High-entropy engineering in (Sr,Ba,RE)Nb2O6-δ tungsten bronze oxides: achieving ultralow thermal conductivity and enhanced thermoelectric performance

Fundamental understanding of lattice softening and phonon transport in crystalline solids is crucial for thermoelectric applications, since the design of thermally insulating solids has gained significant interest over the years. In this work, we demonstrate strain induced lattice softening through negative thermal expansion (NTE) in Pr doped BiCuSeO, which breaks the theoretical Cahill limit, κlmin ∼ 0.55 W m−1 K−1, achieving a low κl of 0.24 W m−1 K−1 at 740 K. The Differential Scanning Calorimetry (DSC) and Raman analyses experimentally confirm NTE-driven lattice softening, which influences glass-like thermal transport beyond the theoretical limit. Meanwhile, the negative Gruneisen parameter (−1.13) calculated from reduced average sound velocity, νs∼1870 ms−1, with shrinkage of cell volume illustrates the NTE behavior. Furthermore, the observed weak carrier–phonon coupling μW/κl indicates the absence of conventional carrier scattering through NTE, which leads to a 54% increment in zT compared to undoped BiCuSeO (0.5 at 740 K) for Bi0.97Pr0.03CuSeO.

Armchair graphene nanoribbons (AGNRs) are promising candidates for nanoscale thermoelectric applications due to their tunable bandgap and high electrical conductance. However, their inherently high thermal conductance limits thermoelectric efficiency. In this study, we investigate the effects of vacancy defects and copper (Cu) doping on the thermoelectric performance of AGNRs using the extended Hückel method combined with nonequilibrium Green's function (NEGF) formalism. The results show that the introducing vacancy defects reduces both the bandgap and phononic thermal conductance, thereby creating a favorable platform for thermoelectric enhancement. Low-concentration Cu doping, especially single-atom doping, improves electrical conductance and the Seebeck coefficient, resulting in a peak ZT value exceeding 1.5 at room temperature. The power factor is also significantly improved under optimized doping conditions. In contrast, high doping levels lead to reduced Seebeck coefficients and increased electronic thermal losses, lowering overall efficiency. These findings highlight the importance of precise control over dopant concentration and placement. Overall, this work demonstrates a viable approach for engineering high-performance thermoelectric materials using defect and dopant strategies, supporting future development of low-power, energy-harvesting devices in electrical and electronic systems.

Due to the scarcity of renewable energy sources and the increase in fossil fuel consumption, the development of materials for renewable and sustainable energy production has become an eminent concern, including thermoelectric power generation. Advanced ceramics such as SiC is a desirable alternative material for high-temperature thermoelectric applications. Although SiC has a high Seebeck coefficient, it has relatively low electrical and thermal conductivities, which are undesirable properties for thermoelectric applications. Introducing transitional metal borides as a secondary phase to enhance the electrical conductivity of SiC is a common method. In this study, SiC granules were coated with TiB₂ powders using a simple dry coating method and subsequently subjected to spark plasma sintering to produce composites with conductive network structures. To modify the morphology of the TiB₂ network, SiC granules were classified with particle size ranges of 25-50 µm to 75-100 µm prior to the coating process, Increases of ≈130-500% in electrical conductivity was achieved depending on the matrix granule size distribution, which decreased with increasing SiC granule sizes, showed that the higher concentration of TiB₂ network lowered the percolation threshold causing drastic increases in electrical conductivity. The ZT value increased by ≈50% in the 25-50 µm range.

In this study, a comprehensive first-principles investigation of the structural, elastic, electronic, optical, and thermoelectric properties of the ternary intermetallic compounds HfBeIr2 and TiBeIr2 is presented. The calculations were performed within the framework of density functional theory using the full-potential linearized augmented plane wave method. Structural optimization confirms that both compounds crystallize in a stable cubic Fm-3m phase, with TiBeIr2 exhibiting a reduced lattice parameter and enhanced mechanical rigidity compared to HfBeIr2. The calculated elastic constants satisfy the mechanical stability criteria, indicating that both materials are mechanically stable, stiff, and exhibit slight elastic anisotropy. Electronic band structure and density of states analyses reveal the metallic nature of both compounds, with dominant contributions from transition metal d-orbitals near the Fermi level. Optical properties demonstrate characteristic metallic behavior, including high reflectivity in the infrared and visible regions and strong absorption in the ultraviolet range, suggesting potential applications in optoelectronic and coating technologies. Thermoelectric properties were evaluated using Boltzmann transport theory, revealing a clear contrast between the two compounds. TiBeIr2 exhibits superior thermoelectric performance, with a steadily increasing figure of merit (ZT) reaching ~0.014 at 1000 K, while HfBeIr2 shows negligible efficiency. The enhanced performance of TiBeIr2 is attributed to its favorable balance between electrical conductivity, Seebeck coefficient, and thermal conductivity. These findings highlight TiBeIr2 as a promising candidate for high-temperature thermoelectric applications.

