Electronic Thermal Conductivity Research Articles

Critical factors influencing electron and phonon thermal conductivity in metallic materials using first-principles calculations.

Understanding the thermal transport of various metals is crucial for many energy-transfer applications. However, due to the complex transport mechanisms varying among different metals, current research on metallic thermal transport has been focusing on case studies of specific types of metallic materials. Ageneral understanding of the transport mechanisms across a broad spectrum of metallic materials is still lacking. In this work, we perform first-principles calculations to determine the thermal conductivity of 40 representative metallic materials, within a range of 8-456 W/mK. Our predicted values of electrical and thermal conductivity are in good agreement with available experimental results. Based on the data of separated electron and phonon thermal conductivity, we employ a statistical approach to examine nine factors derived from previous understandings and identify the critical factors determining these properties. For electrons, although a high electron density of states around the Fermi level implies more conductive electrons, we find it counterintuitively correlates with low electron thermal conductivity. This is attributed to the enlarged electron-phonon scattering channels induced by substantial electrons around the Fermi level. Regarding phonons, we demonstrate that among all the studied factors, Debye temperature plays the most significant role in determining the phonon thermal conductivity, despite the phonon-electron scattering being non negligible in- sometransition metals. Correlation analysis suggeststhat Debye temperature has the highest positive correlation coefficient with phonon thermal conductivity, as it corresponds to a large phonon group velocity. Additionally, Young's modulus is found to be closely correlated with high phonon thermal conductivity and contribution. Our findings of simple factors that closely correlate with the electron and phonon thermal conductivity provide a general understanding of various metallic materials. They may facilitate the discovery of novel materials with extremely high or low thermal conductivity, or be used as descriptors in machine learning to accurately predict the thermal conductivity of metals in the future.&#xD.

A constant self-consistent scattering lifetime in superconducting strontium ruthenate

In this numerical work, we find a self-consistent constant scattering superconducting lifetime for two different values of the disorder parameters, the inverse atomic strength, and the stoichiometric impurity in the triplet paired unconventional super-conductor strontium ruthenate. This finding is relevant for experimentalists given that the expressions for the ultrasound attenuation and the electronic thermal conductivity depend on the superconducting scattering lifetime, and a constant lifetime fits well nonequilibrium experimental data. Henceforth, this work helps experimentalists in their interpretation of the acquired data. Additionally, we encountered tiny imaginary parts of the self-energy that resembles the Miyake-Narikiyo tiny gap out-side the unitary elastic scattering limit, and below the threshold zero gap value of 1.0 meV.

Enhancing Thermoelectric Performance of Mg3Sb2 Through Substitutional Doping: Sustainable Energy Solutions via First-Principles Calculations

Mg3Sb2-based materials, part of the Zintl compound family, are known for their low thermal conductivity but face challenges in thermoelectric applications due to their low energy conversion efficiency. This study addressed these limitations through first-principles calculations using the CASTEP module in Materials Studio 8.0, aiming to enhance the thermoelectric performance of Mg3Sb2 via strategic doping. Density functional theory (DFT) calculations were performed to analyze electronic properties, including band structure and density of states (D.O.S.), providing insights into the influence of various dopants. The semiclassical Boltzmann transport theory, implemented in BoltzTrap (version 1.2.5), was used to evaluate key thermoelectric properties such as the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and electronic figure of merit (eZT). The results indicate that doping significantly improved the thermoelectric properties of Mg3Sb2, facilitating a transition from p-type to n-type behavior. Bi doping reduced the band gap from 0.401 eV to 0.144 eV, increasing carrier concentration and mobility, resulting in an electrical conductivity of 1.66 × 106 S/m and an eZT of 0.757. Ge doping increased the Seebeck coefficient to −392.1 μV/K at 300 K and reduced the band gap to 0.09 eV, achieving an electronic ZT of 0.859 with low thermal conductivity (11 W/mK). Si doping enhanced stability and achieved an electrical conductivity of 1.627 × 106 S/m with an electronic thermal conductivity of 11.3 W/mK, improving thermoelectric performance. These findings established the potential of doped Mg3Sb2 as a highly efficient thermoelectric material, paving the way for future research and applications in sustainable energy solutions.

