Thermoelectric Applications Research Articles

Significantly Enhanced Thermoelectric Performance of p-Type Mg3Sb2 via Zn Substitution on Mg(2) Site: Optimization of Hole Concentration Through Ag Doping.

n-Type Mg3Sb2-based thermoelectric materials have recently garnered significant interest due to their superior thermoelectric efficiency. Yet, the advancement of p-type Mg3Sb2 for thermoelectric applications is impeded by its lower dimensionless figure of merit (zT). In this study, we demonstrate the improved thermoelectric performance of p-type Mg3Sb2 through the strategic optimization of Zn content and Ag doping on the Mg/Zn(2) site. Initially, samples of Mg3-xZnxSb2 (x = 0, 0.5, 1.0, and 1.5) were synthesized via elemental reactions within a Pyrex tube, followed by densification through hot pressing. X-ray diffraction analysis confirmed that the Mg3-xZnxSb2 phases retain the same Pm1 space group as the pristine Mg3Sb2 phase. The strategic substitution of Zn improved the power factor via band convergence and reduced lattice thermal conductivity by introducing point defect phonon scattering. This led to a peak zT of 0.5 at 725 K, with an average zT of 0.25 across the 325-725 K range. Enhancement in carrier concentration was achieved by doping Ag onto the Zn site, culminating in a peak zT of 0.95 at 725 K and an average zT of 0.46 between 325 and 725 K for the Mg2Zn0.97Ag0.03Sb2 sample. This performance surpasses that of most p-type Mg3Sb2-based materials, markedly advancing the potential for Mg3Sb2-based materials in midtemperature heat recovery thermoelectric generators.

Effect of AFM ordering on thermoelectric responses of Mg3X2 (X: C, Si, Ge) monolayers : a DFT insight

Two-dimensional materials have gained a lot of attention in the last few decades due to their potential applications in thermoelectric and nano-electronic devices. This study systematically presents the mechanical, electronic and thermoelectric characteristics of two-dimensional honeycomb-kagomeMg3X2(X:C,Si,Ge) structures in the framework of density functional theory computations and by solving semiclassical Boltzmann transport equation. The geometrical stability of these structures is validated by phonon spectrum and molecular dynamics simulations. Following the elastic constants, we have inferred that all the systems are mechanically stable and brittle in nature. Lower values of Debye temperature of all structures suggest thatMg3X2monolayers should have lower values of lattice thermal conductivity compared to graphene. Electronic structure calculations indicate that these materials are semimetallic in their nonmagnetic phase. All the structures display remarkably low lattice thermal conductivity (0.9-1.5 W (mK)-1) due to a large scattering factor and higher anharmonicity. The presence of sharp density of states peaks close to the Fermi level, arising from nearly flat and dispersionless band in the antiferromagnetic (AFM) arrangement, is poised to enhance the Seebeck coefficient, thereby potentially boosting the thermoelectric performance. The estimated values of thermoelectric figure of merit (ZT) are around 0.78 and 0.67 forMg3Si2andMg3Ge2structure respectively in AFM phase atT= 700 K. These outcomes of our findings suggest thatMg3X2monolayers exhibit substantial promise for thermoelectric device application.

Evaluation of Processing Parameters in the Solvothermal Synthesis of Cu-Rich Tetrahedrites for Potential Application as Thermoelectric Materials

The major issue associated with thermoelectric performance is the low efficiency of power conversion. The main challenge is achieving a combination of high Seebeck coefficient, high electrical conductivity, and low thermal conductivity for a significantly improved figure of merit (ZT). Developing strategies include the production of tetrahedrites with an intrinsically low thermal conductivity through the solvothermal method, using a low reaction time and processing temperature. Here, we report on the preparation of Cu-rich tetrahedrites through the solvothermal technique at low temperature, providing a promising strategy for the preparation of materials with potential applications in thermoelectricity. The influence of synthesis reaction time and temperature on the morphological, structural, and thermoelectrical properties of the samples was investigated through different characterization techniques. Tetrahedrite synthesized at 180 °C for 19 h yielded a favorable ZT value of >0.43 and a thermal conductivity of 0.2 Wm−1 K−1 (423 K), related to the Sb3+/Sb5+ and Cu+/Cu2+ ratio, as was observed by XPS. The cubic tetrahedrite phase attributed to the (222) plane was confirmed by XRD and TEM and the intense Raman mode observed at 351 cm−1. SEM images revealed that nanotetrahedral Cu-rich tetrahedrites efficiently assemble into spherical structures, resulting in an improvement in the Seebeck coefficient (437 µVK−1) and electrical conductivity.

