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Oxides are of interest for thermoelectrics due to their high thermal stability, chemical inertness, low cost, and eco‐friendly constituting elements. Here, adopting a unique synthesis route via chemical co‐precipitation at strongly alkaline conditions, one of the highest thermoelectric performances for ZnO ceramics (PFmax=$PF_{\text{max}} =$ 21.5 µW cm−1 K−2 and zTmax=$zT_{\text{max}} =$ 0.5 at 1100 K in Zn0.96Al0.04O${\rm Zn}_{0.96} {\rm Al}_{0.04}{\rm O}$) is achieved. These results are linked to a distinct modification of the electronic structure: charge carriers become trapped at the edge of the conduction band due to Anderson localization, evidenced by an anomalously low carrier mobility, and characteristic temperature and doping dependencies of charge transport. The bi‐dimensional optimization of doping and carrier localization enable a simultaneous improvement of the Seebeck coefficient and electrical conductivity, opening a novel pathway to advance ZnO thermoelectrics. [ABSTRACT FROM AUTHOR]

Bismuth chalcogenides are promising materials for thermoelectric (TE) application due to their high power factor (product of the square of the Seebeck coefficient and electrical conductivity). However, their high thermal conductivity is an issue of concern. Single doping has proven to be useful in improving TE performance in recent years. Here, it is shown that dual isovalent doping shows the synergistic effect of thermal conductivity reduction and electron density control. The insertion of large atoms in the layered Bi2Te3 structure distorts the crystal lattice and contributes significantly to phonon scattering. The ultralow thermal conductivity (KT = 0.35 W m−1 K−1 at 473 K) compensates for the low power factor and thus enhances TE performance. The density functional theory electronic structure calculation results reveal deep defects states in the valence band, which influences the electronic transport properties of the system. Therefore, the dual dopants (indium and antimony) show a coupled effect of improvement in the density of state near the Fermi level and reduction in the conduction band minimum, thus enhancing electron density. Numerically, it is demonstrated that the dual doping favors acoustic phonon scattering and thus drastically reduces the thermal conductivity. [ABSTRACT FROM AUTHOR]

Composite thermoelectric materials based on skutterudite represent an interesting subject for the synthesis and study of their thermoelectric properties. The introduction of oxide additives typically reduces the cost of the product and can positively affect the mechanical properties and thermal stability of the material. In this work, a high-performance composite skutterudite (InCo 4 Sb 12) + x wt.% (ZnO) (x = 0, 1, 2.7 and 7.4) was obtained by a combination of induction melting and planetary ball milling. Bulk composites with a density of 90 % were obtained by spark plasma sintering. In contrast to the results reported in previously published works, in this case there was an increase in thermal conductivity, which was associated with the formation of agglomerates of highly thermally conductive oxide phases. The figure of merit zT reaches 1.41 at 700 K for the reference sample InCo 4 Sb 12 , and 1.28 for the composite with embedded ZnO inclusions. Despite a 9 % decrease in the zT, the best composite InCo 4 Sb 12 /ZnO demonstrates an increase in hardness of 18 % and reduction in the cost of raw materials. [ABSTRACT FROM AUTHOR]

We report a numerical study of the field assisted sintering of silicon germanium alloys by a finite element method, which takes into account contact resistances, thermal expansion and the thermoelectric effect. The distribution of electrical and thermal fields was analyzed numerically, based on the experimental data collected from spark plasma sintering (SPS) apparatus. The thermoelectric properties of Si-Ge used within the simulation were considered as the function of density and the sintering temperature. Quantitative estimation of the temperature distribution during the sintering pointed to a significant, up to 60 °C, temperature difference within the specimen volume for the case of the sintering temperature at 1150 °C. [ABSTRACT FROM AUTHOR]