Investigation of electronic, optical and thermoelectric properties in orthorhombic perovskite SmFeO3

In this work, we have investigated the electronic, optical, and thermoelectric properties of orthorhombic perovskite SmFeO3 using density functional and Boltzmann transport theories, for renewable energy applications. The modeling of the exact electron exchange-correlation has been carried out using both Generalized Gradient Approximation (GGA) and a functional modified with Hubbard interactions. The spin-polarized calculations show that SmFeO3 adopts a G-type antiferromagnetic configuration. The studied compound's electronic band structure and density of states analysis reveal its p-type semiconductor behavior. Furthermore, the optical properties such as real ε1(ω) and imaginary ε2(ω) components of the dielectric function as well as other conventional optical parameters, were investigated. The results show that SmFeO3 is a promising material for optoelectronic applications. The calculated transport properties including the Seebeck coefficient (S), the electrical conductivity (σ/τ), the electronic thermal conductivity (k0/τ) and the electronic figure of merit (ZTe) show significant results. The studied perovskite is also a potential candidate for thermoelectric applications, due to its high Seebeck coefficient, reaching 2388 μV/K, and the large electronic figure of merit which is close to 1 at room temperature. To improve the thermoelectric performance of SmFeO3 material, we have studied the effect of both p-type and n-type doping on its thermoelectric behavior at different temperature values.

Compositionally restricted atomistic line graph neural network for improved thermoelectric transport property predictions

Graph neural networks (GNNs) have evolved many variants for predicting the properties of crystal materials. While most networks within this family focus on improving model structures, the significance of atomistic features has not received adequate attention. In this study, we constructed an atomistic line GNN model using compositionally restricted atomistic representations which are more elaborate set of descriptors compared to previous GNN models, and employing unit graph representations that account for all symmetries. The developed model, named as CraLiGNN, outperforms previous representative GNN models in predicting the Seebeck coefficient, electrical conductivity, and electronic thermal conductivity that are recorded in a widely used thermoelectric properties database, confirming the importance of atomistic representations. The CraLiGNN model allows optional inclusion of additional features. The supplement of bandgap significantly enhances the model performance, for example, more than 35% reduction of mean absolute error in the case of 600 K and 1019 cm−3 concentration. We applied CraLiGNN to predict the unrecorded thermoelectric transport properties of 14 half-Heusler and 52 perovskite compounds, and compared the results with first-principles calculations, showing that the model has extrapolation ability to identify the thermoelectric potential of materials.

Comparative analysis of thermoelectric properties in bulk 2H and monolayer MoS2: a first-principles study at high temperatures

The pursuit of high-efficiency heat-to-electricity conversion is one of the indispensable driving forces toward future renewable energy production. The two-dimensional (2D) transition metal dichalcogenide, such as molybdenum disulfide (MoS2), is at the forefront of research due to its outstanding heat propagation features and potential applications as a thermoelectric material. Using the first-principles density functional theory coupled with the semi-classical Boltzmann transport equation within the constant relaxation time approximation, we present the thermoelectric and energy transport in the bulk 2H and monolayer MoS2 material system. In order to advance the underlying physics, we calculate several crucial transport parameters such as electrical conductivity, electronic thermal conductivity, Seebeck coefficient, and power factor as a function of the reduced chemical potential for different doping types and temperatures, in addition to the electron energy dispersion relation of the material system. Our comprehensive study employs the Shankland interpolation algorithm and the rigid band approximation to attain a high degree of accuracy. This thorough investigation reveals the high Seebeck coefficient of 1534 and 1550 μ V/K at 500 K for the bulk 2H and monolayer MoS2, respectively. Furthermore, the ultrahigh power factor values of 9.21 × 1011 and 3.69 × 1011 Wm −1 K −2 s −1 are shown at 800 K in the bulk 2H and monolayer MoS2, respectively. Based on the power factor results, our in-depth analysis demonstrates that the bulk 2H MoS2, when compared to monolayer MoS2, exhibits great potential as a promising semiconducting thermoelectric material for advanced high-performance energy device applications.

