Use In Thermoelectric Devices Research Articles

Crystal structure, stability, and transport properties of Li2BeAl and Li2BeGa Heusler alloys: a DFT study

In this study, the structural, elastic, electronic, and thermoelectric properties of full Li2BeAl and Li2BeGa Heusler alloys were explored using density functional and the Boltzmann transport theories. The GGA and HSE approximations have been used for the exchange–correlation potential. Results indicated that these two compounds are more energetically stable in the inverse Heusler structure. Additionally, both Li2BeAl and Li2BeGa Heusler alloys were found to be mechanically stable due to the positive values of the elastic constants. Also, the high values of the Young's modulus indicate that these compounds are stiff and exhibit a semi-metallic nature. The band gaps were determined to be 0.13 eV and − 0.22 eV for Li2BeAl and Li2BeGa alloys, respectively, using the GGA approximation. By employing the HSE hybrid functional, however, the band gap for Li2BeAl increased to 0.26 eV, and for Li2BeGa, it decreased to − 0.16 eV. Regarding thermoelectric properties, Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivities, power factor, and the figure of merit have been calculated for both Li2BeAl and Li2BeGa Heusler alloys at different temperatures. Seebeck coefficient in both alloys decreases with increasing the temperature and has the highest value at 300 K. Thermal conductivity and electrical conductivity increase with increasing the temperature, which confirms the intermetallic behavior of the Heusler alloys. The results obtained for both alloys show that n-type doping has better thermoelectric properties than p-type doping. The maximum value of the figure of merit (ZT) was obtained for n-type doping, which was 1.43 at 660 K for Li2BeAl and 0.39 at 1000 K for Li2BeGa alloy. The high values of ZT especially for electron-dopped Li2BeAl suggest the great potential of this material for use in thermoelectric devices. This study suggests that the proposed materials have potential applications in spintronic devices and thermoelectric materials due to their intermetallic character and effective thermoelectric coefficients.

Fabrication of Metal Contacts on Silicon Nanopillars: The Role of Surface Termination and Defectivity.

The application of nanotechnology in developing novel thermoelectric materials has yielded remarkable advancements in material efficiency. In many instances, dimensional constraints have resulted in a beneficial decoupling of thermal conductivity and power factor, leading to large increases in the achievable thermoelectric figure of merit (ZT). For instance, the ZT of silicon increases by nearly two orders of magnitude when transitioning from bulk single crystals to nanowires. Metal-assisted chemical etching offers a viable, low-cost route for preparing silicon nanopillars for use in thermoelectric devices. The aim of this paper is to review strategies for obtaining high-density forests of Si nanopillars and achieving high-quality contacts on them. We will discuss how electroplating can be used for this aim. As an alternative, nanopillars can be embedded into appropriate electrical and thermal insulators, with contacts made by metal evaporation on uncapped nanopillar tips. In both cases, it will be shown how achieving control over surface termination and defectivity is of paramount importance, demonstrating how a judicious control of defectivity enhances contact quality.

A DFT approach to correlate the physical characteristics of novel chalcopyrites ASbN2(A = Li, Na) for green technology.

Semiconductor chalcopyrite compounds have been a subject of research interest due to their diverse range of physical properties that have captured the attention of scientists. In this ongoing research, we have examined the physical characteristics of LiSbN2 and NaSbN2 chalcopyrites using DFT. The modified Becke-Johnson (mBJ) potential is utilized for the computation of electronic structures. The stability is attained with negative formation energies and optimization curves. A bandgap of 2.60 eV in LiSbN2 and 3.15 eV in NaSbN2 has been achieved, which is further endorsed by the density of states. An in-depth analysis of the optical properties unveils the potential utility of LiSbN2 and NaSbN2 in various photovoltaic devices, attributed to its pronounced absorption in the UV spectrum. The transport characteristics are also assessed through various transport characteristics. The large electrical conductivity and ZT values for both chalcopyrite compounds are attained. Due to their remarkable capability to convert heat into electricity, these materials display potential for use in thermoelectric devices.

