Investigation of GaBi1-xSbx based highly mismatched alloys: Potential thermoelectric materials for renewable energy devices and applications

Composition-induced influence on the electronic band structure, optical and thermoelectric coefficients of the highly mismatched GaNSb alloy over the entire range: A DFT analysis

Germanium mono-chalcogenides have received considerable attention for being a promising replacement for the relatively toxic and expensive chalcogenides in renewable and sustainable energy applications. In this paper, we explore the potential of the recently discovered novel cubic structured (π-phase) GeS and GeSe for thermoelectric applications in the framework of density functional theory coupled with Boltzmann transport theory. To examine the modifications in their physical properties, the across composition alloying of π-GeS and π-GeSe (such as π-GeS1-xSex for x =0, 0.25, 0.50, 0.75, and 1) has been performed that has shown important effects on the electronic band structures and effective masses of charge carriers. An increase in Se composition in π-GeS1-xSex has induced a downward shift in their conduction bands, resulting in the narrowing of their energy band gaps. The thermoelectric coefficients of π-GeS1-xSex have been accordingly influenced by the evolution of the electronic band structures and effective masses of charge carriers. π-GeS1-xSex features sufficiently larger values of Seebeck coefficients, power factors and figures of merit (ZTs), which experience further improvement with an increase in temperature, revealing their potential for high-temperature applications. The calculated results show that ZT values equivalent to unity can be achieved for π-GeS1-xSex at appropriate n-type doping levels. Our calculations for the formation enthalpies indicate that a π-GeS1-xSex alloying system is energetically stable and could be synthesized experimentally. These intriguing characteristics make π-GeS1-xSex a promising candidate for futuristic thermoelectric applications in energy harvesting devices.

Exploring thermoelectric materials for renewable energy applications: The case of highly mismatched alloys based on AlBi1-xSbx and InBi1-xSbx

Thermoelectric materials with crystal-amorphicity duality induced by large atomic size mismatch

GeTe Thermoelectrics

Recent Advances in Molecular Design of Organic Thermoelectric Materials

Thermoelectric (TE) materials are an important class of energy materials that can directly convert thermal energy into electrical energy. Screening high-performance thermoelectric materials and improving their TE properties are important goals of TE materials research. Based on the objective relationship among the molar Gibbs free energy (Gm), the chemical potential, the Fermi level, the electronegativity (X) and the TE property of a material, a new method for screening TE materials with high throughput is proposed. This method requires no experiments and no first principle or Ab initio calculation. It only needs to find or calculate the molar Gibbs free energy and electronegativity of the material. Here, by calculating a variety of typical and atypical TE materials, it is found that the molar Gibbs free energy of Bi2Te3 and Sb2Te3 from 298 to 600 K (Gm = -130.20~-248.82 kJ/mol) and the electronegativity of Bi2Te3 and Sb2Te3 and PbTe (X = 1.80~2.21) can be used as criteria to judge the potential of materials to become high-performance TE materials. For good TE compounds, Gm and X are required to meet the corresponding standards at the same time. By taking Gm = -130.20~-248.82 kJ/mol and X = 1.80~2.21 as screening criteria for high performance TE materials, it is found that the Gm and X of all 15 typical TE materials and 9 widely studied TE materials meet the requirement very well, except for the X of Mg2Si, and 64 pure substances are screened as potential TE materials from 102 atypical TE materials. In addition, with reference to their electronegativity, 44 pure substances are selected directly from a thermochemical data book as potential high-performance TE materials. A particular finding is that several carbides, such as Be2C, CaC2, BaC2, SmC2, TaC and NbC, may have certain TE properties. Because the Gm and X of pure substances can be easily found in thermochemical data books and calculated using the X of pure elements, respectively, the Gm and X of materials can be used as good high-throughput screening criteria for predicting TE properties.