Optical and thermoelectric properties of layer structured Ba2XS4 (X = Zr, Hf) for energy harvesting applications

The main objective of this research is to provide a comprehensive insight into the optical and thermoelectric properties of layer structured Ba2XS4(X = Zr, Hf) for energy harvesting applications using Density Functional Theory (DFT) and semiclassical Boltzmann transport theory. There is a good match between the computed lattice parameters and the available experimental data. Both compounds are thermodynamically and mechanically stable and they are soft, ductile, machinable, and elastically anisotropic. The indirect band gaps are found to be 1.03 eV for Ba2ZrS4 and 1.48 eV for Ba2HfS4. Both compounds possess a mixture of ionic and covalent bonding confirmed by charge density distribution and Mulliken bond population analysis. The maximum absorption is in the ultraviolet regions (∼13.6eV) of light spectra. The total thermal conductivity increases with temperature due to increasing trend of electronic thermal conductivity. The total thermal conductivity at 700 K along c-axis is 4.6 (6.1 W/mK) for Ba2ZrS4 (Ba2HfS4). For p-type Ba2ZrS4 (Ba2HfS4), power factor (PF) is about 7 (5.7) mW/mK2, whereas for n-type it is about 4 (3.9) mW/mK2 at 700 K along c-axis. The power factors of the studied compounds are much higher than those of the reported GeTe and SnSe which would create great interest for further study. The predicted ZT values at 700 K for p-type Ba2ZrS4 and Ba2HfS4 are 0.7 and 0.6, respectively. These values may further be improved through reduction of thermal conductivity and tuning ductility employing known suitable strategies such as alloying and nano-structuring. Finally, Ba2ZrS4 and Ba2HfS4 can be considered new eco-friendly alternatives to previously studied toxic lead-based thermoelectric materials. Their unique advantages of high thermodynamic stability, non-toxic nature and high performance make them strong candidate for sustainable energy solutions.

Electronic, optical, and thermoelectric behaviour of KCuX (X = S, Se, Te) monolayers.

In the past few decades, two-dimensional (2-D) materials gained huge deliberation due to their outstanding electronic and heat transport properties. These materials have effective applications in many areas such as photodetectors, battery electrodes, thermoelectrics, etc. In this work, we have calculated structural, electronic, optical, and thermoelectric properties of KCuX (X = S, Se, Te) monolayers (MLs) with the help of first-principles-based calculations and semi-classical Boltz- mann transport equation (BTE). The phonon dispersion calculations demonstrate the dynamical stability of the KCuX (X = S, Se, Te) MLs. Our results show that the monolayers of KCuX (X = S, Se, Te) are semiconductors with band gaps of 0.193 eV, 0.26 eV, and 1.001 eV respectively, and therefore they are suitable for photovoltaic applications. The optical analysis illustrates that the maximum absorption peaks of the KCuX (X = S, Se, Te) MLs are located in visible and ultraviolet (UV) regions, which may serve as a promising candidate for designing advanced optoelectronic devices. Furthermore, thermoelectric properties of the KCuS and KCuSe MLs, including See- beck coefficient, electrical conductivity, electronic thermal conductivity, power factor, and figure of merit, are calculated at different temperatures 300 K, 600 K, and 800 K. Additionally, we also focus on the analysis of Gru ̈neisen parameter and various scattering rates to further explain their ultra-low thermal conductivity. Our results show that KCuS and KCuSe possess ultra-low lattice thermal conductivity value of 0.15 Wm-1K-1 and 0.06 Wm-1K-1 respectively, which is lower than those of recently reported KAgSe (0.26 Wm-1K-1 at 300 K) and TlCuSe (0.44 Wm-1K-1 at 300 K), indicating towards the large value of ZT. These materials are found to possess desirable thermoelectric and optical properties, making them suitable candidates for efficient thermoelectric and optoelectronic device applications.