Modeling and simulation of multifaceted properties of X2NaIO6 (X = Ca and Sr) double perovskite oxides for advanced technological applications.

In this study, the authors have investigated the structural, optoelectronic, thermoelectric, and thermodynamic properties of Ca2NaIO6 and Sr2NaIO6 double perovskite oxides. Both materials exhibit semiconductor behavior with direct band gaps (Eg) of 0.353eV and 0.263eV, respectively. Optical parameters like absorption coefficient α(ω), reflectivity R(ω), dielectric constants, and refractive index have been calculated. The most notable absorption peaks are identified at 5.52eV (equal to 108.33 × 104cm-1) in the case of Ca2NaIO6 and at 11.16eV (equivalent to 118.17 × 104cm-1) for Sr2NaIO6. These findings suggest a promising outlook for applications in optoelectronics. Moreover, their commendably low thermal conductivity and a high figure of merit, particularly at low temperatures (100K), indicate their effectiveness as thermoelectric materials. This analysis underscores that these materials hold potential as suitable candidates for n-type doping, making them well-suited for use in thermoelectric devices. Studying thermal properties, including thermal expansion, bulk modulus, acoustic Debye temperature, entropy, and heat capacity, contributes to understanding the materials' thermodynamic stability. The titled materials are dynamically stable. The analysis of these double perovskite materials highlights their potential across various technological applications due to their advantageous structural, electronic, optical, and transport properties, offering new possibilities in material science and technology development. The study utilized the full potential linearized augmented plane wave (FP-LAPW) method in conjunction with density functional theory within the WIEN2k simulation code. This approach is widely recognized as one of the most dependable methods for evaluating the photovoltaic characteristics of semiconducting perovskites. The thermoelectric properties were ascertained using the rigid band approach and the constant scattering time approximation, both implemented in the BoltzTraP computational code.

First-principles study of the optoelectronic and thermoelectric properties of lead-free ASnI3 (A = K, Rb, and Cs) novel halide perovskites

In this work, we investigated the optoelectronic and thermoelectric properties of novel lead-free ASnI3 (A = K, Rb, and Cs) perovskite materials employing density functional theory calculations with the most accurate modified TB-mBJ potential. The three studied materials are similar in terms of their computed band profiles. The presence of an energy bandgap between the valence and conduction bands confirms the materials to be semiconductors with an indirect band-type nature. The CsSnI3 with a small gap value compared to the other two materials follows that it would require less energy for excitation. The calculated density of states and their actual electronic orbital contributions are also examined. The projected total density of states shows a successive variation along the energy value. Moreover, the linear optical characteristics are computed and investigated for their possible use in optoelectronic devices. The polarizability of KSnI3 is higher than the other two materials. The studied materials can be potential as an anti-reflecting coating material against UV rays as confirmed by the sharp peaks in the reflectivity spectra. The positive value of RH was consistent with the p-type nature of these materials as also revealed by the Seebeck coefficient and electronic characteristics. The materials seem to be prospective for use in thermoelectric devices supported by the predicted thermoelectric parameters.

Ways of adapting motor transport for the transportation of cargoes in low temperatures

The efficiency of motor transport is largely determined by regional natural and climatic conditions. The main direction of economic activity in Amur region is the production of agricultural products, and the important natural and climatic factors significantly affecting the operation of motor transport are the state of the traffic surface, terrain relief and ambient temperature. In winter, when transporting the finished products, the temperature drops to −35 ... −45 degrees Celsius in some areas, which also imposes certain difficulties in the operation of motor transport. In this regard, in order to improve the efficiency of power resources in these conditions it is necessary to further adapt them to the conditions of use. The proposed article considers the issue of increasing the efficiency of power resources when they are operated at low temperatures through the use of thermoelectric devices, allowing, through the use of secondary energy sources, to improve the performance of the hydraulic system and electrical equipment of a motor vehicle.

