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Highlights • Cost effective and scalable strategy for the development of high performance nanostructured thermoelectric bulk materials. • Substantial enhancement is observed in electrical conductivity and Seebeck coefficient. • Significantly improved thermoelectric figure of merit of the composite from the pristine bulk sample. Abstract Graphene in different vol% ranging from 0.5, 0.75 and 1.5 were uniformly incorporated in the nanostructured Bi 2 Te 3 that was obtained from ball milling the coarse powder. The composite and the pristine Bi 2 Te 3 powders were consolidated by the high frequency induction heated sintering. The thermoelectric properties of the bulks were investigated in the temperature range from 300 to 525 K. The effective thermal conductivities of the composites decrease with the reduction in the particle size of the pristine Bi 2 Te 3 as well as with the addition of graphene attributed to enhanced phonon scattering from the phase boundaries. The significant increase in electrical conductivity accompanied by less decrease in the Seebeck coefficient at 1.5 vol% of graphene culminates in a high power factor. The results suggest that enhancement in power factor is attributed to quantum confinement effect through introduction of 2D graphene in Bi 2 Te 3. Thus, reduction in thermal conductivity in conjunction with substantial improvement in power factor at 1.5 vol% of graphene leads to considerable enhancement in the thermoelectric figure of merit at ∼500 K from pristine bulk. This work presents a novel strategy for development of high performance cost effective and scalable nanostructured thermoelectric bulk materials similar to Bi 2 Te 3 based superlattices. [ABSTRACT FROM AUTHOR]

CuInX 2 (X = S, Se and Te) are members of Cu-based compounds with diamond-like structures. Their bonding characteristics, electronic structure and thermoelectric properties are studied using first-principles methods and the semiclassical Boltzmann theory. Due to the Cu-3d orbits in CuInX 2 , we use the mBJ + U method to obtain the accurate band gap and electronic structures. The analysis of the electronic structure for CuInX 2 indicates that the combination of heavy and light bands near the Fermi level is conductive to achieve high thermoelectric performances. However, few literatures have reported the reason of the combination. Further study on AgGaTe 2 , CuGaTe 2 , and CuInX 2 (X = S, Se and Te) shows that the stronger interaction between Cu-Te atoms leads to the combination of heavy and light bands in Cu-based compounds. These results provide a valuable theoretical guidance that the introduction of Cu-Te bonding in experimental synthesis is helpful to improve the thermoelectric properties. [ABSTRACT FROM AUTHOR]

This study reports on photoelectrical performance of the long-wave infrared HgCdTe high operating temperature (200-230 K) detector for the fast response time operating under unbiased conditions. The detailed analysis of the response time as a function of device architecture was conducted pointing out optimal working conditions and structure. The response time of the long-wave (xCd = 0.19) HgCdTe detector for temperatures reached by thermoelectrical cooling (200-230 K) was estimated at the level of τs < 0.6 ns for unbiased condition while responsivity Ri ~ 1.8 A/W and detectivity was assessed at the level of D* ~ 1.6 × 1010 cm Hz½/W. It was shown that extra series resistance Rseries < 10 Ω (resistance-capacitance time constant) plays a decisive role in order to reach τs < 1 ns meaning that device processing is much more important rather than fundamental limitations imposed by physics. [ABSTRACT FROM AUTHOR]

Lead-free Ba (1-x) Sr x TiO 3 (BST) ceramics were fabricated to convert near-room-temperature waste heat to electric energy for creating self-powered and ‘battery-less’ systems. In comparison to thermoelectrics that are specifically used for harvesting heat with stable temperature span, pyroelectric converters based on Olsen cycle mechanism can harvest heat with temperature-vibration environment. Large energy conversion density ( N D ) was obtained in BST ceramics within the narrower temperature gradient (< 60 °C). In terms of the diffused phase transition (DPT) in BST ceramics, the extra slim hysteresis loops processed relatively low coercive field ( E c ) and hysteresis loss, which can effectively enhance the N D owing to the wider electrical field interval. The effect of Curie temperature ( T c ) tuned by the ratios of Ba/Sr on N D and applicable range of temperature were also systematically examined. At the same electrical field difference (07 MV/m), the optimal energy conversion properties were gained around the T c , e.g., 0.36 J/cm 3 for BST66/ 3 4 ( T c = 23 °C) within a temperature range between 25 °C and 65 °C, and 0.48 J/cm 3 for BST72/28 ( T c = 43 °C) between 25 °C and 85 °C. [ABSTRACT FROM AUTHOR]