Understanding the Ultralow Thermal Conductivity and Strong Anharmonicity of a Lanthanum-Based Germanium Halide Monolayer for Possible Thermoelectric Applications

Understanding the Ultralow Thermal Conductivity and Strong Anharmonicity of a Lanthanum-Based Germanium Halide Monolayer for Possible Thermoelectric Applications

KCaAs and KCaP: promising half-Heusler compounds for UV protection and thermoelectric applications

This study investigates the structural, electrical, optical, and thermoelectric properties of the half-Heusler compounds KCaAs and KCaP using the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method within the framework of density functional theory. Our analysis reveals that both compounds exhibit favourable characteristics for high-performance applications. Specifically, KCaAs and KCaP show high static refractive indices and significant reflectivity in the ultraviolet (UV) range, making them ideal for UV protection and optical devices. Thermoelectric analysis indicates that both materials are p-type semiconductors with high Seebeck coefficients at low temperatures, high electrical conductivity, and relatively low thermal conductivity. The temperature-dependent figure of merit ( ZT ) reveals robust thermoelectric performance across a wide temperature range, with maximum ZT values of approximately 0.77 for both compounds. These results suggest that KCaAs and KCaP are promising candidates for thermoelectric applications, offering significant potential for energy conversion and sustainable energy solutions.

Evaluating Sulfur as a P‐Type Dopant in Cu3N Using Ab Initio Methods

Copper nitride (Cu3N) is an environmentally friendly semiconducting material with bipolar doping capability and is of interest to various applications. As deposited Cu3N films have inherent n‐type conductivity, further controllable n‐type doping is possible by introducing metal impurities. First‐principles methods based on density functional theory and beyond have been employed to study the p‐type doping behavior of sulfur atoms in Cu3N. The structural, electronic, optical, and thermal properties of pure Cu3N and sulfur‐doped Cu3N are computed for single and 3 × 3 × 3 supercells. Sulfur doping causes a shift from intrinsic n‐type to p‐type behavior. This study confirms that sulfur atoms in sulfur‐doped copper nitride preferentially occupy interstitial positions over nitrogen substitution, face‐centered, or copper substitution sites. Due to this change and an increased lattice constant, Cu3N becomes a softer material with a larger bandgap in the single‐cell alloy. Doped Cu3N supercell results show significant changes in optical properties appropriate for solar and other photoelectric applications. Cu3N:S exhibits remarkable enhancements in power factor and thermal and electrical conductivity, indicating potentially better performance in thermoelectric applications. The dielectric constant and absorption coefficient also significantly change with the incorporation of sulfur into Cu3N.

La2O2MQ2 phases: Stability and synthetic challenges

Oxychalcogenides containing transition metal or p block cations have potential for thermoelectric, photocatalytic and magnetic applications but the synthetic pathways to these quaternary phases are not fully understood. This presents a challenge to the design and preparation of new functional materials. Our combined experimental and computational study of La2O2MQ2 (M = +2 cation; Q = sulfide, selenide anion) systems explores the thermodynamic constraints on synthesis and highlights the subtle balance in stabilities of phases formed via competing reaction pathways.