Investigation of mechanical, lattice dynamical, electronic and thermoelectric properties of half Heusler chalcogenides: A DFT study

<p indent="0mm">Traditional fossil fuels, which are finite and have high thermal losses, necessitate the development of new energy materials for waste heat recovery. As the world continues to grapple with energy shortages and environmental concerns, finding sustainable and efficient energy solutions has become a priority. Among these solutions, thermoelectric materials have gained significant attention over the past few decades due to their unique properties. These materials stand out because of their modularity and noiseless operation, making them promising candidates for power generation and refrigeration. The efficiency of thermoelectric materials is primarily determined by the dimensionless figure of merit (<italic>ZT</italic>), which is a measure of a material’s ability to convert heat into electricity. <italic>ZT</italic> depends on three key parameters: The Seebeck coefficient, electrical conductivity, and thermal conductivity. Achieving high <italic>ZT</italic> values is essential for the practical application of thermoelectric materials. High <italic>ZT</italic> values require materials that exhibit both low thermal conductivity and high electrical conductivity. However, this is a challenging issue to achieve. Metals, which typically have high electrical conductivity, also have high thermal conductivity, making them less efficient for thermoelectric applications. On the other hand, ceramics, which have low thermal conductivity, generally suffer from poor electrical performance. In the search for ideal thermoelectric materials, researchers have turned their attention to elements that are abundant in the Earth’s crust, such as tin (Sn) and selenium (Se). These elements not only are plentiful but also exhibit properties that are conducive to thermoelectric applications. One compound that has been extensively studied is tin selenide (SnSe). SnSe has garnered interest due to its remarkable thermoelectric performance, particularly in its p-type semiconductor form. It has been reported to have a high <italic>ZT</italic> value of 2.6 at <sc>923 K,</sc> making it one of the most promising thermoelectric materials discovered to date. In addition to SnSe, tin diselenide (SnSe₂) is an n-type semiconductor that has shown potential for thermoelectric applications. Recent research indicates that SnSe₂ has achieved <italic>ZT</italic> values of up to 0.8. Moreover, the combination of SnSe and SnSe₂ in the form of SnSe-SnSe₂ composites has been explored as a way to optimize thermoelectric performance. These composites leverage the advantages of both materials, achieving lower thermal conductivity and enhanced electrical transport properties. Another compound that has emerged as a potential thermoelectric material is Sn₂Se₃, which consists of a 1:1 ratio of SnSe and SnSe₂. Both computational and experimental studies suggest that Sn₂Se₃ is a unique phase distinct from a simple mixture of SnSe and SnSe₂. The band structure and thermoelectric properties of Sn₂Se₃ have been analyzed, revealing potential <italic>ZT</italic> values of around 1.0 for both three-dimensional (3D) and one-dimensional (1D) forms. These findings indicate that Sn₂Se₃ could be a valuable addition to the family of thermoelectric materials. Furthermore, researchers investigated the effects of doping Sn₂Se₃ with elements such as titanium (Ti) and aluminum (Al) to enhance its properties. Doping can improve the stability and electrical resistance of Sn₂Se₃, making it more suitable for practical applications. Relative research has shown that Ti and Al doping can enhance the phase change properties of Sn₂Se₃, potentially leading to higher performance and greater stability. Despite the significant progress made in the development of Sn<italic>_x</italic>Se<italic>_y</italic> compounds for thermoelectric applications, several challenges remain. One of the primary challenges is the synthesis of these materials with consistent properties. Ensuring the stability of the materials is also crucial. Future research should focus on addressing these challenges to unlock the full potential of Sn₂Se₃ and other Sn<italic>_x</italic>Se<italic>_y</italic> compounds as low-cost, high-performance thermoelectric materials.