We report on thermoelectric properties of layered misfit cobaltites Ca 3− x Na x Co 4 O 9− x F x ( x = 0, 0.3, 0.45, 0.6) prepared by a two steps solid state reaction route followed by spark plasma sintering. Structural characterization revealed that a minor amount of Co 3 O 4 is presented in all the samples as an impurity phase. Besides, a trace of NaF phase was detected in the sample with x = 0.6 which can be an indication of the solubility limit of NaF into Ca 3 Co 4 O 9 . Measurements of electrical resistivity and Hall effect showed that double substitution of Ca 2+ by Na + and O 2− by F − results in a decrease of the electrical resistivity which is due to an increase in the carrier concentration. Thermal conductivity of Ca 3− x Na x Co 4 O 9− x F x decreases with increasing temperature which is due to the enhancement of the phonon scattering at high temperatures and slightly increases with x which is caused by the increase in the carrier concentration and the growth of the mean grain size in the doped samples. Seebeck coefficient S of Ca 3− x Na x Co 4 O 9− x F x is positive in the whole temperature range measured. At high temperatures (above 800 K) value of S in the x = 0.3 and x = 0.45 samples exceeds that in the pristine sample. Thermoelectric figure of merit ZT = 0.13 was achieved at 873 K, which is of about 20% higher than that in the pristine Ca 3 Co 4 O 9 . [ABSTRACT FROM AUTHOR]

Herein, we demonstrate that BiCuSeO compound can be formed in bulk directly from the raw materials through reactive spark plasma sintering (RSPS) followed by ball milling and a second short spark plasma sintering step. Compared to BiCuSeO samples obtained by a conventional solid-state reaction, the electrical transport properties of the RSPS bulk were moderately affected by the sintering technique, while the lattice thermal conductivity was almost unaffected, and the figure of merit zT attained a value at 773 K comparable to state-of-the-art BiCuSeO. The results indicate a new scalable method for the preparation of oxyselenides. Image, graphical abstract [ABSTRACT FROM AUTHOR]

ZnO has potential as a thermoelectric material for high-temperature applications, but its performance is limited by the strong interconnection between electrical and thermal transportation. In this study we proved that ZnO bulk samples produced from cost-effective and environmentally friendly nitrates via ultrasonic spray pyrolysis and modified chemical precipitation methods followed by spark plasma sintering, demonstrate significantly higher thermoelectric performance than those fabricated from commercially available ZnO powder. To further explore the potential of the developed chemical precipitation technique, we synthesized a series of Al-doped samples with a nominal composition of Zn 1– x Al x O (x = 0.02, 0.04, 0.06). The substitutuion of Al into the ZnO structure led to two significant effects: (i) a partial substitution of Zn with Al boosts the power factor; (ii) the formation of the ZnAl 2 O 4 spinel phase acting as scattering center for phonons in addition to the mass and strain fluctuations induced by the partial Zn-Al substitution, both leading to the thermal conductivity reduction. As a result, Al doping led to a threefold enhancement of the thermoelectric performance with z T value of ∼0.12 achieved at 1100 K for the Zn 0.94 Al 0.06 O sample. • ZnO ceramics fabricated via ultrasonic spray pyrolysis and chemical precipitation. • Obtained samples exhibit higher degree of disorder and thus increased μ w. • Al doping of ZnO leads to a threefold increase of thermoelectric performance. • A z T value of ∼0.12 achieved for the Zn 0.94 Al 0.06 O sample at 1100 K. [ABSTRACT FROM AUTHOR]

• For the first time, composites made of SiGe and MnTe were investigated. • MnTe enhances the electrical conductivity and reduces the lattice thermal conductivity. • The maximum value of zT for Si 80 Ge 20 B 2 + 4 wt% MnTe was 0.8 at 1000 K. We report on a study of bulk SiGe-MnTe composites obtained via spark plasma sintering of mixed powders composed of SiGe that was fabricated by mechanical alloying and MnTe prepared via solid-state reaction. The presence of MnTe in the SiGe matrix led to an increase in the electrical conductivity by ∼ 50 % and a decrease in the lattice thermal conductivity of the samples by ∼ 28 %, while the Seebeck coefficient was reduced from 252 μV K−1 to 197 μV K−1 at 1000 K. As a result, the peak zT of 0.75 was obtained for pristine Si 80 Ge 20 B 2 , and 0.8 for Si 80 Ge 20 B 2 + 4 wt% MnTe at 1000 K. [ABSTRACT FROM AUTHOR]