Recently, many novel superionic thermoelectric materials have been discovered along the concept of “phonon-liquid electron-crystal” (PLEC). Among them, Cu 2- x Se-based liquid-like materials are typical examples. In this study, a series of copper-deficient Cu 2- x Se (0.05 ≤ x ≤ 0.25) materials were synthesized and used to study the role of Cu vacancies on the electrical and thermal transport properties. The X-ray photoelectron spectroscopy (XPS) measurements suggest that the valence states of Cu and Se are independent on the Cu/Se atomic ratio. With increasing the content of Cu vacancies, the hole concentration is monotonously increased, leading to the improved electrical conductivity and reduced Seebeck coefficient. Based on the single parabolic band model analysis, it is found that changing the content of Cu vacancies does not obviously modify the material's electronic band structure and effective mass. Due to the presence of highly mobile Cu ions inside the crystal structure, the lattice thermal conductivities of all Cu 2- x Se (0.05 ≤ x ≤ 0.25) materials are very low with values around 0.39 W m −1 K −1 at 500 K. Because of the significantly reduced Seebeck coefficient and increased electronic thermal conductivity, the thermoelectric figure of merit zTs are decreased when increasing x from 0.05 to 0.25. At 750 K, a maximum zT of 0.46 is obtained in Cu 1.95 Se among all Cu 2- x Se (0.05 ≤ x ≤ 0.25) materials. [ABSTRACT FROM AUTHOR]

The low surface-charge stability of polypropylene (PP) frequently limits its application as an electret material. In this paper, we demonstrate how the treatment of PP-film surfaces with orthophosphoric acid (H3PO4) enhances their charge stability. To discriminate between the effects of chemical modification and thermal treatment, as-received and annealed PP films are used as reference samples. The electret properties of treated and non-treated PP films are characterized with thermally stimulated discharge (TSD) and isothermal surface-potential decay (ISPD) experiments, from which considerable improvement in thermal and temporal charge stability is observed for samples modified with H3PO4. The half-value temperature (T1/2) observed on TSD curves of chemically treated PP increases to 131 and 145 °C for positive and negative charges, respectively. The enhancement might be attributed to the phosphoric compounds detected on the H3PO4-modified surfaces via attenuated-total-reflection infrared spectroscopy. Deeper surface traps formed at the "foreign" phosphorus-containing structures are able to capture the charges over longer time periods and at higher temperatures, thus leading to significant improvements in the temporal and thermal surface-charge stabilities of PP electrets. [ABSTRACT FROM AUTHOR]

Cu 10.5 Zn 1.5 Sb 4 S 13 tetrahedrite compound was prepared by mechanical milling of Cu 2 S, ZnS and Sb 2 S 3 powders and spark plasma sintered (SPS) to dense samples. The phase formation, chemical homogeneity, thermal stability of the compound and the thermoelectric properties of the sintered samples were evaluated. Single phase tetrahedrite with the crystallite size of 40 nm was obtained after 30 h of milling followed by annealing at 573 K for 6 h in an argon atmosphere. In-situ high-temperature X-ray diffraction studies revealed that the phase is stable up to 773 K. The Seebeck coefficient of the sintered samples of density >98% shows p-type behavior with maximum thermopower of 170 μV/K at 573 K. The electrical resistivity (ρ) decreases with temperature up to 475 K and then increases. A low thermal conductivity of 0.5 W/(m⋅K), in combination with moderate power factor gave a maximum ZT of ∼0.038 at 573 K in Cu 10.5 Zn 1.5 Sb 4 S 13 sample having a grain size of ∼200 nm. [ABSTRACT FROM AUTHOR]

