Enhancing Thermoelectric Properties Research Articles

Enhancing thermoelectric properties of spinel ZnFe2O4 by Ni substitution through electron hopping mechanism

The prime goal of this novel work is to investigate the efficacy of spinel zinc ferrite as a thermoelectric material and its performance enhancement for high temperature applications. Zn1-xNixFe2O4 (0 ≤ x ≤ 0.2) were prepared by sol-gel method and their structural, morphological, and thermoelectric behaviours were examined as functions of composition and temperature. Among the studied compositions, Zn0.8Ni0.2Fe2O4 exhibits the highest electrical conductivity (σ) of 49.83 S/m, the largest power factor of 6.66 μW/mK2, and the lowest thermal conductivity (κ) of 0.36 W/mK at 947 K, thus extending to an overall enhancement in the thermoelectric figure of merit (zT). Conduction through electron hopping is proven to be the main driving force for the enhancement in electrical and thus thermoelectric properties. Results reveal that thermoelectric properties of ZnFe2O4 can potentially be enhanced by the doping Ni at Zn site and opens up an exciting opportunity for the utilization of this spinel ferrite as a novel thermoelectric material for applications involving elevated temperatures.

Predicting High‐Performance Thermoelectric Materials With StarryData2

AbstractIn recent years, machine learning (ML) has emerged as a potential tool in the exploration of thermoelectric (TE) materials. This study exploits the StarryData2 public database to construct an ML model for predicting the figure‐of‐merit ZT of TE materials. The original dataset from StarryData2 (372,480 datapoints) underwent systematic cleaning, resulting in a refined dataset of 18,126 instances with 2,761 unique compounds. The cleaned data is employed to train an XGBoost regressor model, utilizing chemical formulas of TE compounds as features to predict ZT at given temperatures. The XGBoost regressor exhibited high prediction accuracy, achieving the coefficient of determination (R2) scores of 0.815 and mean absolute error (MAE) of 0.103 for the test set, further evaluated through cross‐validation across 5 folds. The learning curve analysis demonstrated improved model performance with increased training data. Furthermore, the contributions of different chemical descriptors to ZT are analyzed based on feature importance analysis. Beyond conventional TE families in the training set, the trained model is applied to predict ZT for promising unexplored TE materials and estimate optimal doping concentrations. This comprehensive study shows the impact of ML on TE material research, offering valuable insights and accelerating the discovery of materials with enhanced TE properties.

Oxidation Control to Augment Interfacial Charge Transport in Te-P3HT Hybrid Materials for High Thermoelectric Performance.

Organic-inorganic hybrid thermoelectric (TE) materials have attracted tremendous interest for harvesting waste heat energy. Due to their mechanical flexibility, inorganic-organic hybrid TE materials are considered to be promising candidates for flexible energy harvesting devices. In this work, enhanced TE properties of Tellurium (Te) nanowires (NWs)- poly (3-hexylthiophene-2, 5-diyl) (P3HT) hybrid materials are reported by improving the charge transport at interfacial layer mediated via controlled oxidation. A power factor of ≈9.8µW(mK2)-1 is obtained at room temperature for oxidized P3HT-TeNWs hybrid materials, which increases to ≈64.8µW(mK2)-1 upon control of TeNWs oxidation. This value is sevenfold higher compared to P3HT-TeNWs-based hybrid materials reported in the literature. MD simulation reveals that oxidation-free TeNWs demonstrate better templating for P3HT polymer compared to oxidized TeNWs. The Kang-Snyder model is used to study the charge transport in these hybrid materials. A large σE0 value is obtained which is related to better templating of P3HT on oxygen-free TeNWs. This work provides evidence that oxidation control of TeNWs is critical for better interface-driven charge transport, which enhances the thermoelectric properties of TeNWs-P3HT hybrid materials. This work provides a new avenue to improve the thermoelectric properties of a new class of hybrid thermoelectric materials.