Pursuit of thermoelectric properties in L21 structured Co2PAl (P = Ru, Rh) ductile ferromagnetic materials: A first principles prospective

The growing demand for efficient waste heat recovery has intensified the search for high-performance thermoelectric (TE) materials with a figure of merit (ZT) above 2.5. In this study, first-principles calculations based on DFT combined with Boltzmann transport theory were employed to investigate the structural, electronic, thermal, and thermoelectric properties of synthesized Mg 3 NF 3 and newly predicted halide perovskites X 3 NI 3 (X = Sr, Ba). Structural stability was verified through geometric optimization, negative formation energies, elastic constants, and phonon dispersion analyses. The band gaps corresponding to Mg 3 NF 3 , Sr 3 NI 3 , and Ba 3 NI 3 were estimated to be 6.811, 1.279, and 0.807 eV (HSE06), respectively, which are insulating and semiconducting, respectively. In contrast, Sr 3 NI 3 and Ba 3 NI 3 show remarkably low thermal conductivities (0.43 and 0.45 Wm −1 K −1 , respectively) combined with large Seebeck coefficients (123.89 and 135.10 μV/K), yielding promising ZT values of 2.5 and 2.6 at 1000 K. The combination of mechanical robustness, thermal stability, and excellent thermoelectric performance positions Ba 3 NI 3 and Sr 3 NI 3 as promising candidates for high-temperature thermoelectric applications. In contrast, Mg 3 NF 3 , despite its modest ZT value, exhibits a high Debye temperature and melting point, indicating strong resistance to thermal degradation and suitability for high-temperature environments.

Layered materials have several properties that make them suitable as high-performance thermoelectric materials. In this study, we focus on the complex metal nitrides SrZrN2 and SrHfN2, which have an α-NaFeO2 layered crystal structure. To determine their electronic band structure features and potential thermoelectric transport properties, we calculated the electronic band structures and electronic transport coefficients for SrZrN2 and SrHfN2 using density-functional theory and Boltzmann transport theory, respectively. Despite the layered crystal structure, SrZrN2 and SrHfN2 both had three-dimensional electronic structures and isotropic electronic transport because of the contribution of the Sr 4d(x(2)-y(2)) + 4d(xy) orbitals to the bottom of the conduction bands in addition to that of the Zr 4d(z)(2) (Hf 5d(z)(2)) orbital. The three-dimensional electronic structures predict the appearance of large Seebeck coefficients (-145 μV K(-1) at 300 K, -370 μV K(-1) at 1200 K) and large electronic thermoelectric figures of merit.

The IV-VI compound SnSe is an environmentally friendly and high-performance thermoelectric material with intrinsically low lattice thermal conductivity. Recent research efforts have focused on enhancing carrier concentration and effective mass to improve power factors, thereby achieving superior thermoelectric performance as reflected in the figure of merit ZT. In context of the anisotropic crystal structure of SnSe, this study utilized a hydrothermal method to synthesize Rb-doped SnSe nanosheets. Rb acts as an acceptor dopant, increasing the hole concentration to 2.0 × 1019 cm-3 and promoting second valence band participation in transport at room temperature, significantly elevating the ZT value of polycrystalline SnSe to 1.41 at 773 K. Furthermore, texture engineering was implemented through a secondary sintering process. This approach facilitates the organized stacking of grains with highly preferred orientations, resulting in a notable improvement of hole mobility perpendicular to the pressure direction to further increase the power factor. By synergistically combining carrier concentration optimization with texture engineering strategies, an exceptional ZT value of 1.74 at 773 K was achieved in polycrystalline SnSe. This work presents a cost-effective, straightforward, and low-temperature synthesis route for the large-scale production of high-performance SnSe thermoelectric materials, offering significant potential for practical applications in energy harvesting and conversion.

