Candidate for Magnetic Doping Agent and High-Temperature Thermoelectric Performance Enhancer: Hard Magnetic M-type BaFe12O19 Nanometer Suspension

Electro-Thermo-Magnetic Effect-Induced Large Thermoelectric Performance of Calcium Cobaltite Nanocomposites

As attractive thermoelectric oxides, Ca3Co4O9-based materials have been intensively studied for their applications in recent years. However, their thermoelectric performance is enormously limited due to the contradiction of electrical resistivity and thermal conductivity. Herein, BaFe12O19 nanospheres were introduced into the Ca3Co4O9 matrix. The metallic Ag, ferrites, and matrix phase survived together, and a high density of nanoscale BaFe12O19 precipitation was observed. The reduction of work function could lead to band bending and form an interface potential due to the electro-thermo-magnetic effect contributing to the hole migration. As a result, a huge ZT value of 0.51 for the 8 wt % BaFe12O19/Ca3Co4O9 nanocomposites was obtained at 1073 K, accompanied by a low electrical resistivity of 6.7 mΩ·cm and a high Seebeck coefficient of 217.5 μV/K. In addition, a significant reduction of thermal conductivity (1.11 W/(m·K)) occurred, which was due to the nanoscale ferromagnetic phase effectively scattering the mid- and short-wavelength heat-carrying phonons. The synergistic enhancement of thermoelectric performance confirmed that the electro-thermo-magnetic effect is an effective way to solve the challenging problem of performance deterioration in oxide thermoelectric materials.

Band engineering enhances thermoelectric performance of Ag-doped Sn0.98Se

Ag doping can effectively increase the carrier concentration ofp-type SnSe polycrystalline, thereby enhancing the thermoelectric (TE) performance. However, the key role of the transport valence band in Ag-doped SnSe remains unclear. Particularly, understanding the influence of evaluating the optimal balance between band convergence and carrier mobility on weighted mobility is a primary consideration in designing high-performance TE materials. Here, we strongly confirm through theoretical and experimental evidence that Ag-doped Sn0.98Se can promote the evolution of valence bands and achieve band convergence and density of states distortion. The significantly increased carrier concentration and effective mass result in a dramatic increase in weighted mobility, which favors the achievement of superior power factors. Furthermore, the Debye model reveals the reasons for the evolution of lattice thermal conductivity. Eventually, a superior average power factor and averagezTvalue are obtained in the Ag-doped samples in both directions over the entire test temperature range. This strategy of improving TE performance through band engineering provides an effective way to advance TEs.

Thermal transport across the CoSb3-graphene interface

CoSb₃ shows intrinsically excellent electric transport performance but high thermal conductivity, resulting in low thermoelectric performance. The use of graphene to form heterogeneous interfaces shows great potential for significantly lessening the lattice thermal conductivity (κ_L) in CoSb₃-based composites. Molecular dynamics (MD) simulations are carried out in the present work to study the interfacial thermal conductance across the CoSb₃-graphene interface in the temperature range of 300 K to 800 K. The interfacial thermal conductance exhibits irregular fluctuations with temperature and CoSb₃ length. Furthermore, we explored the effect of graphene layers on the interfacial heat transport of the CoSb₃-graphene system. The results demonstrate that graphene layers affect the interfacial thermal conductance due to the suppression of heat flux in multilayer graphene across the c-axis. The phonon density of states (PDOS) of the CoSb₃-graphene system reveals a decreased low-frequency vibration mode at 0-7 THz and an enhanced high-frequency vibration mode compared with those of CoSb₃, indicating that thermal transport can be effectively suppressed by the addition of graphene.

Energy-Saving Pathways for Thermoelectric Nanomaterial Synthesis: Hydrothermal/Solvothermal, Microwave-Assisted, Solution-Based, and Powder Processing

The pillars of Green Chemistry necessitate the development of new chemical methodologies and processes that can benefit chemical synthesis in terms of energy efficiency, conservation of resources, product selectivity, operational simplicity and, crucially, health, safety, and environmental impact. Implementation of green principles whenever possible can spur the growth of benign scientific technologies by considering environmental, economical, and societal sustainability in parallel. These principles seem especially important in the context of the manufacture of materials for sustainable energy and environmental applications. In this review, the production of energy conversion materials is taken as an exemplar, by examining the recent growth in the energy-efficient synthesis of thermoelectric nanomaterials for use in devices for thermal energy harvesting. Specifically, "soft chemistry" techniques such as solution-based, solvothermal, microwave-assisted, and mechanochemical (ball-milling) methods as viable and sustainable alternatives to processes performed at high temperature and/or pressure are focused. How some of these new approaches are also considered to thermoelectric materials fabrication can influence the properties and performance of the nanomaterials so-produced and the prospects of developing such techniques further.

Research Progress on Preparation Methods of Skutterudites

Thermoelectric material is a new energy material that can realize the direct conversion of thermal energy and electric energy. It has important and wide applications in the fields of the recycling of industrial waste heat and automobile exhaust, efficient refrigeration of the next generation of integrated circuits and full spectrum solar power generation. Skutterudites have attracted much attention because of their excellent electrical trGiovanna Latronicoansport performance in the medium temperature region. In order to obtain skutterudites with excellent properties, it is indispensable to choose an appropriate preparation method. This review summarizes some traditional and advanced preparation methods of skutterudites in recent years. The basic principles of these preparation methods are briefly introduced. Single-phase skutterudites can be successfully obtained by these preparation methods. The study of these preparation methods also provides technical support for the rapid, low-cost and large-scale preparation of high-performance thermoelectric materials.