Abstract Materials with intrinsically low lattice thermal conductivity ($\kappa_l$) are highly desirable for high-performance thermoelectric applications. Using first-principles calculations combined with Boltzmann transport theory, we systematically investigate the thermoelectric properties of a family of two-dimensional Janus semiconductors, ${\mathrm{\gamma}}$-$\mathrm{Ge_{2}}XY$ ($X,Y=$ S, Se, Te). All three compounds exhibit ultralow $\kappa_l$ at room temperature, reaching 6.16, 1.16, and 4.91 W/mK for $\mathrm{\gamma}$-$\mathrm{Ge_{2}SSe}$, $\mathrm{\gamma}$-$\mathrm{Ge_{2}STe}$, and $\mathrm{\gamma}$-$\mathrm{Ge_{2}SeTe}$, respectively. Combined with favorable electronic structures featuring enhanced density of states near the band edges, these materials achieve high thermoelectric performance, with maximum $ZT$ values of 2.48–2.59 at 900 K. Notably, biaxial tensile strain further boosts the thermoelectric efficiency of $\mathrm{\gamma}$-$\mathrm{Ge_{2}SeTe}$, yielding an exceptional n-type $ZT$ of 4.78 at 900 K under 2% strain. This remarkable enhancement originates from strain-induced strengthening of lattice anharmonicity and an increased Seebeck coefficient associated with conduction-band modulation. Our results identify Janus $\gamma$-$\mathrm{Ge_{2}}XY$ monolayers as promising platforms for next-generation thermoelectric energy conversion and highlight strain engineering as an effective route for targeted performance optimization.

We present a systematic comparative study of the structural, mechanical, vibrational, electronic, and thermoelectric (TE) properties of layered III-VI semiconductors GaSe, InSe, and TlSe using first-principles density functional theory and phonon transport calculations. Among the three, GaSe exhibits the highest thermodynamic and mechanical stability, whereas InSe displays ductile behavior, and TlSe remains mechanically softer, with lower elastic moduli. This reduced mechanical stiffness in TlSe plays a crucial role in its thermal transport properties, particularly contributing to a significantly lower lattice thermal conductivity. The Seebeck coefficient is relatively higher for GaSe and InSe due to the presence of unconventional band convergence, which enhances the density of states near the Fermi level and thereby improves the thermopower. In contrast, the absence of such convergence in TlSe results in a lower Seebeck coefficient. However, TlSe exhibits superior electrical conductivity, which, together with its ultralow lattice thermal conductivity, compensates for the reduced Seebeck response. TlSe demonstrates the highest TE efficiency, driven primarily by its ultralow lattice thermal conductivity resulting from pronounced phonon softening, flat acoustic phonon branches, and dominant out-of-plane vibrational modes, which enhance phonon-phonon scattering. While the mid-frequency optical phonon group velocities remain comparable across the systems, the differences in are primarily governed by variations in acoustic and low- and high-frequency optical phonon velocities. The TE figure of merit (ZT) calculations further support the superior performance of TlSe, with a maximum ZT value of 2.89 at 600 K, exceeding that of GaSe (1.68) and InSe (1.41) across the temperature range studied. Bader charge analysis, charge density distribution, and Debye temperature calculations further support the superior TE efficiency of TlSe among the studied compounds. These results highlight TlSe as a promising candidate for TE applications compared to GaSe and InSe, where its ultralow thermal conductivity and optimized phonon dynamics effectively compensate for its relatively lower Seebeck coefficient.