Enhancing thermoelectric properties of higher manganese silicide through facilitated non-equilibrium reactions via the introduction of additional Carbon nano-dots

Higher manganese silicide (HMS) has gained significant attention as a compelling choice for thermoelectric (TE) applications at medium temperatures due to its abundance, environmental friendliness, and impact resistance properties. Recent achievement in HMS involves leveraging the synergistic effect of energy filtering, modulation doping, and boundary scattering to enhance the TE performance. However, excellent TE properties on HMS usually demands extreme preparation processes such as shock compression, melt spinning technique, or chemical vapor transport approach, as well as the use of rare and expensive elements or nano-dots (NDs), such as Re, Ge, Ag/Pt alloy, or CsPbBr3 quantum dots. In this study, a facile wet ball milling combing with spark plasma sintering is used to streamline the synthesis processes. Relatively green, cost-effective, and accessible C NDs are used to facilitated non-equilibrium reactions and enhance TE properties of HMS. Due to the C-doped effect, the PF increased from 1.42 to 1.62 mW m−1 K−2 at 723 K, representing an approximately 14 % improvement compared to the pristine HMS. The introduction of C, derived SiC and Mn NDs result in the enhancing phonon scattering, and leading to a reduction in lattice thermal conductivity from 2.21 to 1.81 W m−1 K−1. Consequently, the figure of merit (zT) increases from 0.42 to 0.55 at 823 K, representing an enhancement of approximately ∼ 31 %. Predictably, the incorporation of C NDs into semiconductors stands as one of the effective strategies for enhancing the TE properties.

Enhancing thermoelectric properties of (Cu,Te) co-doped skutterudite synthesized by solid-state reaction

(Cu,Te) co-doped CoSb3-based thermoelectric compounds Cu0.3Co4Sb12-xTex were synthesized rapidly by solid-state reaction method with the sintering temperature∼923 K and holding time ∼20 min. XRD analysis showed that the prepared samples Cu0.3Co4Sb12-xTex were single-phase skutterudite structure in the range of x < 0.7 %. SEM and EDS analyses show that the sample grains are fine with an average diameter of micro-nanometer and the sample contains many micro-pores inside and the grains have a relatively uniform distribution of elements. The lattice thermal conductivity at high temperature of Cu0.3Co4Sb12-xTex (x = 0,0.3,0.5, 0.7,0.9) significantly reduced by ∼50 % when compared to the samples at room temperature due to enhanced scattering of fine grains, micro porosity and grain boundary. The maximum power factor ∼2824 μWm−1K−2 was obtained for Cu0.3Co4Sb11.5Te0.5 at 769 K and a maximum ZT value of ∼0.83 at 623 K are obtained from (Cu,Te) co-doped CoSb3 material.

First-Principles Study of Doped CdX(X = Te, Se) Compounds: Enhancing Thermoelectric Properties.

Isovalent doping offers a method to enhance the thermoelectric properties of semiconductors, yet its influence on the phonon structure and propagation is often overlooked. Here, we take CdX (X=Te, Se) compounds as an example to study the role of isovalent doping in thermoelectrics by first-principles calculations in combination with the Boltzmann transport theory. The electronic and phononic properties of Cd8Se8, Cd8Se7Te, Cd8Te8, and Cd8Te7Se are compared. The results suggest that isovalent doping with CdX significantly improves the thermoelectric performance. Due to the similar properties of Se and Te atoms, the electronic properties remain unaffected. Moreover, doping enhances anharmonic phonon scattering, leading to a reduction in lattice thermal conductivity. Our results show that optimized p-type(n-type) ZT values can reach 3.13 (1.33) and 2.51 (1.21) for Cd8Te7Se and Cd8Se7Te at 900 K, respectively. This research illuminates the potential benefits of strategically employing isovalent doping to enhance the thermoelectric properties of CdX compounds.

Exploiting synergies for high thermoelectric performance in higher manganese silicide-based semiconductors through element Co-doping, energy filtering, and phonon scattering