Effects of lattice instability on the thermoelectric behavior of kagome metal ScV6Sn6

Kagome metal ScV6Sn6 has been a subject of interest due to the emergence of a first-order structural phase transition with intriguing charge density wave behavior below the transition temperature Tc ∼ 92 K. To explore the thermoelectric properties and provide experimental insights into the nature of the phase transition, we have carried out a combined study by means of the electrical resistivity, Seebeck coefficient, and thermal conductivity measurements on single crystalline ScV6Sn6. Pronounced features near Tc have been characterized by all measured physical quantities. In particular, the Seebeck coefficient exhibits a marked reduction as lowering temperature across Tc, attributed to an imbalance of the contribution from different type of carriers induced by the structural phase transition. From the examination of the electronic and lattice thermal conductivities, we obtained a confirmation that the observed enhancement at Tc is essentially caused by the change of the lattice thermal conductivity, demonstrating the primary importance of lattice distortions for the heat transport of ScV6Sn6. In addition, the lattice thermal conductivity above Tc was found to increase monotonically with temperature. We associated the peculiar phenomenon with lattice fluctuations, highlighting the essence of structural instability in the kagome lattice ScV6Sn6. These results add to the knowledge about the thermal transport properties in kagome materials with a hexagonal HfFe6Ge6-type structure.

Exploring optoelectronic, optical thin films, mechanical and thermal transport properties of bromide double perovskites Rb2Ag(Ga/In)Br6 for photovoltaic and thermoelectric applications

Lead-free double halide perovskites like Rb2Ag(Ga/In)Br6 have demonstrated themselves potential candidates in solar cell research owing to their environmental friendliness, stability, and exceptional performance. This study comprehensively analyzes the structural, mechanical, optoelectronic and optical coating features, as well as thermodynamic and thermoelectric properties of two Rb2AgGaBr6 and Rb2AgInBr6 compounds. Using the Wien2k code with GGA + mBJ exchange-correlation potentials, we confirm their structural stability in cubic phase Fm-3m and identifying them as direct band gap semiconductors (Γ → Γ) of 0.38 eV and 1.0644 eV, respectively. Then, optical analysis reveals broad absorption bands across visible and ultraviolet wavelengths, making them suitable for photovoltaic absorbers. Finally, the thermoelectric investigations under varying temperatures show favourable properties, such as a high Seebeck coefficient with poor electronic thermal conductivity. This also yields exceptional value (0.96 and 0.994 for Rb2AgGaBr6, Rb2AgInBr6, respectively) of figure of merit (ZT) at room temperature and chemical potential μ-μ0 = - 0.09eV near the Fermi energy level, enhancing their potential for thermoelectric applications. These findings underscore the versatility and promising future of Rb2Ag(Ga/In)Br6 as important semiconductors processing for optoelectronic, thermoelectric, and mechanical devices.

Thermoelectric Characteristics of Permingeatite Compounds Double-Doped with Sn and S.

Sn/S double-doped permingeatites, Cu3Sb1-xSnxSe4-ySy (0.02 ≤ x ≤ 0.08 and 0.25 ≤ y ≤ 0.50) were synthesized, and crystallographic parameters and thermoelectric characteristics were examined as a function of doping level. The lattice parameters of permingeatite were significantly modified by the dual doping of Sn and S, with S doping exerting a greater influence on lattice constants and variations in tetragonality compared to Sn doping. With an increase in the level of Sn doping and a decrease in S doping, the carrier concentration increased, leading to enhanced electrical conductivity, indicative of a degenerate semiconducting state. Conversely, an increase in S doping and a decrease in Sn doping led to a rise in the Seebeck coefficient, demonstrating p-type conductivity characteristics with positive temperature dependence. Additionally, the double doping of Sn and S substantially improved the power factor, with Cu3Sb0.98Sn0.02Se3.75S0.25 exhibiting 1.12 mWm-1K-2 at 623 K, approximately 2.3 times higher than that of undoped permingeatite. The lattice thermal conductivity decreased with increasing temperature, while the electronic thermal conductivity exhibited minimal temperature dependence. Ultimately, the dimensionless figure of merit (ZT) was improved through the double doping of Sn and S, with Cu3Sb0.98Sn0.02Se3.50S0.50 recording a ZT of 0.68 at 623 K, approximately 1.7 times higher than that of pure permingeatite.