The BaCu2Se2 semiconductor compound with earth-abundant elements is currently studied for application in thermoelectrics. The properties of this emerging material, however, are still not well established, while being mostly investigated on powders or pelletized powders. In this work, BaCu2Se2 thin films are prepared, and the chemical space of Ba-rich and Cu-rich compositions is explored. Ba-Cu-Se thin film combinatorial libraries with lateral compositional gradients with [Cu]/([Ba]+[Cu]) (CBC) atomic ratios between 0.15 and 0.98 are synthesized on areas of 12×50 mm2. Using XRF and XRD analysis, composition-resolved phase fractions are determined, which identify the orthorhombic α-BaCu2Se2 as the main phase for CBC between 0.62 and 0.82. Optical measurements reveal for α-BaCu2Se2 a direct bandgap of 1.89 eV and a high absorption coefficient ∼105 cm-1. Surface photovoltage and Seebeck coefficient measurements show p-type conductivity of the films irrespective of composition. Combined Kelvin probe, photoelectron yield, and optical-pump terahertz-probe spectroscopies demonstrate tunability of charge carrier concentrations over several orders of magnitude. The absolute photoluminescence hyperspectral imaging reveals a bright luminescence centered at 1.91 eV and an implied open-circuit voltage of 1.3 eV. Ba-rich conditions are found to be appropriate for the synthesis of films for photovoltaics, while Cu-rich conditions are suitable for the preparation of this material for thermoelectrics.

Suppressing lattice thermal conductivity is essential for high‐performance thermoelectric materials. Here, first‐principles calculations combined with the linearized Boltzmann transport equation and deformation potential theory were used to investigate the thermal transport and thermoelectric behavior of X 2 Se 2 S (X = Bi, As, and Sb). A counterintuitive mass‐dependent trend was identified: despite being the lightest compound, As 2 Se 2 S exhibits the lowest lattice thermal conductivity, reaching 0.443 W m −1 K −1 at 300 K. This behavior can be understood within the complete Slack framework, in which lattice anharmonicity dominates over atomic mass in determining heat transport. Phonon dispersion and anharmonic force‐constant analyses show that strong acoustic‐optical coupling and abundant low‐frequency optical modes in As 2 Se 2 S enhance phonon scattering, whereas Bi 2 Se 2 S retains a clear acoustic‐optical gap and correspondingly higher thermal conductivity. Owing to its ductile mechanical response and favorable electronic structure, p‐type As 2 Se 2 S achieves a maximum ZT of 0.503 at 850 K, while Sb 2 Se 2 S shows promise for n‐type transport. These results clarify the role of anharmonicity in X 2 Se 2 S compounds and highlight their potential for low‐cost medium‐temperature thermoelectric applications.

First principles study of pristine and Mn-doped Cs2SnX6 (X = Cl, Br, I): A multifunctional perspective for optoelectronic and thermoelectric applications

Extensive DFT analysis of Rb2XTlCl6 (X = Al, K) double perovskites: Exploring potential for thermoelectric and optoelectronic applications

Li2CuXF6 (X = Sb, As): A New Family of Ductile Fluorites-types Perovskites for UV Optoelectronics and High-Efficiency Thermoelectric Applications

MXenes have emerged as versatile materials due to their distinct combination of metallic conductivity, hydrophilicity, mechanical flexibility, and tunable surface chemistry. These properties have enabled their application across various fields such as energy storage, catalysis, and biomedical devices, with thermoelectric energy conversion acquiring attention. MXene distinguishes for its exceptional hardness, high melting point, and electrical conductivity, making it a strong candidate for thermoelectric applications, particularly under high temperature factors. This review provides an overview of the latest advances in the thermoelectric performance of MXenes. We discuss strategies such as doping, hetero structure formation, and defect engineering that have been used to improve parameters, including the Seebeck coefficient and to suppress lattice thermal conductivity, thereby improving the figure of merit (ZT). Challenges related to synthesis scalability, material stability, and the undermine between electrical and thermal transport are crucially evaluated. This study emphasizes directions for the future, including the evaluation of hybrid thermoelectric device systems and environmentally sustainable synthesis methods, to facilitate the practical deployment of MXene-based thermoelectric devices. • A dedicated focus on thermoelectric performance metrics (Seebeck coefficient, electrical/thermal conductivity, power factor, and ZT). • Integration of experimental and computational insights, including band structure engineering and carrier transport mechanisms. • Comparative evaluation of prominent MXene systems such as V₂C, Ti₃C₂, Nb₂C, and Mo₂C, highlighting composition–property relationships. • Extensive use of schematics, comparative tables, and performance maps to enhance accessibility for a broad energy research audience.