Platelet crystals based on Ruddlesden–Popper (RP) polytypes prepared by molten-salt synthesis were used to influence the microstructural development of Nb-doped SrTiO 3 (STO;Nb) perovskite and, consequently, to change the thermoelectric properties. Electron microscopy revealed intergrowth of RP-polytypic phases within the STO;Nb solid-solution matrix phase. The morphology of the grains varied from isotropic to anisotropic, containing polytypic faults up to 100 μm in length. Such a microstructure increased the thermoelectric figure of merit by 50% at 650 °C, due to substantially enhanced electrical conductivity, slightly increased Seebeck coefficient and lowered thermal conductivity. [ABSTRACT FROM AUTHOR]

Low temperature thermoelectric (TE) materials are in demand for more efficient cooling and power generation applications. Iron antimonide (FeSb2) draws great attention over the past few years because of its enhanced power factor values. Polycrystalline bulk FeSb2 nanopowder was prepared via a low-temperature molten salts approach followed by subsequent thermal treatment in synthetic air and hydrogen gas for calcination and reduction reactions, respectively. Structural analysis confirms the desired final phase with submicrometer grain size and high compaction density after consolidation using spark plasma sintering (SPS). TE transport properties revealed that the material is n-type below 150 K and p-type above this temperature; this suggests antimony vacancies in FeSb2. The electrical conductivity increased significantly, and the highest conductivity achieved was 6000 S/cm at 100 K. The maximum figure-of-merit, ZT, of 0.04 is achieved at 500 K, which is about 6 times higher than the earlier reported state-of-the art ZT value for the same material. [ABSTRACT FROM AUTHOR]

The purpose of this work is to describe, with numerical simulation, the space charge behavior in polymeric materials. Particular intent is accorded to the variation of the thermo-electrical constraints. The simulation is performed for a range of the electric field from 10 to 110 MV/m and the space charge behavior was described at various temperatures: 0, 27, 60 and 100 ° C. In general, the numerical results show a predominance of the temperature effect, vs. the electric field, on the space charge behavior. The dynamic of the electrical charges is different under 100 ° C, a forehead is observed on their distribution in the sample. Strong electric field enhancements are remarked in the dielectric, they exceed 38% of the applied field under 100 ° C. Only 1.3% of augmentations are observed under room temperature even with higher applied field of 110 MV/m. Both experimental and theoretical Current-Field characteristics, plotted in log-log scale, show linear behavior with slopes greater than one. The different values of slope indicate space charge limited conduction; a change is remarked at 40 MV/m which can defines the beginning of the high fields regime in the case of the studied polymer (Polyethylene Naphthalate). [ABSTRACT FROM PUBLISHER]

The effect of Si 4 + content on the microstructure and thermoelectric properties of Sr 1 − x Si x MnO 3 − δ (0.05 ≤ x ≤ 0.3) samples is discussed. For x ≤ 0.15, the substitution of Si 4 + for Sr 2 + leads to a significant increase in electrical conductivity and a decrease in the absolute value of the Seebeck coefficient due to an increase in electron concentration. For 0.2 ≤ x ≤ 0.3, the substituted Si 4 + lowers the electrical conductivity. This is mainly attributed to decreases in the density and grain size as well as to the formation of secondary phases, such as Mn 3 O 4 , Mn 2 O 3 , and Sr 2 SiO 4 , resulting in a decrease in electron mobility. The substituted Si 4 + reduces the thermal conductivity due to increased phonon scattering. The maximum dimensionless figure-of-merit ( ZT ) obtained in this study is 0.041 at 800 °C for x = 0.15. The partial substitution of Si 4 + for Sr 2 + in SrMnO 3 − δ yields a significant improvement in the thermoelectric properties. [ABSTRACT FROM AUTHOR]