A Solvothermal Synthetic Environmental Design for High‐Performance SnSe‐Based Thermoelectric Materials

AbstractSnSe is challenging to use in thermoelectric devices due to difficulties in simultaneously optimizing its thermoelectric and mechanical properties. Here, the authors show a unique solvothermal synthetic environmental design to fabricate super‐large and micro/nanoporous Sn0.965Se microplates by using CrCl3. Cl− ions to trigger Sn‐vacancy formation and optimize the hole concentration to ≈3 × 1019 cm−3, while the as‐formed Cr(OH)3 colloidal precipitations act as “templates” to achieve micro/nanoporous features, leading to low lattice thermal conductivity of ≈0.2 W m−1 K−1 in the as‐sintered polycrystal, contributing to a high ZT of ≈2.4 at 823 K and an average ZT of ≈1.1. Of particular note, the polycrystal exhibits high hardness (≈2.26 GPa) and compression strength (≈109 MPa), strengthened by grain refinement and vacancy‐induced lattice distortions and dislocations; while a single‐leg device provides a stable output power (>100 mW) and conversion efficiency of ≈10% by a temperature difference of 425 K, indicating great potential for applying to practical thermoelectric devices.

Rhodium-based half-Heusler alloys as thermoelectric materials.

Thermoelectric phenomena provide an alternative for power generation and refrigeration, which could be the best solution to the energy crisis by utilizing waste heat energy in the near future. In this study, we have investigated the structural, elastic, electronic, and thermoelectric properties of 18-valence electron count rhodium-based half-Heusler alloys focusing on RhTiP, RhTiAs, RhTiSb, and RhTiBi. The non-existence of imaginary frequencies in the phonon dispersion curve for these systems verifies that they are structurally stable. RhTiP is ductile, while others are brittle. The alloys are semiconducting with indirect band gaps ranging from 0.94 to 1.01 eV. While considering thermoelectricity, we discovered that p-type doping is more favorable in improving the thermoelectric properties. The calculated power factor values with p-type doping are comparable to some of the reported half-Heusler materials. The optimum figure of merit ZT is ∼1 for RhTiBi, and in between ∼(0.38-0.67) for RhTiP, RhTiAs, and RhTiSb. The low thermal conductivities and sufficiently large value of power factor of these alloys suggest that they are promising thermoelectric materials for use in thermoelectric applications.

Numerical simulation to evaluate the influence of geometric parameters on the physical behavior of heat exchangers

In the present investigation, a methodology was developed by means of numerical simulation for the evaluation of the influence of the geometric parameters of the heat exchangers used in thermoelectric generation devices. The validation of the proposed methodology was carried out through experimental tests on a diesel engine test bench under four load conditions (2 Nm, 4 Nm, 6 Nm, and 8 Nm) and a constant speed of 3600 rpm. The results obtained show that the methodology proposed by means of the numerical simulation presents a high concordance with the behavior described experimentally. The deviation between the simulation predictions and the experimental results was less than 4%. Additionally, it was evidenced that the change in the geometry of the heat exchanger has a considerable impact on the parameters of heat flow and surface temperature. It was shown that a 50% reduction in fin distance causes an increase of 2% and 2.4% in the previous parameters. Through geometric modifications, the electrical power generated increased by 7.9%. In general, the methodology developed through numerical simulation allows the analysis of the physical, thermal, and hydraulic phenomena present in heat exchangers focused on use in thermoelectric devices.

Preparation of highly efficient thermoelectric Bi-doped Mg2Si0.55-xSn0.4Gex (x = 0 and 0.05) materials with a scalable mechanical alloying method

Mg2Si-type compounds are highly promising materials for use in thermoelectric devices for waste heat energy harvesting. These compounds have great potential because they exhibit high thermoelectric performance, but the scalability of their synthesis is a major issue for applications. In this study, Bi-doped Mg2Si0.55-xSn0.4Gex (x = 0 and 0.05) materials were prepared by mechanical alloying combined with hot press sintering in order to increase the mass capabilities of their synthetic route compared with the typical solid state reaction. The optimum thermoelectric properties were achieved for the best Mg2Si0.57Sn0.4Bi0.03 and Mg2Si0.53Sn0.4Ge0.05Bi0.02 compositions by ball milling for 32 h and the maximum figure of merit (ZT) values were 1.07 and 1.2, respectively.