Higher manganese silicide (HMS) is a promising thermoelectric (TE) semiconductor that operates effectively at medium temperatures. It is characterized by its abundance, environmental friendliness, and desirable impact resistance properties. To enhance the TE properties of HMS, this study employs isoelectronic anion and cation codoping, combined with embedded quantum dot (QD) techniques. The introduction of element doping and nanoinclusions, such as Mn0.96Re0.04(Si0.96Ge0.04)1.79+1.5%Ag2Pt QDs sample, leads to an approximately 85% increase in electrical conductivity. This boost is attributed to the adjustment of the band structure through Re, Ge, and Ag element doping and the charge transfer facilitated by MnSi, Si, and Pt precipitates. Furthermore, the enhanced PF of 1.85 × 10−3 W m−1 K−2 at 773 K is approximately 29% higher than that of pure HMS. Simultaneously, the increase in point defects hampers the improvement of lattice thermal conductivity (κl) by intensively scattering short-wave phonons. This effect is complemented by the precipitation of Si, MnSi, Ag, and Pt nanoparticles, which increases the density of grain boundaries, enhances medium-wave phonon scattering, and substantially reduces κl to 1.45 W m–l K−1 (at 773 K), ∼30% lower than that of pure HMS. The figure of merit of the sample containing 1.5%Ag2Pt QDs at 823 K attains a value of 0.69, which is ∼52% and ∼19% higher than that of pure HMS and Re-Ge-double-doped samples, respectively. The incorporation of isoelectronic codoping, along with the integration of metastable QDs, is demonstrated as an effective strategy for enhancing TE properties.

Self-doping enhancing thermoelectric properties of GeTe thin films

The thermoelectric film has broad application potential in the self-power supply of miniature electrical equipment. In this work, GeTe thermoelectric films were prepared using physical vapor deposition combined with annealing processes. Benefitting from the high mobility enabled by the increased crystallinity and the optimized carrier concentration via Ge self-doping, the power factor of a GeTe thin film was significantly improved to 18 μW cm−1 K−2 (300 K), and the maximum one (28 μW cm−1 K−2) was achieved at 576 K. Furthermore, thermoelectric thin film devices assembled with high-performance GeTe films exhibited superior output performance at a temperature difference of 40 K. The maximum open circuit voltage reached 12.2 mV and the power density was 2.4 mW cm−2, indicating that GeTe thin films have broad application prospects in the field of self-power supply.

Enhancing thermoelectric properties of Ca3Co4O9 ceramics through oscillatory pressure sintering

Oscillatory Pressure Sintering (OPS) has been demonstrated to be a favorable manufacturing approach for the control of fine and uniform distribution of grains in various ceramic systems, which can lead to enhanced densification and thus improved physical and mechanical properties. In this study, OPS was utilized to prepare pure Ca3Co4O9 thermoelectric material. The results show that the electrical properties and thermoelectric properties of Ca3Co4O9 prepared by OPS are superior to those of samples sintered by conventional hot pressing (HP) without oscillation. This may be attributed to the better alignment of plate-like grains in the OPS samples, which increase electrical conductivity, and also the higher density of grain boundaries that enhance the phonon scattering and, thus, the reduction of thermal conductivity. This study suggests that a straightforward oscillatory pressure sintering approach can be utilized to obtain high-quality and high-performance thermoelectric materials without the need for doping, templating, or high-temperature sintering.

Enhancing thermoelectric properties of Bi2Te3 film via CuI doping: Sputtering and solid iodination methods verified by ab initio calculation

We have introduced an innovative method for preparing CuI-doped Bi2Te3 films for the first time, which was also validated through ab initio calculations. The chemical reaction between the Cu-Bi2Te3 film and iodine was conducted using the solid iodination method at room temperature. The results from X-ray diffraction and energy-dispersive spectrometry suggest that the sputtering process, followed by the solid iodination method, holds promise for synthesizing CuI-doped Bi2Te3 films. Additionally, appropriately doping Bi2Te3 with CuI enhances the (00l) crystal orientation, increases carrier concentration and mobility, resulting in improved electrical conductivity. Furthermore, our calculation results align with our experimental findings. An excess of substitutional CuI dopant tends to generate secondary phases, leading to alterations in the intrinsic conductivity and a reduction in the thermoelectric properties of Bi2Te3. Leveraging the enhanced electrical transport properties achieved through CuI doping, the maximum power factor of the (CuI)0.2Bi2Te2.9 film reaches approximately 2.40 × 10−3 W/mK2 at 423 K, representing a 66 % enhancement compared to that of the Bi2Te2.9 film, which has a power factor of 1.44 × 10−3 W/mK2.