Abstract Bi 1- x Nd x CuSeO (x = 0; 0.05; 0.10; 0.15) was fabricated by the solid-state reaction and the reactive spark plasma sintering for comparative study. It was demonstrated that BiCuSeO could be formed in-situ by the reaction between Bi 2 O 3 , Bi, Cu and Se during the densification process. The effect of Nd doping on the thermoelectric properties has been investigated. The results indicated that for both series of the samples the substitution of Bi3+ by Nd3+ resulted in the increase of charge carrier concentration mainly caused by Bi/Cu deficiencies formation with the substitution. However, the specimens obtained by reactive spark plasma sintering had lower hole concentration which may originate from the high speed of the process resulted in induced point defect and interface scattering and another phase formation mechanism leading to the smaller amount of Bi/Cu deficiencies. Highlights • Nd substituted BiCuSeO oxyselenides were fabricated by reactive spark plasma sintering. • Effect of Bi to Nd substitution on the properties of BiCuSeO has been studied. • By Bi to Nd substitution, Bi and Cu deficiencies formed. • Samples obtained by RSPS exhibited the isotropic behaviour of transport properties. [ABSTRACT FROM AUTHOR]

We report on thermoelectric properties of low Ge content n -type Si 0.9 Ge 0.1 –Mg 2 Si nanocomposite. Introduction of the Mg 2 Si phase into a SiGe matrix resulted in a dramatic drop of the lattice thermal conductivity beyond the previously reported lowest limit for SiGe alloys due to intensification of phonon scattering on SiGe–Mg 2 Si grain boundaries. For a sample doped with 1 at.% of Mg 2 Si, the peak value of thermoelectric figure of merit ZT reached ~ 0.8 at 800 °C. Sintered nanocomposites still exhibit high thermoelectric performance while being almost two times cheaper than Si 0.8 Ge 0.2 . [ABSTRACT FROM AUTHOR]

We report on thermoelectric properties of p -type boron doped nanostructured bulk Si 80 Ge 20 synthesized via spark plasma technique. We demonstrate that the presence of a limited amount of nanometer-sized SiO 2 inclusions, resulting from the oxidation during processing stages is an effective way to further thermal conductivity reduction in the nanostructured Si 80 Ge 20 alloys. Significant reduction of thermal conductivity and high values of Seebeck coefficient allowed us to reach a peak ZT value of about 0.72 at 800 °C in boron doped Si 80 Ge 20 . [ABSTRACT FROM AUTHOR]

Among layered oxygen-containing compounds, BiCuSeO is one of the most promising candidates for thermoelectric applications due to its intrinsically low thermal conductivity and good thermal stability. However, the rather poor electrical conductivity of pristine BiCuSeO hinders its potential. Further enhancement of the thermoelectric performance by single doping at Bi site is limited mainly due to dramatic decrease of carrier mobility. Thus, new strategies, such as dual doping or doping with variable-valence elements seem to be promising. Along with that, the development of a fast and scalable synthesis route is essential for the industrial-scale fabrication of thermoelectric materials. Hence, in this paper, Bi 1– x Sm x CuSeO samples (0 ≤ x ≤ 0.08) have been synthesized with a simple and scalable reactive sintering process. For comparison, Bi 1– x Sm x CuSeO oxyselenides were also obtained by the conventional solid-state route. Our results highlight that, Sm for Bi substitution increases the electrical conductivity by 1.5–2 times and decreases the Seebeck coefficient by ~1.4 times at 873 K for both series. Overall, considering the increase of lattice thermal conductivity upon doping and not optimized power factor, the figure of merit z T is reducing upon doping. • Sm-doped BiCuSeO oxyselenides fabricated by reactive sintering. • Sm doping leads to an increase of σ from 39 Ω–1 cm–1 to ~55 Ω–1 cm–1 at 873 K. • Quality factor is reduced upon Sm doping due to increase in κ and decrease of μ w. [ABSTRACT FROM AUTHOR]