Fossil fuel depletion and environmental issues have led to intense study on fuel source, energy efficiency, and associated environmental impact. Alternative energy that is sustainable and environmentally friendly are the most sought-after remedy to avoid further environment deterioration. Thermoelectric (TE) materials have drawn researchers’ attention in recent decades for use as an alternative green energy source, due to their ability of harvesting ubiquitous waste heat using solid-state module that translated into silent during operations with zero-maintenance. However, TE material are uncommon as house-hold power generation because of their low efficiency at low-grade temperature range. This thesis aims at synthesizing TE materials operating at low-grade temperature range using bottom-up strategy, demonstrating improved figures of merit, ZT through composite material. Four main categories of materials were studied, namely: fully inorganic, inorganic nanocomposite, all-polymer, and hybrid polymer composite. For inorganic material system, modulation doping was employed and produced nanocomposites with two electronic effect, i.e., electron charge injection and electron energy filtering that notoriously affecting thermoelectric performance. These two effects were produced by first matching the carrier type of nanodomains/ nanoinclusions and host matrix, i.e., electron or hole, and followed by matching the work function. Such screening of carrier type and matching of work function were experimentally proven to improve thermoelectric performance. For example, a ~2-fold improvement of ZT in Te (p-type, higher work function)/Ag&lt;sub&gt;2&lt;/sub&gt;Se (n-type) nanocomposite with room temperature ZT=0.79 due to electron filtering effect. On the other hand, a 10% decrease of ZT in Cu (n-type, lower work function)/Ag&lt;sub&gt;2&lt;/sub&gt;Se (n-type) nanocomposite with room temperature ZT=0.50, ascribed to the electron charge injection. For hybrid polymer composite, three critical mechanisms in ZT enhancement were investigated, i.e., phonon scattering, energy dependent scattering, and hole phonon interaction. By matching work function of both inorganic nanoparticles (Cu&lt;sub&gt;12&lt;/sub&gt;Sb&lt;sub&gt;4&lt;/sub&gt;S&lt;sub&gt;13&lt;/sub&gt;) and conducting polymer (PEDOT), a low energy barrier of 0.17 eV was produced. We demonstrated optimized ZT were obtained at around 5 wt.% nanoparticles content, which we attribute to a low hole-phonon interaction, an effective phonon scattering, and mainly to the presence of a proper density of low energy barriers, which selectively scatter low energy carriers. In summary, the approaches outlined in this thesis provide a general strategy with high versatility, simplicity, and precision up to nanoscale to modulate the carrier concentration. The screening of carrier type and matching of work function to engineer electronic effect at electronic band structure near Fermi level was first reported and experimentally proven to improve thermoelectric performance for both inorganic nanocomposite and hybrid polymer composite. Nonetheless, the size of nanoparticles is expected to play substantial role in electrical and thermal conductivity. The summarized approach when combine with the size effect study is expected to provide a complete methodology in producing high-performance thermoelectric composite materials.

Highly mismatched alloys (HMAs) is a class of semiconductor alloys whose constituents are distinctly different in terms of size, ionicity and/or electronegativity. Electronic properties of the alloys deviate significantly from an interpolation scheme based on small deviations from the virtual crystal approximation. Most of the HMAs were only studied in a dilute composition limit. Recent advances in understanding of the semiconductor synthesis processes allowed growth of thin films of HMAs under non-equilibrium conditions. Thus reducing the growth temperature allowed synthesis of group III-N–V HMAs over almost the entire composition range. This paper focuses on the GaNxSb1−x HMA which has been suggested as a potential material for solar water dissociation devices. Here we review our recent work on the synthesis, structural and optical characterization of GaN1−xSbx HMA. Theoretical modeling studies on its electronic structure based on the band anticrossing (BAC) model are also reviewed. In particular we discuss the effects of growth temperature, Ga flux and Sb flux on the incorporation of Sb, film microstructure and optical properties of the alloys. Results obtained from two separate MBE growths are directly compared. Our work demonstrates that a large range of direct bandgap energies from 3.4 eV to below 1.0 eV can be achieved for this alloy grown at low temperature. We show that the electronic band structure of GaN1−xSbx HMA over the entire composition range is well described by a modified BAC model which includes the dependence of the host matrix band edges as well as the BAC model coupling parameters on composition. We emphasize that the modified BAC model of the electronic band structure developed for the full composition of GaNxSb1−x is general and is applicable to any HMA.