Experimental investigation and performance assessment of a solar-driven thermoelectric unit for localized heating and cooling applications

Heating, ventilation, and air conditioning systems help maintain the appropriate level of thermal comfort and air quality in buildings. To this end, the energy supply of these systems must be guaranteed. However, continuous efforts are required to improve the energy efficiency of this system and reduce greenhouse gas emissions. In the zero-emission building approach, the use of thermoelectric devices has been proposed to meet the heating/cooling needs in the building and help in flexibly changing the operating conditions according to the user's needs. In this study, an experimental setup was developed consisting of a multipurpose thermoelectric system that is directly powered by a solar photovoltaic panel. The heating mode was designed for space heating, whereas the cooling mode was tailored to an adiabatic box that could cool food and beverages. The results of this study will facilitate the practical use of this device in the future by directly connecting the thermoelectric system to the room and evaluating the response of the system to temperature changes requested by the user. This system has a high potential for delivering heating and cooling loads, achieving a coefficient of performance of 1.6 in the heating mode and 0.8–1.1 in the cooling mode. These results are promising given the current need to reduce negative environmental impacts in the building sector yet maintaining the same level of thermal comfort.

Anti-oxidation characteristics of Silicon Carbide coating layer for skutterudite thermoelectric modules

Skutterudite (SKD) based thermoelectric materials are promising candidates for use in thermoelectric devices at intermediate temperatures (300–600 °C) for waste heat recovery applications, owing to their high dimensionless figure of merit and power factor. However, these materials are reported to exhibit pesting-like oxidation; therefore, it is necessary to develop protective coating technologies at device level to suppress the oxidation of SKD materials for terrestrial power generation applications. Several coating layers including Al2O3, MgO, and SiC were investigated to enhance the durability of SKD materials upon exposure to air. The SiC coating layer effectively prevents oxygen diffusion into the SKD even after thermal aging in air at 450 °C for 10 h. Further, the SiC coating layer was tightly bonded to the SKD without forming an intermetallic compound with SKD. To verify the performance change of SKD after thermal aging, an SKD uni-couple was fabricated and its internal resistance and open-circuit voltage were measured. The obtained thermoelectric parameters demonstrated that the SiC coating layer could prevent the performance degradation of SKD due to oxygen diffusion.

Electronic, Band Offset, and Thermoelectric Properties of ZnO/GaN Heterostructure from First-Principles Study

Structural, electronic, band offset, and thermoelectric properties of zinc oxide (ZnO), gallium nitride (GaN), and the ZnO/GaN heterostructure have been investigated. First, first-principles calculations are used to study the electronic structure of ZnO, GaN, and ZnO/GaN. The band offsets at the ZnO/GaN(0001) heterointerface are then calculated, revealing type II band alignment. The thermoelectric properties of ZnO, GaN, and the ZnO/GaN heterostructure are also studied using Boltzmann transport theory. Moreover, the Seebeck coefficient, electrical conductivity, electrical thermal conductivity, and figure of merit of ZnO, GaN, and ZnO/GaN are calculated. The ZnO/GaN heterostructure exhibits substantially improved thermoelectric properties, suggesting its potential use in thermoelectric devices.