Calculation on power factor and figure of merit in a single-layer NiBr2

Abstract Implementation of the classical Boltzmann transport theory has been performed to calculate the power factor, as well as the figure of merit in a single-layer NiBr2 after performing density functional theory. Those two properties were formulated from the Seebeck coefficient, electron thermal conductivity, and electrical conductivity. An in-plane ferromagnetic formation of magnetic moments in the Ni atoms was applied in the primitive cell. We found a small power factor, but a high figure of merit at the Fermi level near critical temperature. Since the efficiency of thermoelectric materials is represented by the figure of merit, a single-layer NiBr2 is a strong candidate for thermoelectric materials which can be applied in future devices.

Theoretical Studies of the Electronic and Thermoelectric Properties of PrIn3 and NdIn3 in Cubic Phase

The electronic and thermoelectric properties of AB3 (A =Pr, Nd and B=In) materials (crystallizing in the cubic structure) having space group Pm-3m (221) are studied using B3PW91 hybrid functional through the Full-Potential Linear Augmented Plane Wave (FP-LAPW) approach within the framework of Density Functional Theory (DFT). The calculated lattice parameters for PrIn3 and NdIn3 are 4.5668 Å and 4.5539 Å respectively. Electron-electron correlation effect is due to the 4f orbitals present in these materials and therefore, with the use of B3PW91 hybrid functional, band structure and density of states are calculated. When analyzing electron charge density, these materials showed a stronger ionic character. Band structure and density of state analysis confirms the metallic nature of the materials. Using the semi-empirical Boltzmann approach implemented in the BoltzTraP code, the thermoelectric parameters, such as Seebeck coefficient, figure of merit, electrical conductivity per relaxation time, and electronic thermal conductivity per relaxation time as a function of chemical potential, were computed at 500 K temperature gradient. PrIn3 showed highest Seebeck coefficient value, 50.68 μV/K among these compounds. The peak value of electrical conductivity per relaxation time and electronic thermal conductivity per relaxation time among these compounds is calculated for NdIn3 is 2.43 x 1020 1/Ωms and 22.50×1014 W/mKs.

Improving thermoelectric performance of α−T3 structure via integration of the Kane-Mele-Hubbard model

Our research examines the electronic thermal conductivity, electrical conductivity, Seebeck coefficient, and figure of merit of the α-T3 structure utilizing the Green's function approach within the Hamiltonian framework of the Kane-Mele (KM) and Hubbard models. We evaluate how variations in chemical potential, on-site Coulomb repulsion (OSCR) strength, and spin-orbit coupling (SOC) parameters influence these properties. Our findings uncover interesting trends: the presence of a flat band at the energy level of zero within this structure and the gap between the flat band and other bands is observed. The observable rise in SOC results in a clear division within the energy band, demonstrating the notable impact SOC exerts on the electronic structure of the system.Moreover, this strategy displays that this material's thermoelectric properties increase due to temperature, SOC, and OSCR. Also, it was observed that augmenting the α parameter can enhance both thermoelectric and thermopower.

DFT study of the brownmillerite-type strontium-based oxygen-deficient perovskites SrTMO2.5 (TM = Mn, Fe, Co and Cu)

DFT studies are performed to investigate the crystal structure and geometry, electronic and magnetic properties of brownmillerite-type strontium-based oxygen-deficient perovskites [Formula: see text] (TM = Mn, Fe, Co and Cu) in orthorhombic phase. The comparison of the calculated lattice parameters shows consistency with the experiments, and all these perovskites are thermodynamically stable as revealed by cohesive energy. The spin-dependent calculations of the electronic band profiles demonstrate the metallic behavior of all these deficient perovskites. The increase in electrical resistivity and electronic thermal conductivities with temperature also confirms the metallic behavior of these compounds. The optimized ground state energies in different magnetic phases and post-DFT treatment confirm that [Formula: see text] and [Formula: see text] are stable in C-type AFM, [Formula: see text] is in G-type AFM and [Formula: see text] in A-type AFM phase, respectively. The high specific heat of these deficient perovskites makes them good candidates for high-temperature technology. Based on the above physical properties, it is expected that these deficient perovskites are potential candidates for spintronics and magnetic storage devices.