Copper-catalyzed plastic waste synthesized graphene nanosheets/polypyrrole nanocomposites for efficient thermoelectric applications

Presently, various catalysts have been reported for the synthesis of carbon nanomaterials from a variety of plastic waste, which needs to be removed at the end of the synthesis process by using chemical techniques and hence make the process more typical from the aspect of cost-benefit and circular economic aspects. Herewith, we report copper turnings as the cost-effective and greener catalytic templates for synthesizing highly conducting graphene nanosheets (GNs). The synthesis of the GNs from plastic waste was done as we previously reported in the steps of the pyrolytic process, where the copper turnings are used as catalytic templates in the present study. Because of the excellent catalytic efficiency towards breaking old carbon-carbon bonds and forming new carbon-carbon bonds, the copper turnings act as an excellent degradation catalyst and promote the growth of graphitic skeletons and, consequently, graphene nanosheets. The synthesized GNs showed a high conductivity of ∼ 1730 S/m. GNs thus synthesized is implemented for synthesizing GNs/polypyrrole nanocomposites, which is later investigated for the TE applications. The values of the Seebeck coefficient showed that the composite of GNs/polypyrrole performs as a p-type semiconductor. The TE figure of merit (ZT) for GNs/polypyrrole demonstrated good thermoelectric characteristics and showed a value of 3.75 × 10−6 at the temperature. Thus, the present method of synthesis of GNs showed a more convenient, industrial friendly technique for the production of plastic waste derived graphene nanosheets and its application for thermal energy conversion applications.

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.

Structural, electronic, optical and thermoelectric properties of FrSnI3-xFx (X=0, 1, 2, 3) perovskites using the TB-mBJ approach

In this study, we investigate the structural, optical, electronic, and thermoelectric properties of FrSnI3-xFₓ (x = 0, 1, 2, 3) perovskites using density functional theory with the modified Becke-Johnson method (TB-mBJ) for exchange correlation functions. This research is the first theoretical investigation of these promising materials. Our results show that each variant of the perovskite exhibits p-type semiconductor behavior, and that the energy gap of FrSnI₃ can be tuned by substituting an iodine atom with fluorine. This substitution causes a significant variation in the energy gap, ranging from 1.169 eV to 2.951 eV. In particular, the FrSnI₂F compound stands out with a direct gap of 1.539 eV, making it an ideal candidate for solar cell applications. Optical properties, including real and imaginary dielectric function components, absorption and refractive indices, highlight the performance of these materials. Their high absorption capabilities suggest that these perovskites can be tailored and integrated into optical and optoelectronic devices in a variety of spectral ranges.Furthermore, thermoelectric property calculations using BoltzTrap software show that FrSnI3-xFₓ (x = 0, 1, 2, 3) has a promising Seebeck coefficient and an impressive figure of merit approaching unity at high temperatures. These results underscore the immense potential of these materials in thermoelectric applications, opening the door to new possibilities in energy conversion technology.

Thermally Driven Spin Transport of Epitaxial FeRh Films with a Non-magnetic Pt Layer via the Longitudinal Spin Seebeck Effect.

FeRh has been demonstrated to be an important material for the observation of magnetic phase transitions, such as the first-order transition from an antiferromagnetic (AFM) to a ferromagnetic (FM) state, in response to changes in the temperature. This is because of the magnetic moment induced in Rh atoms above the magnetic phase transition temperature. In the present study, we focus on the longitudinal spin Seebeck effect (LSSE), which involves the generation of spin voltage as a result of a temperature gradient in FM materials or FM insulators, and experimentally assess the effect of the crystalline quality of FeRh films and the properties of the substrate on the LSSE thermopower during the FM-AFM phase transition. The measured LSSE thermopower of an epitaxial (110)-oriented FeRh film grown on an Al2O3 substrate is approximately 60 times higher than that of a polycrystalline FeRh film on a SiO2/Si substrate. This can be explained by the high magnetic sensitivity and superior FM properties of (110)-oriented epitaxial FeRh films. Furthermore, by comparing the transverse thermoelectric voltage for in-plane magnetized (IM) and perpendicularly magnetized (PM) configurations, we quantitively evaluate the contribution of the exclusive anomalous Nernst effect (ANE) to the LSSE signals in the FeRh/Al2O3 structure, finding it to be approximately 15-30% over a temperature range of 75-300 K. LSSE measurements in Pt/FeRh films are thus demonstrated to provide a versatile pathway for the development of thermoelectric power generation applications and other practical spintronics and neuromorphic computing devices.

