Thermoelectric Properties Of Materials Research Articles

Promising thermoelectric performance in p-type AgBiSe2 doping with alkaline-earth metals

P-type AgBiSe2 is a promising thermoelectric material because of its intrinsic low lattice thermal conductivity and multiple valence band behavior. However, realizing high performance in p-type AgBiSe2 is challenging due to the doping bottleneck. In this work, the enhancement of thermoelectric performance for p-type AgBiSe2 has been successfully realized by adding an excess amount of Se and doping with alkaline-earth metals. We show that Ca or Mg doping at the Bi site effectively increases the room-temperature hole concentration and improves the electrical transport properties of p-type AgBiSe2. Combined with the intrinsic lower thermal conductivity, the maximum zT values of ∼0.74 and ∼0.63 at 448 K were achieved in AgBi0.98Ca0.02Se2 and AgBi0.98Mg0.02Se2, respectively. This work demonstrates a crucial strategy for improving the thermoelectric properties of p-type AgBiSe2-based materials.

Influence of lattice strain on the mechanical properties of CoSb3 skutterudites

Elemental doping has been widely employed to manipulate the electrical and thermal transport properties of thermoelectric materials, without considering the influence to mechanical properties. In skutterudites, electronegative S-dopants have been found to reduce the lattice thermal conductivity. However, the effect of the covalent S-Sb bond on the mechanical properties of CoSb3 skutterudites remains unexplored. Compressive strength, in particular, exhibits a significant reduction in S-doped skutterudites, measuring only 249 MPa, representing a nearly 50% decrease compared to binary skutterudites. Additionally, there is a noticeable drop in the elastic, bulk and shear modulus. With molecular dynamics calculations, the shear strength of S-doped skutterudites also follows a sharp drop at a small ultimate strain. The evolutions of atomic configurations reveal that the lattice strain induced by S-dopants softens the Sb-Sb bond, ultimately leading to structure collapse under low shear stress conditions. These findings underscore the necessity for a comprehensive approach to elemental doping in thermoelectric community.

Advances in flexible inorganic thermoelectrics

AbstractSolid‐state bismuth telluride‐based thermoelectric devices enable the generation of electricity from temperature differences and have been commercially applied in various fields. However, in many scenarios, the surface of the heat source is not flat. Therefore, it is crucial to develop flexible thermoelectric materials and devices to efficiently utilize heat sources and expand their applications. Compared with organic thermoelectric materials and devices, inorganic flexible thermoelectric materials and devices have much higher thermoelectric performance and stability. Considering the rapid development in this research field, we carefully summarize the design principles, structures, and thermoelectric properties of inorganic flexible materials and their devices reported in the recent 3 years, including sulfides, selenides, tellurides, and composite materials designed based on these inorganics. The structural designs of flexible thermoelectric devices based on micro‐sized bulk materials are also carefully summarized. Additionally, we overview the mechanical stability and methods for reducing internal resistance for designs of inorganic flexible thermoelectric devices. In the end, we provide outlooks on future research directions for inorganic flexible thermoelectric materials and devices. This review will help guide thermoelectric researchers, beginners, and students.

Effect of the Spark-Plasma-Sintering Temperature on the Structure, Crystallographic Texture, and Thermoelectric Properties of Materials Based on One-Dimensional Particles of Bi2Te2.7Se0.3

Effect of the Spark-Plasma-Sintering Temperature on the Structure, Crystallographic Texture, and Thermoelectric Properties of Materials Based on One-Dimensional Particles of Bi2Te2.7Se0.3

Numerical analysis of thermoelectric power generation coupled with temperature-dependent material properties

Thermoelectric generator (TEG) with improved performance is a promising technology in power supply and energy harvesting. Existing studies primarily adopt constant material properties to investigate TEG performance. However, thermoelectric (TE) material properties are subjected to considerable variations with temperature. Thus, reasonable doubts have risen concerning the influence level of temperature-dependent material properties on TEG performance. To solve this problem, an efficient and a comprehensive one-dimensional numerical model is developed to fully consider the third-order polynomial temperature-dependent thermal conductivity, Seebeck coefficient, and electrical resistivity. Control volume and finite difference algorithms are compared, and experiments are conducted to verify the developed numerical model. The temperature distribution along the TE leg obviously differs from the parabolic shape, which is a classic temperature distribution under the assumption of constant material properties. Insights find that the local change rate of thermal conductivity and Thomson effect are the essential reasons for the abovementioned phenomenon. It has been found that Thomson heat is released in the part of the leg near the cold-end, whereas it is absorbed in the remaining parts of the leg near the hot-end. The electric power on the basis of constant material properties is confirmed to be accurate enough by the developed numerical model, but the parabolic shape of the TE efficiency can be only obtained when temperature-dependent material properties are considered. Furthermore, it is wise to improve the TE efficiency by structural optimization. The present work provides an efficient and a comprehensive one-dimensional numerical model to include temperature-dependent material properties. New insights into the temperature and heat flux distribution, Thomson influence, and structural optimization potential are also presented for the in-depth understanding of the TE conversion process.