Structural, electronic, optical, and thermoelectric properties of CsPbI3-yBry (y = 0.5, 1.5, 2.5) compounds: First-principle study

BackgroundAmong photovoltaic materials, halide-based perovskites, such as CsPbI3, have been the subject of many research papers due to their suitable and direct bandgap, very good optical properties, and remarkable thermoelectric properties. Enhancing optoelectronic and thermoelectric properties can be achieved by combining halide atoms intelligently. The purpose of this article is to examine the physical properties of Br substitution at different concentrations in CsPbI3 perovskite. MethodsThe structural, electrical, and optical properties of CsPbI3-yBry (y = 0.5, 1.5, 2.5) compounds have been investigated by using the QUANTUM-ESPRESSO/PWSCF computational package which is based on the density functional theory and the pseudo-potential technique. The thermoelectric properties of CsPbI3-yBry perovskites were calculated by solving the Boltzmann transport equations within the constant relaxation time approximation as employed in the BoltzTraP package. Significant findingsThe structural investigation reveals that when the I atom is substituted by Br, the lattice constant decreases, increasing the bulk modulus and stiffness of compounds. The calculated negative formation energy confirmed the thermodynamic stability of CsPbI3-yBry compounds, and the stability improved with an increase in Br concentration. The electronic investigation indicates the semiconductor nature of compounds with a direct band gap, with a slight increase in electronic band gap as Br concentration increases. The noticeable optical absorption coefficient in the visible range of the electromagnetic spectrum, along with high and tunable optical conductivity, confirms the capability of the compounds for use in optoelectronic devices. The positive value of the Seebeck coefficient revealed the p-type semiconducting nature of CsPbI3-yBry perovskites. Lattice thermal conductivity calculation reveals that this quantity is decreased because of the increase in phonon-phonon interaction due to rising temperature. Thermoelectric investigation indicates that a precise mixture of halide I and Br atoms significantly enhances the electrical and thermal conductivity of perovskites. Also, the substitution of halide I atoms by Br can improve the figure of merit (ZT). The maximum value of ZT at room temperature is equal to 0.99, justifying the brilliant thermoelectric properties of the studied compounds.

Improved thermoelectric properties of Sb-doped Ti0.5Zr0.5NiSn alloy with refined structure induced by rapid synthesis processes

Thanks to the great advantage of preparation methods, the thermoelectric (TE) alloy materials can be fast synthesized with controllable structural morphology for optimizing charge and phonon transport properties, thereby improving the TE efficiency of the material. Herein, a series of Sb-doped Ti0.5Zr0.5NiSn1−xSbx based half-Heusler alloy was prepared via a combined fast procedure of arc melting (AC), melt spinning (MS) followed by spark plasma sintering (SPS). The detailed analyses of morphology, phase structure, and composition reveal high-quality samples through processes for enhanced TE properties. High ZT values over one are achieved for all samples with slight Sb doping content variation from x = 0.0025–0.02. The enhanced TE performance of the Sb-doped Ti0.5Zr0.5NiSn1−xSbx alloys here results from the synergistic between the approaches such as doping, alloying, nanostructuring, and the presence of nano-precipitates induced by MS. The highest ZT values of ∼1.2 at 847 K with an average ZT of 0.798 and estimated TE conversion efficiency reached 12.8% in the temperature range from 300 K to 847 K were achieved for the 1.25% Sb doped sample. In addition, the thermal cycling test through continuous measurement of five and a half cycles confirmed the high thermal stability of the bulk alloy. High ZT and thermal stability based on Hf-free Ti0.5Zr0.5NiSn1−xSbx alloy and fast synthesis are well matched for commercial requirements.

Enhancing thermoelectric properties of AgSbTe2 thin films by modulating vacancies and microstructures

Thin-film thermoelectrics (TE) are of significance for micro-TE coolers and generators. AgSbTe2 is attracting extensive attention due to the ultra-low thermal conductivity and large Seebeck coefficient, but the TE performance of AgSbTe2 film is still not satisfactory. Herein, oriented Cd-doped AgSbTe2 films have been prepared by magnetron sputtering. Tuning the annealing temperature can change the concentration of vacancies and grain size of the AgSbTe2 film, leading to enhanced electrical conductivity and power factor. Due to the effective scattering induced by the nanostructure and grain boundaries, the thermal conductivity of the AgSbTe2-based thin films is also significantly reduced. As a result, the figure of merit zT can reach 1.38 at 523 K, and the average zT reaches 0.91 in the temperature range from 300 to 523 K. Our work demonstrates that the modulation of vacancies and microstructures is a feasible way to enhance the TE performance of the AgSbTe2-based films.