Enhanced thermoelectric performance in polycrystalline N-type Pr-doped SnSe by hot forging

SnSe has attracted significant attention for use in thermoelectric devices due to its reported ultrahigh figure-of-merit ZT in both p- and n-type single crystals, which inspired us to explore the thermoelectric properties of SnSe polycrystals for potential large-scale applications. Here, n-type Sn1-xPrxSe polycrystals are prepared by ball milling and hot pressing. A maximum ZT value of ~0.7 at 773 K is achieved in Sn0.97Pr0.03Se due to the enhanced electron concentration and electrical conductivity resulting from Pr doping at the Sn site. Through hot forging for a higher degree of orientation, a lowered thermal conductivity is obtained along the hot-pressing direction, contributing to an enhanced ZT value of ~0.9 at 773 K in this direction. This study paves a new way for optimization of n-type SnSe by cation-site lanthanide doping.

ANALYSIS OF THE USE OF RENEWABLE ENERGIES IN COLOMBIA AND THE POTENTIAL APPLICATION OF THERMOELECTRIC DEVICES FOR ENERGY RECOVERY

This study investigates the current situation of electricity generation from non-conventional renewable energy sources in Colombia (NCRES). In general, it was shown that Colombia has potential in renewable sources such as solar, wind, and biomass. However, barriers such as lack of human capital, policies focused on conventional technologies and high investment costs have impeded their growth. Although the development of these sources has been encouraged through Law 1715 of 2014, more policies and developments are needed to promote this type of NCRES. The use of thermoelectric devices (TED) can become a potential NCRES alternative, while the political and technological conditions improve in Colombia. Around the world, TEDs have allowed the recovery of waste heat in a variety of industrial applications and the automotive sector. They are allowing in the latter, not only the generation of electric power, but also the reduction in engine emissions. Besides, its characteristics have allowed it to be used for the generation of electric power, both in developed and developing countries. In this document, an example presentation is developed that demonstrates the applications of the TED in the cases above to demonstrate the potential that the TED can have in almost any place that has a heat source. Keywords: Electricity Generation, Energy Policy, Energy Recovery, Non-conventional Renewable Energy, Thermoelectric Device JEL Classifications: L78, L90, O31, Q20 DOI: https://doi.org/10.32479/ijeep.8038

Ti doping effects on the Seebeck coefficient and electrical conductivity of mesoporous ZnO thin film

The low thermal conductivity of mesoporous structures, due to the pores acting as phonon scattering centers, allows their use in thermoelectric devices. However, high Seebeck coefficient and electrical conductivity and low thermal conductivity are required to enhance their thermoelectric properties. In this study, Ti-doped mesoporous ZnO thin films with various Ti concentrations were fabricated and analyzed. When increasing the Ti dopant concentration up to 1.5 at%, the crystallinity and pore structure of the doped films remained almost unchanged, their porosity and thickness slightly increased, the electrical conductivity was also enhanced due to the increased carrier concentration, and the Seebeck coefficient decreased. These Ti doping-induced increase in electrical conductivity and decrease in Seebeck coefficient led to an increase of almost 1.5 times in the power factor of the mesoporous ZnO thin films.

Cellulose Fiber-Based Hierarchical Porous Bismuth Telluride for High-Performance Flexible and Tailorable Thermoelectrics.

Porous modification is a general approach to endowing the rigid inorganic thermoelectric (TE) materials with considerable flexibility, however, by which the TE performances are severely sacrificed. Thus, there remains an ongoing struggle against the trade-off between TE properties and flexibility. Herein, we develop a novel strategy to combine Bi2Te3 thick film with ubiquitous cellulose fibers (CFs) via an unbalanced magnetron sputtering technique. Owing to the nano-micro hierarchical porous structures and the excellent resistance to crack propagation of the Bi2Te3/CF architectures, the obtained sample with a nominal Bi2Te3 deposition thickness of tens of micrometers exhibits excellent mechanically reliable flexibility, of which the bending deformation radius could be as small as a few millimeters. Furthermore, the Bi2Te3/CF with rational internal resistance and tailorable shapes and dimensions are successfully fabricated for practical use in TE devices. Enhanced Seebeck coefficients are observed in the Bi2Te3/CF as compared to the dense Bi2Te3 films, and the lattice thermal conductivity is remarkably reduced due to the strong phonon scattering effect. As a result, the TE figure of merit, ZT, is achieved as high as ∼0.38 at 473 K, which competes with the best flexible TEs and can be further improved by optimizing the carrier concentrations. We believe this developed technique not only opens up a new window to engineer flexible TE materials for practical applications but also promotes the robust development of the fields, such as paper-based flexible electronics and thin-film electronics.