Modulating the thermoelectric transport properties of the novel material Er2Te3 via strain

AbstractThe rare‐earth chalcogenide Er2Te3, characterized by its low lattice thermal conductivity, represents a highly promising and innovative thermoelectric material. However, there have been limited studies exploring its thermoelectric properties in depth. Additionally, it has been discovered that strain engineering is an effective method for enhancing thermoelectric properties, a technique successfully applied to relevant materials. In this study, we employed a first‐principles approach in conjunction with the semi‐classical Boltzmann transport theory to investigate the thermoelectric properties of Er2Te3 materials under −4% to 4% strain. The results indicate that applying compressive strain modulates thermoelectric properties more effectively than tensile strain for Er2Te3. Under strain modulation, the maximum power factor for both p‐type and n‐type Er2Te3 increases significantly, from 0.9 to 2.5 mW m−1 K−2 and from 14 to 18 mW m−1 K−2 at 300 K, respectively. Moreover, the figure of merit (ZT) for p‐type and n‐type Er2Te3 improves notably, from 0.15 to 0.25 and from 1.15 to 1.35, respectively, under −4% strain. Consequently, the thermoelectric properties of Er2Te3 materials can be significantly enhanced through strain application, with n‐type Er2Te3 demonstrating substantial potential as a thermoelectric material.

Close‐packed layer spacing as a practical guideline for structure symmetry manipulation of IV‐VI/I‐V‐VI2 thermoelectrics

AbstractThe crystal‐structure symmetry in real space can be inherited in the reciprocal space, making high‐symmetry materials the top candidates for thermoelectrics due to their potential for significant electronic band degeneracy. A practical indicator that can quantitatively describe structural changes would help facilitate the advanced thermoelectric material design. In face‐centered cubic structures, the spatial environment of the same crystallographic plane family is isotropic, such that the distances between the close‐packed layers can be derived from the atomic distances within the layers. Inspired by this, the relationship between inter‐ and intra‐layer geometric information can be used to compare crystal structures with their desired cubic symmetry. The close‐packed layer spacing was found to be a practical guideline of crystal structure symmetry in IV‐VI chalcogenides and I‐V‐VI2 ternary semiconductors, both of which are historically important thermoelectrics. The continuous structural evolution toward high symmetry can be described by the layer spacing when temperature or/and composition change, which is demonstrated by a series of pristine and alloyed thermoelectric materials in this work. The layer‐spacing‐based guideline provides a quantitative pathway for manipulating crystal structures to improve the electrical and thermal properties of thermoelectric materials.

Enhancement of thermoelectric properties in rapidly synthesised β-Cu2Se using optimized Cu content and microwave hybrid heating

To our knowledge, this is the first study to successfully synthesise high-temperature-phase copper selenide (β-Cu2Se) at room temperature using rapid microwave hybrid heating (MHH). Controlling the starting Cu/Se ratio is the critical parameter for adjusting the content of α- and β-phases in the as-synthesised sample. The relatively low Cu composition causes impurities to form in the Cu3Se2 phase, deteriorating the thermoelectric (TE) properties of the Cu2Se material. The β phase formation at room temperature promotes electrical conductivity. The thermal conductivities of the Cu2.0Se samples were 0.5–0.8 Wm−1K−1 at 303–673 K. A strong electronic-phonon interaction may potentially couple electronic thermal conductivity (κe) and lattice thermal conductivity (κL), resulting in incomplete separability of κL and κe in the β-Cu2.0Se sample. The Cu2.0Se exhibited a ZT value of 0.65 at 523 K because of its considerably lowered thermal conductivity.