Heusler alloys have attracted much attention due to their low toxicity, mechanical and thermal stability, relative abundance, and potential for thermoelectric power generation. Herein, we demonstrate that TiFe 2 Sn full-Heusler alloy can be obtained by a mechanochemical synthesis of metal precursors followed by spark plasma sintering. It is shown that thus prepared samples exhibit the ordered structure (Heusler phase, MnCu 2 Al-type). The influence of processing parameters on microstructure, phase composition, and thermoelectric properties of TiFe 2 Sn is studied. The thermoelectric figure of merit of the sample fabricated under optimal mechanochemical processing parameters is comparable to that of TiFe 2 Sn synthesized using the conventional route. Thus, our results indicate that the mechanochemical synthesis is a facile, scalable, and cost-effective route for the preparation of TiFe 2 Sn Heusler alloys. • TiFe 2 Sn prepared by mechanochemical synthesis followed by spark plasma sintering. • Mechanochemical synthesis performed at room temperature. • Figure of merit similar to that of TiFe 2 Sn synthesized by a conventional path. [ABSTRACT FROM AUTHOR]

Recognizing high thermoelectric performance in semiconducting materials is a challenging task. This is because the Seebeck coefficient and electrical conductivity which constitute the thermoelectric power factor are unfavourably coupled. This means decoupling the transport properties of thermoelectric materials to enhance the power factor without compromising the thermal conductivity is essential. Herein we report that the substitution of erbium (Er) within bismuth selenide (Bi 2 Se 3) results in a simultaneous enhancement in Seebeck coefficient and electrical conductivity via effective mass and Fermi energy optimization. The Er-Substitution in Bi 2 Se 3 does not only promote a simultaneous increase in Seebeck coefficient and electrical conductivity but also decreases the thermal conductivity through an enhancement in phonon scattering. Consequently, the optimum composition is found for the Bi 1 · 85 Er 0 · 15 Se 3 sample instigating that, minimal substitution amount is required to optimize the thermoelectric performance. Our numerical calculation also shows that Er substitution alters the Fermi energy of the Bi 2 Se 3 TE materials, thereby enhancing the effective mass. Through Raman and XPS characterization, we also elucidate that Er substitution does not change the chemical structure and chemical bonding of the pristine material appreciably. It thus leads to improvement in the Seebeck coefficient and electrical conductivity via effective mass optimization. This unique work presents a facile, scalable, cost-effective, and controllable synthesis of nanostructured Bi 2 Se 3 toward realizing high-performance thermoelectric devices. Image 1 • A facile synthesis of high purity erbium substituted Bi 2 Se 3 thermoelectric material. • This study elucidates a mechanism of simultaneous enhancement in Seebeck coefficient and electrical conductivity through isovalent substitution. • Numerical discussion of the effect of the erbium substitution on the Fermi energy as evidence of the Seebeck coefficient and electrical conductivity decoupling is shown. • Systematic analysis of the structural, morphology and thermoelectric properties of the Er substituted Bi 2 Se 3 is related. [ABSTRACT FROM AUTHOR]

• Pure BiCuSeO phase doped and undoped prepared by high-energy ball milling. • BiCuSeO phase formation mechanism during high-energy ball milling studied. • BiCuSeO phase was formed 5 times faster than that by a mechanical alloying. • Synthesis performed under ambient atmosphere at room temperature. We report on the direct ultrafast synthesis of Pb-doped BiCuSeO oxyselenides by high-energy ball milling. We show that, contrary to the mechanical alloying sintering routes used in the previous reports which require 7–13 h to fabricate the BiCuSeO phase in powder form, this synthesis technique enables us to obtain pure phase materials at room temperature under air with milling time less than 60 min. [ABSTRACT FROM AUTHOR]