Enhancing thermoelectric properties of CuNiO thin films through post-annealing: Effect on Seebeck coefficient and power generation

The need for the best thermoelectric power generation to extract low-grade heat energy from the human body has generated considerable interest. However, developing oxide-based thermoelectric materials with both high stability and Seebeck coefficient remains challenging. In this work, we have prepared CuNiO thin film with an economical and simple thermal evaporation method and post-annealed at different temperatures from 400 to 550 °C. XRD and SEM have determined the crystal structure and surface morphology of the CuNiO thin film. The electrical conductivity and charge carrier concentration increase with post-annealing temperature due to the formation of the secondary phases. The Seebeck coefficient has decreased from 65.1 to 37.9 µV/K with post-annealing temperature due to improved charge carrier density, the electronic band structure of the material and secondary phases. The maximum power factor has been achieved in the unannealed sample.

Enhancing thermoelectric properties of MCoSb-based alloys by entropy-driven energy-filtering effects and band engineering

MCoSb-based medium-entropy half-Heusler (HH) alloy with low lattice thermal conductivity (κL) is a promising medium- and high-temperature thermoelectric material. However, the unexpected band structure of the alloy leads to a sudden decrease in the Seebeck coefficient (S), which severely restricts the optimization of the figure-of-merit (ZT). In this study, we demonstrate a new concept for decoupling S and electrical conductivity (σ) based on entropy engineering. This method involves band engineering and the energy-filtering effect, where the entropy-driven quantum confinement effect is manipulated to filter low-energy electrons, and the increasing entropy promotes a rapidly changing density of state near Fermi level. Consequently, an excellent S of ∼ −211.6 μV K−1 at 923 K was achieved for the M0.82Nb0.18CoSb HH alloy, which is 62.3% higher than that of the pristine M0.85N0.15CoSb (M = Ti, Zr, Hf; N= V, Ta; equimolar) HH alloy (∼−130.4 μV K−1). Moreover, benefiting from the optimization of S and κL, a peak ZT was enhanced from ∼0.17 for the pristine M0.85N0.15CoSb medium-entropy HH alloy to 0.58 for the M0.85Nb0.15CoSb high-entropy HH alloy. These results broaden the applications of entropy-engineering to decrease κL and decoupling between S and σ.

Advancement of Polyaniline/Carbon Nanotubes Based Thermoelectric Composites.

Organic thermoelectric (TE) materials have been widely investigated due to their good stability, easy synthesis, and high electrical conductivity. Among them, polyaniline/carbon nanotubes (PANI/CNTs) composites have attracted significant attention for pursuing enhanced TE properties to meet the demands of commercial applications. In this review, we summarize recent advances in versatile PANI/CNTs composites in terms of the dispersion methods of CNTs (such as the addition of surfactants, mechanical grinding, and CNT functional group modification methods), fabrication engineering (physical blending and in-situ polymerization), post-treatments (solvent treatments to regulate the doping level and microstructure of PANI), and multi-components composites (incorporation of other components to enhance energy filtering effect and Seebeck coefficient), respectively. Various approaches are comprehensively discussed to illustrate the microstructure modulation and conduction mechanism within PANI/CNTs composites. Furthermore, we briefly give an outlook on the challenges of the PANI/CNTs composites for achieving high performance and hope to pave a way for future development of high-performance PANI/CNTs composites for sustainable energy utilization.

