the transport of O2− anions, drastically improves the reaction kinetics, and enables the electrolysis at low temperatures. The Si nanowire product can be used as high‐capacity Li‐ion battery anode materials with excellent cycling performance. This environmentally friendly strategy for the practical production of Si at lower temperatures can be applied to other molten salt systems and is also promising for waste glass and coal ash recycling.
From old glass to batteries: A new and more sustainable method to produce Si nanowires in bulk quantities through the direct electrochemical reduction of CaSiO3 at a low temperature of 650 °C was developed. The method uses the low‐melting‐point ternary molten salts of CaCl2–MgCl2–NaCl, which retain high CaSiO3‐solubility, and a supporting electrolyte of CaO, which drastically improves the reaction kinetics and enables the electrolysis at low temperatures.
We have investigated the possible mechanisms of phonon scattering by nanostructures and defects in PbTe-X (X = 2% Sb, Bi, or Pb) thermoelectric materials systems. We find that among these three ...compositions, PbTe-2% Sb has the lowest lattice thermal conductivity and exhibits a larger strain and notably more misfit dislocations at the precipitate/PbTe interfaces than the other two compositions. In the PbTe-Bi 2% sample, we infer some weaker phonon scattering BiTe precipitates, in addition to the abundant Bi nanostructures. In the PbTe-Pb 2% sample, we also find that pure Pb nanoparticles exhibit stronger phonon scattering than nanostructures with Te vacancies. Within the accepted error range, the theoretical calculations of the lattice thermal conductivity in the three systems are in close agreement with the experimental measurements, highlighting the important role of misfit dislocations, nanoscale particles, and associated interfacial elastic strain play in phonon scattering. We further propose that such particle-induced local elastic perturbations interfere with the phonon propagation pathway, thereby contributing to further reduction in lattice thermal conductivity, and consequently can enhance the overall thermoelectric figure of merit.
Higher manganese silicides (HMS) made of earth‐abundant and non‐toxic elements are regarded as promising p‐type thermoelectric materials because their complex crystal structure results in low lattice ...thermal conductivity. It is shown here that the already low thermal conductivity of HMS can be reduced further to approach the minimum thermal conductivity via partial substitution of Mn with heavier rhenium (Re) to increase point defect scattering. The solubility limit of Re in the obtained RexMn1‐xSi1.8 is determined to be about x = 0.18. Elemental inhomogeneity and the formation of ReSi1.75 inclusions with 50−200 nm size are found within the HMS matrix. It is found that the power factor does not change markedly at low Re content of x ≤ 0.04 before it drops considerably at higher Re contents. Compared to pure HMS, the reduced lattice thermal conductivity in RexMn1‐xSi1.8 results in a 25% increase of the peak figure of merit ZT to reach 0.57 ± 0.08 at 800 K for x = 0.04. The suppressed thermal conductivity in the pure RexMn1‐xSi1.8 can enable further investigations of the ZT limit of this system by exploring different impurity doping strategies to optimize the carrier concentration and power factor.
The lattice thermal conductivity of higher manganese silicides (HMS) is primarily suppressed by rhenium substitution to approach the calculated minimum lattice thermal conductivity value. This leads to improved thermoelectric performance in the Re‐substituted HMS as compared to pure HMS.
We show experimentally the direct reduction in lattice thermal conductivity as a result of in situ nanostructure generation within a thermoelectric material. Solid solution alloys of the ...high-performance thermoelectric PbTe−PbS 8% can be synthesized through rapid cooling and subsequent high-temperature activation that induces a spontaneous nucleation and growth of PbS nanocrystals. The emergence of coherent PbS nanostructures reduces the lattice thermal conductivity from ∼1 to ∼0.4 W/mK between 400 and 500 K.
Semiconducting higher manganese silicides (HMS), with a nominal composition of MnSi1.73, are particularly promising thermoelectric materials because of their elemental abundance, nontoxicity, and ...reported ZT of around 0.4 at 800 K for undoped samples. However, embedded MnSi impurities naturally form during the melt growth of HMS materials. The influences of such naturally occurring MnSi impurities within bulk HMS have yet to be carefully studied. Herein, we report the synthesis of high-purity MnSi-free single crystals of HMS by chemical vapor transport and the thermoelectric properties of consolidated HMS samples prepared by spark plasma sintering (SPS). The high purity of the HMS crystals is verified by scanning and transmission electron microscopy, electron diffraction, and synchrotron high-resolution X-ray diffraction. Despite successfully growing high purity HMS single crystals, we find that MnSi will nevertheless precipitate from HMS after SPS processing. In-situ sychrotron high-resolution X-ray diffraction experiments show that HMS are unstable at high temperatures. Despite the precipitation of MnSi inclusions within the HMS materials, we show that samples prepared from undoped single crystals of HMS exhibit higher hole mobilities owing to their higher purity, resulting in an improved maximum ZT of 0.52 ± 0.08 at 750 K.
The incorporation of PbSnS2 in PbTe results in a tremendous reduction of the lattice thermal conductivity to 0.8 W/mK at room temperature, a reduction of almost 60% over bulk PbTe. Transmission ...electron microscopy reveals very high density displacement layers, misfit dislocations, and phase boundaries. Our thermal transport calculations based on modified Debye‐Callaway model, well in agreement with the experimental measurements, reveal that the layer structured PbSnS2 plays an important role in reducing the lattice thermal conductivity.