Ultrahigh‐Pressure Structural Modification in BiCuSeO Ceramics: Dense Dislocations and Exceptional Thermoelectric Performance

AbstractDislocations as line defects in crystalline solids play a crucial role in controlling the mechanical and functional properties of materials. Yet, for functional ceramic oxides, it is very difficult to introduce dense dislocations because of the strong chemical bonds. In this work, the introduction of high‐density dislocations is demonstrated by ultrahigh‐pressure sintering into a typical ceramic oxide, BiCuSeO, for thermoelectric applications. The ultrahigh‐pressure induces shear stresses that surpass the critical strength for dislocation nucleation, followed by dislocation glide and profuse multiplication, leading to a high dislocation density of ≈9.1 × 1016 m−2 in Bi0.96Pb0.04CuSeO ceramic. These dislocations greatly suppress the phonon transport to reduce the lattice thermal conductivity, reaching 0.13 Wm−1 K−1 at 767 K and resulting in a record‐high zT of 1.69 in this oxide thermoelectric ceramic. This study demonstrates the feasibility of generating dense dislocations in ceramic oxides via ultrahigh‐pressure sintering for tuning functional properties.

Low lattice thermal conductivity induced by rattling-like vibration in Zintl phase Na2CaCdSb2 compound with high ZT from two-channel model

Zintl phase compounds, characterized by the traits of a phonon-glass and electron-crystal, stand out as promising candidates for thermoelectric applications. This study delves into the thermoelectric properties of Zintl phase Na2CaCdSb2 compound through a synergy of first-principles calculations, machine learning interatomic potential approach based on the two-channel model, and high-throughput screening calculations. With an indirect bandgap of 1.02 eV, Na2CaCdSb2 compoundpossesses an high carrier mobility. The high valence band degeneracy and anisotropic band (light-heavy band) lead to a high power factor for the p-type Na2CaCdSb2 compound. The strong fourth-order anharmonicity of the rattling-like Na atom manifests the low lattice thermal conductivity on the basis of two-channel model. The loosely bonding Na atom displays random rotations and dynamically disordered orientations, leading to the weakly disordered nature of Na2CaCdSb2 compound. The unique crystal structure of Na2CaCdSb2 compound coupled with the abundance of diffusion-like phonons play a pivotal role in the phonon transport. Considering the low lattice thermal conductivity and high power factor with the framework of two-channel model, the n-type and p-type Na2CaCdSb2 compounds exhibit optimal figure-of-merits (ZT) of 1.0 and 2.0 at 600 K, showcasing excellent thermoelectric performance. Meanwhile, an optimal ZT of 2.3 is achieved for p-type Na2CaCdSb2 compound at the same temperature along the x-direction. Our present study not only provides fundamental insights into the thermal and electronic transport properties of Na2CaCdSb2 compound under the two-channel model in combination with the four-phonon scattering and multiple carrier scattering rates, but also rationalizes the high-order phonon interactions and thermal transport properties under two-channel model.

Analysis of Thermoelectric Properties of Hot-deformed Bismuth Telluride Sintered Materials

Bismuth telluride (Bi2Te3)-based alloys are widely used for thermoelectric cooling and power generation at low temperatures, and they are the only commercially available materials for thermoelectric applications below 500 K. The rhombohedral unit cell with a large c/a lattice constant ratio consisting of - Te-Bi-Te-Bi-Te- stacked layers inevitably brings about a large anisotropy in transport properties, which is why texturing is very important in polycrystalline Bi2Te3</sub alloys for maximum performance. In this report, p and n-type polycrystalline Bi2Te3</sub alloys were synthesized and hot-deformed to investigate the effects of texturing on thermoelectric properties. Hot deformation (HD) induces the strong alignment of (001) orientations along the compression direction, and a remarkable increase in the orientation factor F of (001) orientations is observed after HD in both p and n-type materials. All of the hot-deformed polycrystalline samples showed increased electrical conductivity (σ), power factor (PF), and thermal conductivity (k) in the in-plane (IP) direction, and vice versa in the out-of-plane (OOP) direction, which makes the IP direction of the hot-deformed bodies more favorable for module fabrication in terms of power factor, for both p and n-type Bi2Te3</sub-based alloys. However, due to the different degree of anisotropy of k and σ, the figures of merit (zT) were maximized in the OOP direction in the p-type materials after HD, whereas the zTs of the n-type materials were higher in the IP direction. This occurs because the anisotropy factor of electron conduction is higher than that of hole conduction, which more than offsets the advantage of the smaller k in the c-direction of n-type Bi2Te3</sub. The maximum zT of 1.33 (OOP) and 0.90 (IP) were obtained after HD from the p and n-type Bi2Te3 alloys, respectively, which were 9.3% and 18.4% higher than those of as-sintered materials.