Oxygen vacancy-activated thermoelectric properties of ZnO ceramics

Understanding the structural and thermoelectric (TE) properties of a pure material is essential for developing a practical approach to improve its TE performance. This study focuses on the high-temperature TE properties of ZnO ceramics synthesized by the spark plasma sintering (SPS) technique. The analyses of crystallinity and microstructure along with photoluminescence and Raman spectroscopy indicated an increase in oxygen vacancy in the ZnO ceramics with SPS temperature, which resulted in unit-cell shrinkage, lattice modification, grain densification, and TE modification. Specifically, oxygen vacancies were found to be a crucial factor affecting the TE performance of the spark-plasma-sintered ZnO ceramics at temperatures exceeding 773 K. Oxygen vacancies can act as carrier donors when they are ionized, contributing to an increase in electrical conductivity and a decrease in thermal conductivity. Additionally, this study proposes a potential way to engineer native defects in ZnO ceramics by controlling the SPS process.

Effects of introducing MXene on thermoelectric properties of Cu2Se alloys

Nano-second-phase dispersion usually improves the thermoelectric properties of thermoelectric materials through energy filtering effects and phonon scattering effects. In this paper, MXene was introduced as a new nano second phase material into the Cu2Se alloy bulks prepared by the hydrothermal method and the vacuum hot-pressing method. The microstructure, electrical and thermal transport properties of the samples were studied, and the results showed that the introduction of MXene can not only optimize its electrical transport properties, but also significantly suppress its thermal conductivity, thereby effectively improving its thermoelectric properties. Overall, the maximum ZT value of the Cu2Se + 0.20 mol % MXene sample reached 1.77 at 923 K, which was 30 % higher than that of the pristine Cu2Se sample.

Investigating Electronic, Optical, Thermodynamic, and Thermoelectric Properties of SrO and SrO2 Phases: A Density Functional Theory Approach.

The significance of strontium oxide (SrO) and strontium peroxide (SrO2) is currently being investigated as one of the countless potential uses for green energy. However, few studies have examined the distinctive properties of several phases of SrO and SrO2. In order to fill this research gap, we have conducted a study on their various properties through "density functional theory (DFT)" under ideal conditions. This includes the study of electronic, optical, thermodynamic, and thermoelectric properties of the above-mentioned materials. For this study, the "Quantum Espresso" tool in DFT using Perdew-Burke-Ernzerhof-generalized-gradient approximation (PBE-GGA) as the exchange-correlation functional and "Optimized Norm-Conserving Vanderbilt (ONCV)" as the pseudopotential has been used. The face-centered cubic (FCC), body-centered cubic (BCC), hexagonal-1, and hexagonal-2 phases of SrO and the tetragonal and orthorhombic phases of SrO2 have been selected for the aforesaid study, for which some structural information has already been available. During this study, the energy band gap as an electronic property; the dielectric constant, refractive index, absorption coefficient, reflectivity, and energy loss function as optical properties; entropy, heat capacity, Debye temperature, and Debye sound velocity as thermodynamic properties; and the Seebeck coefficient, thermal conductivity, electrical conductivity, and figure of merit as thermoelectric properties have been investigated. In addition, phonon dispersion curves and formation energies have been used to confirm the dynamical stability and thermodynamic stability, respectively, for all of the materials mentioned above. The curve showed that the FCC, hexagonal-1, and hexagonal-2 phases of "SrO" are dynamically stable. These materials have good optoelectronic properties and can be used in ultraviolet sensors due to their intermediate band gap and highest material response in the ultraviolet range. In terms of thermoelectric property, the maximum value of "figure of merit" for the above material has been achieved up to 0.5. Satisfactory agreement has been found between the current findings and the known theoretical and experimental findings.

Structural, optical, elastic, thermoelectric and thermodynamic properties of the IrMn material: A DFT study

In this work, we present a study of the structural, optical, elastic, thermoelectric and thermodynamic properties of iridium manganese (IrMn) using the code “WIEN2k” with the full potential linearized augmented plane wave (FP-LAPW) method. The lattice constants of the IrMn compound are calculated by the generalized gradient approximation with Perdew–Burke–Ernzerhof (GGA-PBE). Indeed, we have studied the magnetism exhibited by the compound IrMn. We found that the antiferromagnetic phase of this material is the most stable phase. The magnetic moment, plasma frequency, bandgap, elastic constants, and electronic and magnetic properties of this material are deduced and discussed. We have shown that the antiferromagnetic phase is the most stable with a minimum energy value of around −1034947.477[Formula: see text]eV. We optimized the [Formula: see text] ratio and found that its value is approximately [Formula: see text] 0.923133. On the other hand, the absorption and reflectivity coefficients, the optical conductivity and the dielectric tensor are studied. In addition, the thermo-electric and thermodynamic properties have been illustrated. The IrMn compound could be useful for different applications of spintronics.