Исследование интегральных характеристик охлаждающей системы с термоэлектрическим модулем

Thermoelectric modules (TEM) are devices using which it is possible to implement either thermoelectric cooling due to the Peltier effect or electricity generation due to the Seebeck effect. In the first case, electric energy is directly converted into thermal energy, and in the second case, thermal energy is converted into electricity. Recent advances in the development of new thermoelectric nanostructured materials with characteristics significantly better than those found in bulk ones, prompted an increased interest in cooling and electricity generation through the use of thermoelectric devices. Special engineering design techniques are used in developing thermoelectric systems. However, such techniques only yield successful results for some simple designs. If the design of a thermoelectric device is non-trivial, some approximations have to be applied for the design, which seriously affects the accuracy of the result. The existing engineering methods for calculating the parameters and integral characteristics of TEMs involve a large number of simplifications and shortcomings, due to which the calculated integral characteristics of a TEM can differ significantly from their actual ones. In the field of thermoelectric devices, numerical simulation has to be used to solve various problems, in particular, for studying and evaluating promising designs of thermoelectric devices. The article presents the mathematical model of a cooling system equipped with TEMs. Numerical solution of the conjugate heat transfer equations describing the cooling system operation is obtained. It is shown that the TEM operating parameters are influenced by a number of factors that should preferably be taken into account in temperature distribution calculations. It is also shown that under real conditions the integral TEM operation parameters may differ considerably from those calculated according to the standard engineering procedures. Owing to its containing a rigorous body of mathematics, the developed model makes it possible to calculate the TEM parameters and integral characteristics under the real conditions of their operation.

Superstrengthening Bi_{2}Te_{3} through Nanotwinning.

Bismuth telluride (Bi_{2}Te_{3}) based thermoelectric (TE) materials have been commercialized successfully as solid-state power generators, but their low mechanical strength suggests that these materials may not be reliable for long-term use in TE devices. Here we use density functional theory to show that the ideal shear strength of Bi_{2}Te_{3} can be significantly enhanced up to 215% by imposing nanoscale twins. We reveal that the origin of the low strength in single crystalline Bi_{2}Te_{3} is the weak van der Waals interaction between the Te1 coupling two Te1─Bi─Te2─Bi─Te1 five-layer quint substructures. However, we demonstrate here a surprising result that forming twin boundaries between the Te1 atoms of adjacent quints greatly strengthens the interaction between them, leading to a tripling of the ideal shear strength in nanotwinned Bi_{2}Te_{3} (0.6GPa) compared to that in the single crystalline material (0.19GPa). This grain boundary engineering strategy opens a new pathway for designing robust Bi_{2}Te_{3} TE semiconductors for high-performance TE devices.

CeB6 thin films produced on different substrates by electron-beam deposition

Films of cerium hexaboride, a material promising for use in thermoelectric devices at liquidhelium temperatures, are produced by electron-beam deposition. Deposition is carried out from ceramic targets onto insulator, semiconductor, and metal substrates at different temperatures. The microstructure, the elemental and phase compositions, the temperature dependences of the resistivity and the Seebeck coefficient are thoroughly studied. CaB6-structured films, for which the structure is characteristic of cerium hexaboride and the elemental composition is close to the stoichiometric composition, are obtained. At low temperatures, the resistivity of the films is somewhat higher than that of single-crystal samples, and the Seebeck coefficient is close to the corresponding coefficient for single-crystal samples. The main cause of the difference between the resistance values is a high concentration of oxygen impurity detected in the films.