Magnetron sputtered Zn-Ta2O5 thin films for electronic, thermoelectric, and optical applications

In the current study, the optical and electronic properties of Zn-Ta2O5 have been investigated as a potential optoelectronic material. Theoretically, the density functional theory was employed to pure and Zn doped Ta2O5 compositions using the Wien2k code. For experimental investigations uniform thin films were fabricated by magnetron co-sputtering technique on the silicon substrate. The optical, thermoelectric, electronic, and morphological properties were studied by relating the outcomes of simulations and experimental results providing the correlation among the findings. Graphs of the total density of states and partial density of states revealed the hybridization between the dopant and host orbitals. The p-d hybridization of O and Ta atoms was shown by the density of states. Structural studies reveal the growth of primary phase identified as orthorhombic Ta2O5. The grain growth of the Zn-Ta2O5 thin films gradually increase as the Zn content was increased and led to more compact film formation. Zn incorporation improves the thermal transport properties by increasing the Seebeck coefficient and reducing thermal conductivity. Band gap values were reduced by increasing the Zn concentration and recorded value was observed as 3.07 eV for Ta2O5 and 1.77 eV for maximum zinc concentration. Optical characteristics are measured in relation to photon energy which shows enhancement by the Zn doping. The outcomes of the current study manifest that these materials provide great potential for thermoelectric and optoelectronic applications.

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.

Chemical Pressure-Driven Band Convergence and Discordant Atoms Intensify Phonon Scattering Leading to High Thermoelectric Performance in SnTe.

SnTe is an intriguing alternative to PbTe for midtemperature thermoelectric applications. Despite steady progress, its performance is lagging, in part because of the large energy difference(ΔEL-Σ) between the light (L-band) and heavy (Σ-band) valence bands and higher lattice thermal conductivity (κL). Previous studies have shown that applying pressure can enhance the Seebeck coefficient (S) and power factor (PF) of SnTe. Inspired by this study, we showcase how the high-pressure effect can be emulated under ambient pressure by substituting Sn with atoms possessing smaller atomic radii. Specifically, Sb- and Ge-doping combined with CdTe- or CdS-alloying induce lattice shrinkage, also referred to as "chemical pressure", raising the energy of the Σ-band. Additionally, these substituted atoms lower the contribution of Sn 5s-Te 5p antibonding states to the L-band, thereby reducing its energy and dispersion. These combined effects decrease ΔEL-Σ from 0.36 to 0.09 eV, leading to the enhanced S and average PFavg. Notably, the PFavg, ranging from 323 to 873 K, increases from 8.1 μW cm-1 K-2 for pristine SnTe to 21.6 μW cm-1 K-2 for Sn0.79Ge0.15Sb0.06Te-5% CdTe. Furthermore, the intensified phonon scattering resulting from discordant nature of Ge and Cd atoms, creating point defects soften phonon modes, and the presence of Ge-rich nanoprecipitates lead to a substantial 62% reduction in κL at 873 K. This strong valence band convergence and enhanced phonon scattering collectively contribute to a high peak ZT of 1.5 (873 K) and high average ZTavg = 0.81 over the temperature range of 323-873 K.

Achieving ZT > 1 in Cu and Ga Co-doped Ag6Ge10P12 with Superior Mechanical Performance and Its Fundamental Physical Properties toward Practical Thermoelectric Device Applications.