Thermoelectric performance enhancement in Sr0.9La0.1TiO3-based ceramics by high-pressure, high-temperature treatment

As an oxide thermoelectric material, the adjustment of oxygen vacancy plays an important role in strontium titanate (SrTiO3). Traditional synthesis methods typically necessitate post-synthesis reduction annealing to optimize its electrical properties. However, the oxygen vacancy concentration of samples synthesized by this approach may be distributed in a gradient manner. In this study, a high-temperature and high-pressure (HPHT) synthesis treatment was adopted, incorporating titanium powder into the raw material. This novel approach leverages the closed environment created by high pressure and the robust oxygen-trapping capabilities of titanium powder at elevated temperatures. It resulted in enhanced electrical properties in synthesized samples without the need for reduction annealing. Building upon this achievement, we successfully synthesized SrTiO3 samples doped with lanthanum (La) at different pressures. The sample synthesized at 5GPa demonstrated an optimal zT value of 0.22 at 973 K. This work provides a novel approach to the effective synthesis and improved electrical properties of strontium-based thermoelectric materials.

The mechanism of the effect of V doping on the thermoelectric properties of bismuth telluride material

The mechanism of the effect of V doping on the thermoelectric properties of bismuth telluride material

Effect of Composition Adjustment on the Thermoelectric Properties of Mg3Bi2-Based Thermoelectric Materials.

Thermoelectric materials are widely used in refrigeration chips, thermal power generation, catalysis and other fields. Mg3Bi2-based thermoelectric material is one of the most promising thermoelectric materials. Herein, the Mg3Bi2-based samples were prepared by high temperature synthesis, and the influence of Mg/Sb content on the electrical transport properties and semi-conductivity/semi-metallicity of the materials has been studied. The results indicate that the efficiency of introducing electrons from excess Mg prepared by high temperature synthesis is lower than that introduced by ball milling, due to the high vapor pressure of Mg. The doping of Sb/Te at the Bi site would make it easier for the material to change from p-type conduction to n-type conduction. With the increase in Mg content, the semi-conductivity of the material becomes weaker, the semi-metallicity becomes stronger, and the corresponding conductivity increases. With the increase in Sb content, the samples exhibit the opposite changes. The highest power factor of ~1.98 mWm-1K-2 is obtained from the Mg3.55Bi1.27Sb0.7Te0.03 sample.

Towards energy filtering in Mg2X-based composites: Investigating local carrier concentration and band alignment via SEM/EDX and transient Seebeck microprobe analysis

A comprehensive understanding of multi-phase materials requires the characterization of transport properties at the micro/nano-scale. Optimized alignments of the conduction bands and valence bands at the interfaces of multi-phase materials can enhance the properties of thermoelectric materials by filtering out undesired charge carriers and is a promising path towards high performance thermoelectric devices. Here, a micro-scale characterization technique using transient Seebeck microprobe analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and electronic transport modelling based on the Boltzmann transport equation modeling is introduced to assess the band diagram and estimate the band offset in multi-phase materials. This characterization technique is applied to a composite of magnesium silicide-based materials. This material class is prone to form self-assembling nano-structured composites driven by a miscibility gap in the solid solutions series. Our analysis reveals changes in carrier concentration upon composite formation and considerable band offsets for both conduction and valence band when synthesizing nominally undoped composites. Employing Bi as dopant we show that Bi exhibits a preference for the Sn-rich phase, changing the carrier concentration differently in the Sn-rich matrix phase compared to the Si-rich secondary phase, effectively altering the band alignment of the composite. This demonstrates that our approach can be utilized to measure and manipulate the band offset within the composite to achieve optimal thermoelectric performance.