Enhancing thermoelectric properties of p-type (Bi,Sb)2Te3 via porous structures

Bismuth telluride is a widely used commercial thermoelectric material with excellent thermoelectric performances near room temperature. Reducing thermal conductivity is one of the most effective ways to improve performances of thermoelectric materials. In this study, the thermal conductivity of the material was reduced by fabricating porous structures. Highly dense NaCl-(Bi,Sb)2Te3 composites were fabricated by a high-pressure technology. The NaCl phase was then removed from the composites by ultrasonic washing to produce porous structures. The produced (Bi,Sb)2Te3 porous materials possessed excellent thermoelectric properties. The porosity and pore size of the (Bi,Sb)2Te3 porous materials increased with the increasing NaCl content, decreasing the thermal conductivity significantly. An ultra-low lattice thermal conductivity of 0.21 Wm−1K−1 at 493 K was achieved when the porosity was 39%, almost the lowest lattice thermal conductivity reported for (Bi,Sb)2Te3 bulk materials. The figure of merit ZT value was enhanced to 1.05 at 493 K when the porosity was 25%. Compared with the most compacted samples (ZT = 0.79 and porosity of 10%) prepared under the same conditions, the ZT value of the porous samples increased by 33%. This study indicated that porous thermoelectric materials can be prepared simply, quickly and efficiently by high-pressure/ultrasonication washing to improve thermoelectric performances, which has evident reference values for preparing other thermoelectric pore materials with enhancing behaviors.

Effects of Bi and Sb doping on the thermoelectric performance of n-type quaternary Mg2.18Ge0.1Si0.3Sn0.6 materials

Mg2.18(Si0.3Ge0.1Sn0.6)1-yXy (X ​= ​Bi, Sb; y ​= ​0, 0.02, 0.06) quaternary solid solutions were synthesized via solid state reaction after ball milling followed by hot-pressing. The influences of Bi and Sb doping on its thermoelectric (TE) properties, such as thermal conductivity, Seebeck coefficient, and electrical conductivity were discussed in the temperature range of 300–800 ​K. Our results show that Bi and Sb are effective in n-type doping. The results illustrate that the Seebeck coefficient decreases, whereas electrical conductivity increases with increasing temperature for undoped compositions. However, the electrical conductivity decreases in a metal-like behavior for the doped sample. Additionally, the samples doped with Bi0.02 and Sb0.02 show enhanced TE properties as compared to those doped with Bi0.06 and Sb0.06, respectively. A maximum ZT of 1.28 is achieved in the sample doped with Sb0.02.

Enhancing thermoelectric properties of isotope graphene nanoribbons via machine learning guided manipulation of disordered antidots and interfaces

Structural manipulation at the nanoscale breaks the intrinsic correlations among different energy carrier transport properties, achieving high thermoelectric performance. However, the coupled multifunctional (phonon and electron) transport in the design of nanomaterials makes the optimization of thermoelectric properties challenging. Machine learning brings convenience to the design of nanostructures with large degree of freedom. Herein, we conducted comprehensive thermoelectric optimization of isotopic armchair graphene nanoribbons (AGNRs) with antidots and interfaces by combining Green's function approach with machine learning algorithms. The optimal AGNR with ZT of 0.894 by manipulating antidots was obtained at the interfaces of the aperiodic isotope superlattices, which is 5.69 times larger than that of the pristine structure. The proposed optimal structure via machine learning provides physical insights that the carbon-13 atoms tend to form a continuous interface barrier perpendicular to the carrier transport direction to suppress the propagation of phonons through isotope AGNRs. The antidot effect is more effective than isotope substitution in improving the thermoelectric properties of AGNRs. The proposed approach coupling energy carrier transport property analysis with machine learning algorithms offers highly efficient guidance on enhancing the thermoelectric properties of low-dimensional nanomaterials, as well as to explore and gain non-intuitive physical insights.

Aqueous Synthesis, Doping, and Processing of n-Type Ag2Se for High Thermoelectric Performance at Near-Room-Temperature.

Herein, we have successfully synthesized binary Ag2Se, composite Ag0:Ag2Se, and ternary Cu+:Ag2Se through an ambient aqueous-solution-based approach in a one-pot reaction at room temperature and atmospheric pressure without involving high-temperature heating, multiple-processes treatment, and organic solvents/surfactants. Effective controllability over phases and compositions/components are demonstrated with feasibility for large-scale production through an exquisite alteration in reaction parameters especially pH for enhancing and understanding thermoelectric properties. Thermoelectric ZT reaches 0.8-1.1 at near-room-temperature for n-type Ag2Se and Cu+ doping further improves to 0.9-1.2 over a temperature range of 300-393 K, which is the largest compared to that reported by wet chemistry methods. This improvement is related to the enhanced electrical conductivity and the suppressed thermal conductivity due to the incorporation of Cu+ into the lattice of Ag2Se at very low concentrations (x%Cu+:Ag2Se, x = 1.0, 1.5, and 2.0).