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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]

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]

[Display omitted] • Si epitaxial multilayers with embedded CrSi 2 / β-FeSi 2 nanocrystals were grown on Si(1 1 1). • The types and values of CrSi 2 and β-FeSi 2 nanocrystal lattice deformations were defined. • Seebeck coefficient sign change was observed in CrSi 2 (β-FeSi 2)-p/Si-n heterostructure. • The minimum number of holes injected from a single (CrSi 2 /β-FeSi 2) NC was estimated. • Main mechanisms of hole injection from CrSi 2 (β-FeSi 2)-p/Si-n Ncs were established. The possibility of ordered embedding of CrSi 2 and β-FeSi 2 nanocrystals (NCs) into a Si(1 1 1) substrate of n-type conductivity has been demonstrated. The types of NCs and silicon matching were determined, and the types of the crystal lattice deformations of CrSi 2 and β-FeSi 2 NCs were established. For six-layer heterostructures with embedded CrSi 2 and CrSi 2 + β-FeSi 2 NCs, a change in the Seebeck coefficient sign from negative to positive was observed for the first time in a 250–400 K temperature range, which indicates a nanocrystals to silicon hole injection. An estimate was made of the minimum number of holes, injected from a single nanocrystal, which are necessary to compensate for the thermo-emf from an n-type substrate. Band diagrams were constructed for the β-FeSi 2 -p NC/Si-n and CrSi 2 -p NC/Si-n heterojunctions, and the discontinuities in the valence and conduction bands were determined. The minimum barrier (0.065 eV) for holes in the Si-p/NC β-FeSi 2 -p/Si-n system indicates their thermal generation as the main mechanism. The main mechanism of hole injection from Si-p/NC CrSi 2 -p/Si-n system is tunneling through the surface states in the Si band gap due to the large discontinuity (1.075 eV) in the Si valence band. [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]