Impurity Removal Leading to High-Performance CoSb3-Based Skutterudites with Synergistic Carrier Concentration Optimization and Thermal Conductivity Reduction

Thermoelectric properties of CoSb₃-based skutterudites are greatly determined by the removal of detrimental impurities, such as (Fe/Co)Sb₂, (Fe/Co)Sb, and Sb. In this study, we use a facile temperature gradient zone melting (TGZM) method to synthesize high-performance CoSb₃-based skutterudites by impurity removal. After removing metallic or semimetallic impurities (Fe/Co)Sb, (Fe/Co)Sb₂, and Sb, the carrier concentration of TGZM-Ce_0.75Fe₃CoSb₁₂ can be reduced to 1.21 × 10²⁰ cm^-3 and the electronic thermal conductivity dramatically reduced to 0.7 W m^-1 K^-1 at 693 K. Additionally, removing these impurities also effectively reduces the lattice thermal conductivity from 7.2 W m^-1 K^-1 of cast-Ce_0.75Fe₃CoSb₁₂ to 1.02 W m^-1 K^-1 of TGZM-Ce_0.75Fe₃CoSb₁₂ at 693 K. As a consequence, TGZM-Ce_0.75Fe₃CoSb₁₂ approaches a high power factor of 11.7 μW cm^-1 K^-2 and low thermal conductivity of 1.72 W m^-1 K^-1 at 693 K, leading to a peak zT of 0.48 at 693 K, which is 10 times higher than that of cast-Ce_0.75Fe₃CoSb₁₂. This study indicates that our facile TGZM method can effectively synthesize high-performance CoSb₃-based skutterudites by impurity removal and set up a solid foundation for further development.

Recent Progress in Multiphase Thermoelectric Materials

Thermoelectric materials, which directly convert thermal energy to electricity and vice versa, are considered a viable source of renewable energy. However, the enhancement of conversion efficiency in these materials is very challenging. Recently, multiphase thermoelectric materials have presented themselves as the most promising materials to achieve higher thermoelectric efficiencies than single-phase compounds. These materials provide higher degrees of freedom to design new compounds and adopt new approaches to enhance the electronic transport properties of thermoelectric materials. Here, we have summarised the current developments in multiphase thermoelectric materials, exploiting the beneficial effects of secondary phases, and reviewed the principal mechanisms explaining the enhanced conversion efficiency in these materials. This includes energy filtering, modulation doping, phonon scattering, and magnetic effects. This work assists researchers to design new high-performance thermoelectric materials by providing common concepts.

Magnetically enhanced thermoelectrics: a comprehensive review

Thermoelectric (TE) materials have great potential for waste-energyrecycling and solid-state cooling. Their conversion efficiency has attracted huge attention to the development of TE devices, and largely depends on the thermal and electrical transport properties. Magnetically enhanced thermoelectrics open up the possibility of making thermoelectricity a future leader in sustainable energy development and offer an intriguing platform for both fundamental physics and prospective applications. In this review, state-of-the-art TE materials are summarized from the magnetism point of view, via diagrams of the charges, lattices, orbits and spin degrees of freedom. Our fundamental knowledge of magnetically induced TE effects is discussed. The underlying thermo-electro-magnetic merits are discussed in terms of superparamagnetism- and magnetic-transition-enhanced electron scattering, field-dependent magnetoelectric coupling, and the magnon- and phonon-drag Seebeck effects. After these topics, we finally review several thermal-electronic and spin current-induced TE materials, highlight future possible strategies for further improvingZT, and also give a brief outline of ongoing research challenges and open questions in this nascent field.

Synergistic Optimization of Electrical-Thermal-Mechanical Properties of the In-Filled CoSb3 Material by Introducing Bi0.5Sb1.5Te3 Nanoparticles

How to realize the synergistic optimization of electrical-thermal-mechanical properties of thermoelectric materials is a key challenge. Using the Bi_0.5Sb_1.5Te₃ nanoparticle as a mixed agent provides an effective way to address this challenge. Here, Bi_0.5Sb_1.5Te₃/In_0.25Co₄Sb₁₂ nanocomposites with different contents of Bi_0.5Sb_1.5Te₃ nanoparticles were successfully prepared by ultrasonic dispersion combined with spark plasma sintering. Phase and microstructure characterization presented that Te nanoparticles were precipitated from Bi_0.5Sb_1.5Te₃ during the SPS sintering process. Transport measurement results showed that the electrical conductivity was increased due to the increased carrier concentration induced by the charge transfer between Te nanoparticles and the matrix. The Seebeck coefficient was also increased due to the selected electron scattering and increased scattering factor. The lattice thermal conductivity was dramatically suppressed because of the enhanced phonon scattering induced by the Bi_0.5Sb_1.5Te₃ nanoparticles and in situ-precipitated Te nanoparticles and increased dislocations. As a result, a higher average ZT value of 1 was obtained in the range of 300-700 K by the decoupling of the electrical and thermal transport properties for the nanocomposite with 0.1 wt % of Bi_0.5Sb_1.5Te₃ nanometer suspension. Furthermore, the flexural strength, fracture toughness, and hardness of the nanocomposites were also improved significantly. This work demonstrates that using the Bi_0.5Sb_1.5Te₃ nanoparticle as a mixed agent can realize the synergistic optimization of electrical-thermal-mechanical properties of the In-filled CoSb₃ thermoelectric material.