Precise temperature control of electronic devices under ultra-high thermal shock via thermoelectric transient pulse cooling

Thermoelectric transient pulse cooling can break through the limitations of thermoelectric material properties and achieve cooling performance beyond steady-state, which has great potential in active thermal management of high-power electronic devices. However, traditional control strategy for thermoelectric cooler (TEC) under steady cooling modes severely limits the widespread application of pulse cooling. This work focused on the key issue of precise temperature control under ultra-high thermal shock, and developed a novel control strategy composed of PID control, transient pulse control, and feed-forward control. By involving the thermoelectric transient pulse cooling effect, TEC can bear much high thermal load, and feed-forward control can further improve the temperature stability. As a result, the new strategy can bear extreme pulse thermal load as high as 4.59 times of the maximum cooling capacity of the TEC in steady-state within width of 20 ms, and the temperature fluctuation can be suppressed to 0.5 K from 7.58 K by using traditional control strategy based on maximum steady-state cooling capacity. This work demonstrates that the control strategy based on transient pulse cooling can greatly improve the capacity and response speed of thermoelectric cooling, providing important reference for precise temperature control of high-power electronic devices.

A large magnetocaloric effect and thermoelectric properties of anti-perovskite SnMn3N material: a DFT study and monte carlo simulation

In this paper, we have investigated the electronic, magnetic, magnetocaloric, and thermoelectric properties of the anti-perovskite material SnMn3N using density functional theory (DFT) calculations and Monte Carlo simulations. We observed a second-order phase transition at a temperature of T = 480 K. Firstly, we studied the structural and electronic properties of the material. The crystal structure of this material is cubic with a spatial group of Pm3m. Secondly, we examined the magnetocaloric properties of this metallic compound by calculating the magnetic entropy change ) and the relative cooling power (RCP) under different magnetic fields: 1 T, 3 T, and 5 T. The values obtained for these parameters were 19.382 J kg−1 K−1 and 203.466 J kg−1 at an external magnetic field of 5 T, respectively. Lastly, we also analyzed the thermoelectric properties of the compound using the BoltzTraP and Gibbs2 methods. We determined that the Seebeck coefficient at room temperature is 17.7766 μV K−1) and 23.099 μV K−1) in the transition phase at 480 K. We are currently conducting measurements of the thermal conductivity and power factor of this material at both room temperature and the transition temperature of 480 K. In summary, this study provides a deeper understanding of the magnetocaloric, thermoelectric, and thermal properties of the SnMn3N material, which can potentially be utilized in the development of more efficient cooling systems.

First principles study on the thermoelectric properties of GaN nanowires with CN point defects

In this paper, the effects of CN point defects on the thermoelectric properties of GaN nanowires (NWs) were investigated by using first principles calculation. It is found that the CN point defects can increase the electronic density of states (DOS) near the Fermi level of GaN NWs. The calculation results indicate that CN point defects are beneficial for improving the power factor (PF) of GaN NWs. In addition, it was found that CN point defects can increase the electrical conductivity of NWs. At the same time, it also has impact on the thermal conductivity and Seebeck coefficient of NWs. CN point defects will increase the electrical conductivity of GaN NWs from 0.41 × 10 14Wm−1k−1s−1 to 1.15 × 10 14Wm−1k−1s−1 at T = 700 K. In addition, it's also found that as the temperature increases, CN will cause the Seebeck coefficient decreased from 0.001 VK−1 to 0.0008 VK−1 when T = 700 K. It’s useful for further understanding the thermoelectric properties of wide bandgap semiconductor materials and improving the performance of thermoelectric devices.

Thermoelectric Power Factor of Boron‐Doped Carbon Nanotubes Reinforced Cementitious Composites

In recent years, fossil fuel emissions and human activities have generated a lot of heat energy, causing environmental temperatures to rise. Thermoelectric cementitious composites that use temperature difference power generation to achieve the transformation of thermal and electrical energy can achieve a reduction in urban environmental temperature and alleviate resource depletion. However, the low thermoelectric conversion efficiency at this stage restricts its development. Herein, boron‐doped carbon nanotubes (B‐CNTs) are proposed to improve the thermoelectric properties of cement materials by doping boron into carbon nanotubes through the thermal diffusion method. At H3BO3: CNTs = 1:4, the synthesized B‐CNTs improve the Seebeck coefficient, which is mainly due to the increase in defect content and the appearance of additional phases around the Fermi energy level, leading to enhanced thermoelectric properties due to the increase in carrier scattering intensity. The thermoelectric optimum of the cement matrix composite with 7.0 wt% B‐CNTs content is 1.1 × 10−4, which is three times higher than that of the undoped carbon nanotube. This article provides a research idea to modify the thermoelectric properties of the material by doping the carbon material.