Enhanced thermoelectric properties of Ag2Se by manipulation in carrier concentration via acetylene carbon black nanocomposites

Pristine Ag2Se has inherent limitations in its Seebeck coefficient and electronic thermal conductivity, necessitating improvements through carrier concentration manipulation. While its porous structure has been utilized to reduce carrier concentrations, achieving optimal values remains challenging. This study explores enhancing Ag2Se with acetylene carbon black (ACB) nanocomposites to further reduce carrier concentrations and improve thermoelectric (TE) properties. ACB, a cost-effective alternative to other carbon materials, has demonstrated potential in enhancing TE performance in various composites. Ag2Se and ACB composites were synthesized by dispersing different ACB weights in a solution, followed by sintering. Characterization using x-ray diffraction (XRD), Transmission and scanning electron microscopy (TEM and SEM), and other techniques confirmed the phase, structure, and morphology of the composites. The addition of ACB resulted in decreased electrical conductivity and increased Seebeck coefficient in Ag2Se, particularly at ACB concentrations up to 5.0 wt%, balancing the power factor (PF). The total thermal conductivity decreased due to mainly reduced electronic thermal conductivity. The 5.0 wt% ACB sample achieved a zT of approximately 0.8 at 383 K, comparable to the performance of composites using more expensive low-dimensional carbon materials.

Analytical study of the thermoelectric properties in silicene

Theoretically, we investigate the thermoelectric (TE) properties namely, electrical conductivity (σ), diffusion thermopower (S d), power factor (PF), electronic thermal conductivity (κ e) and thermoelectric figure of merit (ZT) for silicene on Al2O3 substrate. TE coefficients are obtained by solving the Boltzmann transport equation taking account of the electron scattering by all the relevant scattering mechanisms in silicene, namely charged impurity (CI), short-range disorder (SD), intra- and inter-valley acoustic (APs) and optical (OPs) phonons, and surface optical phonons (SOPs). The TE properties are numerically studied as a function of temperature T (2–400K) and electron concentration n s(0.1–10 × 1012 cm−2). The calculated σ and S dare found to be governed by CIs at low temperatures (T< ∼ 10 K), similar to that in graphene. At higher T, they are found to be mainly dominated by the intra- and inter-valley APs. The resultant σ (S d) is found to decrease (increase) with increasing T, whereas PF remains nearly constant for T> ∼ 100 K. On the other hand, n s dependence shows that σ (S d) increases (decreases) with increasing n s; with PF relatively constant at lower n s and then decreases with increasing n s. At room temperature, the calculated σ (S d) in silicene is closer to that in graphene and about an order of magnitude greater (less) than that in monolayer (ML) MoS2. The κ e is found to be weakly depending on T and Wiedemann–Franz law is shown to be violated. We have predicted a maximum PF ∼3.5 mW m−1 K−2, at 300 K for n s = 0.1 × 1012 cm−2 from which the estimated ZT = 0.11, taking a theoretically predicted lattice thermal conductivity κ l = 9.4 Wm−1 K−1, is a maximum. This ZT is much greater than that of graphene and ML MoS2. The ZT is found to decrease with the increasing n s. The ZT values for other values of n s in silicene, at 300 K, also show much superiority over graphene, thus making silicene a preferred thermoelectric material because of its relatively large σ and very small κ l.

Synergistic strategy via modulated energy filtering and hierarchical defects evolution for high performance GeTe thermoelectrics