Recently, phosphorus-based compounds have emerged as potential candidates for thermoelectric materials. One of the key challenges facing this field is to achieve ZT > 1, which is the benchmark for thermoelectric device applications. In this study, it is demonstrated that the thermoelectric performance of environmentally friendly Ag6Ge10P12 is enhanced by co-doping Cu and Ga. The mechanical properties, coefficient of linear thermal expansion, work function, and compatibility factor are comprehensively clarified to provide guidelines for reliable device applications. The peak and average dimensionless figures of merit of Ag5.85Cu0.15Ge9.875Ga0.125P12 reach 1.04 at 723 K and 0.63 at 300-723 K, respectively, which are the highest values for phosphorus-based thermoelectric materials. The Young's modulus, Vickers microhardness, fracture toughness, and compressive strength of Ag5.85Cu0.15Ge9.875Ga0.125P12 are 132 GPa, 589, 1.23 MPa m1/2, and 219 MPa, respectively, which are superior to those of typical state-of-the-art thermoelectric materials. The remarkable thermoelectric and mechanical performance of Ag5.85Cu0.15Ge9.875Ga0.125P12 mean that it is a promising candidate for medium-temperature thermoelectric conversion. Ti, V, Rh, and Pt are suitable for electrodes without exfoliation under thermal expansion and with ohmic contacts to Ag5.85Cu0.15Ge9.875Ga0.125P12 in terms of the coefficient of linear thermal expansion and work function. Considering that the compatibility factor of Ag5.85Cu0.15Ge9.875Ga0.125P12 is approximately 2.8, half-Heusler, skutterudite, and magnesium silicide-stannide compounds are suitable n-type thermoelectric counterpart materials in thermoelectric devices. These insights will lead to the development of phosphorus-based thermoelectric materials toward practical thermoelectric device applications.

Experimental analysis of free-standing and substrate-constrained Ga-doped ZnO nanostructured thermoelectric films

Developing thermoelectric films without substrates—free-standing films—eliminates substrate-induced effects on performance and meets the flexibility requirements of emerging wearable thermoelectric applications. This study investigates Gallium-doped Zinc Oxide (GZO), composed of abundant and non-toxic elements, to fabricate a substrate-free GZO film via 3D printing and compares its structural, chemical, and thermoelectric properties with those of a substrate-constrained GZO film produced through chemical deposition. Both films exhibited uniform crystal structures and phase purity; however, the substrate-constrained film displayed additional diffraction peaks, suggesting potential substrate interactions. The 3D-printed free-standing film effectively eliminated the tensile stresses observed in the substrate-constrained film. FE-STEM analysis revealed nanostructures with homogeneous elemental distribution in both films, though the substrate-constrained film showed discontinuities, such as pores, likely caused by post-deposition annealing treatment. XPS analysis highlighted differences in chemical states and elemental compositions between the films, influenced by fabrication methods, substrate-induced stresses, and surface energy mismatches. The free-standing GZO film developed through 3D printing exhibited a more balanced incorporation of Zn and O, as it was not subject to substrate or post-deposition annealing constraints. Consequently, it demonstrated a 14 % increase in electrical conductivity and a 91 % improvement in the Seebeck coefficient compared to the substrate-constrained film, resulting in a higher room-temperature power factor of 261 nW/m·K2. These findings underscore the potential of 3D-printed free-standing GZO films to advance thermoelectric applications, offering a promising alternative to overcome the challenges of substrate-constrained films and further drive innovation in the field.

Investigations on full-Heusler alloys Mn2TaAl and Mn2WAl for spintronic and thermoelectric applications

Half-metallic materials are widely used as spintronic devices such as electrodes, magnetic tunnelling junction and giant magnetoresistance etc. In this work, we have systematically investigated the structural stability, Gilbert damping, electronic structure and magnetism together with exchange interactions and Curie temperatures for Mn2TaAl and Mn2WAl alloys. Initially, we estimate their structural stability and offer possible phase synthesis. Subsequently, the Gilbert damping parameters calculated by the linear response theory are used to assess their response speed as spintronic materials. Furthermore, the Mn2TaAl and Mn2WAl are predicted to be half-metallic and nearly half-metallic ferrimagnets, their total magnetic moments obey the Mt=Zt-18 rule. Accordingly, their Curie temperatures for Mn2TaAl and Mn2WAl are also evaluated by the mean-field approximation. Finally, their thermodynamic parameters within 0∼600 K and thermoelectric properties within 200∼900 K are discussed. Overall, our research for Mn2TaAl and Mn2WAl alloys might provide some valuable clues for their application in spintronic devices.