Unveiling the impact of bonding asymmetry on the lattice thermal conductivity of MnXS2Cl (X=Sb, Bi) for promising thermoelectric applications

First-principles study of CuMnZ (Z = C, Si, Ge) half-heusler properties for thermoelectric and spintronics applications: exploring tunable functionalities

Lead-free double perovskites have emerged as promising materials for next-generation optoelectronic and energy-conversion technologies because of their chemical tunability, structural stability, and multifunctional physical properties. In this study, the structural, elastic, electronic, optical, and thermoelectric properties of cubic Cs2AlTlX6 (X = I, F) double perovskites were scientifically explored using density functional theory. Structural optimization within the PBE-GGA framework confirms that both compounds are stable in the cubic Fm-3m phase, with Cs2AlTlI6 exhibiting a larger lattice constant and unit-cell volume, whereas Cs2AlTlF6 shows a higher bulk modulus and stronger mechanical rigidity. Elastic-constant analysis satisfies the Born–Huang stability criteria for both systems, indicating mechanical stability; Cs2AlTlI6 displays brittle behavior, while Cs2AlTlF6 exhibits comparatively greater stiffness and marginal ductile character. Electronic properties were analyzed using the TB-mBJ potential reveal indirect band gaps of 2.97 eV for Cs2AlTlI6 and 7.8 eV for Cs2AlTlF6, classifying the iodide compound as a semiconductor and the fluoride analogue as a wide-band-gap insulator. Optical analysis over the 0–40 eV photon-energy range demonstrates pronounced dielectric response, optical conductivity, absorption, refractive-index variation, reflectivity, extinction, and energy-loss features, indicating potential for visible–UV and ultraviolet photonic applications. Thermoelectric transport calculations further show that Cs2AlTlI6 possesses a large positive Seebeck coefficient, an enhanced power factor, and an almost temperature-independent figure of merit close to unity over 100–1000 K, whereas Cs2AlTlF6 exhibits weak thermoelectric efficiency despite its higher electrical conductivity because of its negligible thermopower. Overall, halide substitution strongly governs the multifunctional response of Cs2AlTlX6, with Cs2AlTlI6 emerging as the more favorable candidate for thermoelectric and optoelectronic applications, while Cs2AlTlF6 appears more suitable for ultraviolet optical environments requiring greater mechanical robustness.

The thermoelectric performance of Gallium Nitride (GaN) is inherently limited by its relatively high thermal conductivity and low electrical conductance and thus subsequently decreases its efficiency for power generation from thermal differences. To overcome these limitations, we propose the GaN/WSSe vdW Heterostructure to lower the thermal lattice conductivity and enhance efficiency. Our present work utilizes density functional theory (DFT) to explore structural, electronic, and thermal transport characteristics. The stability of both the monolayer and bilayer structures has been evaluated by analyzing their energetic and thermodynamic stability. The adhesion energy was calculated for the bilayer to verify the most stable stacking model of the GaN/WSSe. The Se-4 and S-3 stacking model has the highest adhesion energies of -508 and -663 meV, respectively, and exhibits staggered (type-II) band alignment, enabling the separation of charge carriers at the interface. Furthermore, the thermoelectric transport characteristic has been analyzed using the nonequilibrium Green's function (NEGF) formalism with the Landauer-Büttiker framework, which describes ballistic quantum transport. The electronic transport channels at the interface suppress the electron scattering, causing a higher Ge of vdWHs and also intermediate thermopower between |S|GaN and |S|WSSe. The Se-4 and S-3 vdWHs enhance the phonon scattering, leading to a decrease in phonon thermal conductance (κph) and consequently resulting in high ZT values of 3.99 and 4.23 having been achieved at higher temperatures. The findings indicate that the GaN/WSSe vdWH holds significant potential for thermoelectric applications.