GeTe thermoelectric materials are very promising for sustainable waste-heat harvesting, while optimizations have been focusing on lowering lattice thermal conductivity or decreasing carrier concentration. As a long-pursued strategy to improve electronic transport properties, the full realization of effective energy filtering has been hindered by the mismatch between the energy barriers introduced and the intrinsic Fermi level of the matrix material. In this work, a synergistic strategy combining modulated energy filtering effect and hierarchical defect evolution engineering leads to ultrahigh performance GeTe-based thermoelectric materials. Very effective energy filtering is achieved by incorporating carbon fibers, which increases the overall energy of charge carriers. This greatly enhances Seebeck coefficient to over 230 μVK-1 with minor reduction in electrical conductivity which simultaneously decreases electronic thermal conductivity. Furthermore, the inclusion of carbon fibers modulates the microstructure of GeTe and facilitates the evolution of point defects to higher dimensional defects for broadband phonon scattering, greatly suppressing the lattice thermal conductivity to 0.3 Wm-1K-1. This strategy yields a prominent thermoelectric figure of merit ZTmax ∼ 2.3 and an exceptional quality factor Bmax ∼ 2.24 for Ge0.97Bi0.07Te with 0.9 wt% carbon fibers. This study demonstrates a promising strategy to modulate the convoluted thermoelectric properties for ultrahigh performance thermoelectric materials.

Study of the physical properties of the half-heusler XBrH with (X= sr, Ca and mg) compounds

Half-Heusler alloys are among the most promising thermoelectric materials for medium- and high-temperature waste heat recovery applications. This study investigates the physical properties of Half-Heusler compounds XBrH, with X = Sr, Ca, and Mg. We explored the structural, electronic, optical, and thermoelectric properties of these compounds using density functional theory (DFT) as implemented in the Wien2k package. The Generalized Gradient Approximation (GGA) as proposed by Perdew-Burke-Ernzerhof (PBE) and the modified Becke-Johnson (mBJ) functional were employed to calculate the exchange-correlation interactions. After doing structural optimization for a range of parameters, we discovered that the SrBrH compound is more stable than the CaBrH and MgBrH compounds. Our results show that the density of state calculations indicate semiconductor behavior for the XBrH with (X = Sr, Ca, and Mg) compounds. We also evaluated the real and imaginary parts of the dielectric tensor, the refractive index, the absorption coefficient, the electron energy loss, and the real and imaginary components of the optical conductivity, among other optical parameters. Additionally, we investigated the figure of merit (ZT), electronic and lattice thermal conductivity, Seebeck coefficient, and electrical conductivity. The MgBrH, CaBrH and SrBrH compounds showed p-type behavior, with positive values for the Seebeck coefficient and the greatest value of ≈180 μV/K, according to the thermoelectric data. At 1000 K, the ZT reach their highest values for CaBrH, SrBrH, and MgBrH, respectively, at 2.9, 2.8, and 0.9. The physical properties of the XBrH with (X = Sr, Ca, and Mg) compounds have been studied in detail.

Thermoelectric Performance of Non-Stoichiometric Permingeatite Cu3+mSbSe4.

Non-stoichiometric permingeatites Cu3+mSbSe4 (-0.04 ≤ m ≤ -0.02) were synthesized, and their thermoelectric properties were examined depending on the Cu deficiency. Phase analysis by X-ray diffraction revealed no detection of secondary phases. Due to Cu deficiency, the lattice parameters of tetragonal permingeatite decreased compared to the stoichiometric permingeatite, resulting in a = 0.5654-0.5654 nm and c = 1.1253-1.1254 nm, with a decrease in the c/a ratio in the range of 1.9901-1.9903. Electrical conductivity exhibited typical semiconductor behavior of increasing conductivity with temperature, and above 423 K, the electrical conductivity of all samples exceeded that of stoichiometric permingeatite; Cu2.96SbSe4 exhibited a maximum of 9.8 × 103 Sm-1 at 623 K. The Seebeck coefficient decreased due to Cu deficiency, showing p-type semiconductor behavior similar to stoichiometric permingeatite, with majority carriers being holes. Thermal conductivity showed negative temperature dependence, and both electronic and lattice thermal conductivities increased due to Cu deficiency. Despite the decrease in the Seebeck coefficient due to Cu deficiency, the electrical conductivity increased, resulting in an increase in the power factor (especially a great increase at high temperatures), with Cu2.97SbSe4 exhibiting the highest value of 0.72 mWm-1K-2 at 573 K. As the carrier concentration increased due to Cu deficiency, the thermal conductivity increased, but the increase in power factor was significant, with Cu2.98SbSe4 recording a maximum dimensionless figure-of-merit of 0.50 at 523 K. This value was approximately 28% higher than that (0.39) of stoichiometric Cu3SbSe4.