Herein, the stability, electronic, optical, thermoelectric, and mechanical properties of Cs 2 MBiX 6 (M = Au, Li; X = Cl, Br) are examined using density functional theory (DFT). Thermodynamic and structural stability, as well as the degree of distortion in Cs 2 MBiX 6 , are evaluated using formation and cohesive energies together with tolerance factor analysis. The dynamic stability of these perovskites is confirmed by the positive phonon frequencies obtained from dispersion curves. By applying the Heyd–Scuseria–Ernzerhof 2006 (HSE06) hybrid functional, the optoelectronic properties are analyzed, revealing semiconducting behavior for all studied compounds. An indirect band gap (Eg) of 1.336 eV is obtained for Cs 2 AuBiCl 6 while wider band gaps of 3.913 eV and 4.575 eV are found for Cs 2 LiBiBr 6 and Cs 2 LiBiCl 6 , respectively. The Cs 2 MBiX 6 compounds demonstrate strong light absorption in the ultraviolet (UV) region, indicating their potential for UV-based optoelectronic applications such as photodetectors and UV sensors. To evaluate mechanical stability, the elastic constants are calculated. The Poisson’s ratio (ν) and Cauchy pressure (CP) further indicate ductile behavior for Cs 2 LiBiBr 6 and Cs 2 LiBiCl 6 , whereas Cs 2 AuBiCl 6 shows borderline ductile characteristics. The temperature-dependent electrical conductivity of Cs 2 LiBiCl 6 , Cs 2 AuBiCl 6 , and Cs 2 LiBiBr 6 increases significantly at elevated temperatures, resulting in thermoelectric figure of merit (ZT) values exceeding 0.7 over a wide temperature range. These findings provide useful insight into the potential of Cs 2 MBiX 6 compounds for UV-optoelectronic and thermoelectric applications.

SnTe is widely recognized as a promising alternative to environmentally harmful PbTe for thermoelectric applications at moderate and high temperatures. Nevertheless, due to the ultrahigh hole concentration as well as lattice thermal conductivity, the thermoelectric performance of pure SnTe is greatly constrained. In our work, a novel strategy was put forward to optimize the relatively poor thermoelectric performance of SnTe by simultaneously incorporating In2Se3 and Cd. The Seebeck coefficient was apparently improved through the whole temperature range originating from the introduction of resonant energy levels achieved by In doping, while lattice thermal conductivity was decreased to a relatively low level of ∼0.49 W m–1 K–1 at 873 K, owing to a decrease in sound velocity and strong scattering on phonon caused by nanopores and dislocations after doping. Profiting from the synergistic optimization thermoelectric performance strategies, a peak zT of 1.32 at 873 K was achieved in Sn0.96Cd0.04Te+1%In2Se3, which represents a remarkable 89% increase over pristine SnTe. And an average zT of 0.66 from 303 to 873 K was also obtained. Our work provides a new strategy for multifunctional synergistic modulation of the thermoelectric properties of SnTe-based materials.

The exploration of innovative multifunctional materials for sustainable energy and thermoelectric applications brought about considerable focus on ternary intermetallic compounds because of their tunability as well as durability. In this work, we present a comprehensive first-principles investigation of the structural, electronic, elastic, plasmonic, and thermoelectric transport attributes of the inverse Heusler alloys [Formula: see text] (M[Formula: see text] [Formula: see text] [Formula: see text]Al, In, Zn) using Density Functional Theory (DFT). Structural optimization establishes the energy stability of the inverse Heusler phase, whereas electronic structure analysis indicates a metallic ground state subject to significant p–d orbital hybridization at the Fermi level. The elastic evaluation finds that all three alloys exhibit mechanical stability along with intrinsic ductility, as illustrated by Pugh’s ratios above 1.75. The [Formula: see text] compounds demonstrate significant elastic anisotropy, characterized by a Zener anisotropy factor of 16.44, indicating unique strain-dependent mechanical behaviors. The dielectric functions and electron energy-loss spectra reveal significant bulk plasmon resonances in the Ultraviolet (UV) energy range (10–12[Formula: see text]eV), establishing these materials as potential alternatives for UV plasmonic applications. Additionally, semi-classical Boltzmann transport calculations demonstrate strong electrical conductivity suggestive of metallic properties. Despite the intrinsic Figure of Merit (zT) being small ([Formula: see text]), the presence of pronounced peaks in the transport coefficients suggests that thermoelectric performance can be substantially improved by Fermi level variation. The findings characterize the [Formula: see text] family as versatile multifunctional materials suitable for applications including flexible electronic interconnects, UV-plasmonic applications, and waste heat recovery systems.