Performance of temperature control is crucial to the operation of isoelectric focusing equipment (IEF). In this paper, two-stage thermoelectric cooling module (TEM) is proposed to be adopted in IEF to realize prompt and precise temperature control as well as low focusing temperature (T f ). Three different prototypes including HP + baffle , AL + baffle and HP + fin are developed to obtain optimal design. Experimental setups of these prototypes are built up to test their performance. Temperature distribution on cooling plate, COP and air temperature in bottom chamber with respect to different T f s are adopted as performance indices to evaluate performance of these prototypes. Experimental results show that aluminum plate with heat pipes, used as cooling plate, can improve its temperature uniformity. Moreover, fin-type heat sink with baffle can effectively dissipate heat on the hot side of TEM with little impact on the other parts of IEF. The T f of HP + baffle can be kept at 10 °C. And its COP can reach 2.0 under general working condition. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) metal oxides overcome crucial disadvantages of traditional heavy-metal-alloy-based TE materials, such as toxicity, scarcity, and instability at high temperatures. Here, we report the TE properties of metal oxide superlattices, composed from alternating layers of 5% Pr3+-doped SrTiO3−δ (SPTO) and 20% Nb5+-doped SrTiO3−δ (STNO) fabricated using pulsed laser deposition (PLD). Excellent stability is established for these superlattices by maintaining the crystal structure and reproducing the TE properties after long-time (20 h) annealing at high temperature (1000 K). The introduction of oxygen vacancies as well as extrinsic dopants (Pr3+ and Nb5+), with different masses and ionic radii, at different lattice sites in SPTO and STNO layers, respectively, results in a substantial reduction of thermal conductivity via scattering a wider range of phonon spectrum without limiting the electrical transport and thermopower, leading to an enhancement in the figure-of-merit (ZT). The superlattice composed of 20 SPTO/STNO pairs, 8 unit cells of each layer, exhibits a ZT value of 0.46 at 1000 K, which is the highest among SrTiO3-based thermoelectrics. [ABSTRACT FROM AUTHOR]

Highly dispersed olive-like NiS particles were synthesized in a liquid-liquid biphasic system at room temperature, where nickel xanthate in organic solvents (toluene and benzene) and sodium sulfide in water solution were used as nickel and sulfide sources, respectively. NiS particles were formed at the stabilized phase interface. The structures, chemical composition and optical characteristics of the products were investigated by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The organic solvents obviously influenced the morphology of the NiS particles. The olive-like NiS with smooth surface and sharp ends was obtained at benzene/water interface, while spindle-like NiS particles with rough surface and circle ends were formed when using toluene as a solvent. Analogously, chainlike Bi2S3 nanowires were produced at chloroform/water interface. The effect of the experiment parameters including reaction time, solvent and concentration of reactants on the size and morphology of the products was discussed in detail and a possible formation mechanism was suggested. [ABSTRACT FROM AUTHOR]

During the last decade thermoelectrics have emerged as a promising alternative amongst other green power production technologies due to the unique advantages they present. In this respect, performance prediction of thermoelectric devices is critical both for evaluating the potential application of new materials and defining the crucial design parameters of thermoelectric generators and systems. This paper investigates, computationally as well as experimentally, the performance of a commercially available Seebeck module under steady-state operating conditions. Computational results, retrieved using ANSYS Workbench (v. 14.0), were compared to performance data available by the manufacturer. Additionally to that, in order to further verify the integrity of the modelling procedure, experimental evaluation using the same commercial module was conducted in laboratory environment. Although a relatively large deviation between computational and manufacturer data was observed when the mean operating temperature of the generator was taken into account, a very good agreement was established in terms of generator efficiency, providing also a rational explanation to the resulting divergence of the first case. Furthermore, the outcomes of the experimental analysis validated the accuracy of the finite element modelling process. [ABSTRACT FROM AUTHOR]

Electretic state and radiation absorption of nanocomposites consisting of polymer matrix and metal particles filler obtained in result of electric explosion are investigated. Stable thermoelectrets of polymer metal-filled systems that have better electert properties than traditional polymer materials are obtained. Suggested method of composite polymer system creation enables to obtain shielded materials with better radiative absorption, resistant to external actions, cost-efficient. [ABSTRACT FROM AUTHOR]

The production of materials based on mixtures of three different resins and the application of the obtained materials as electrets are proposed. [ABSTRACT FROM AUTHOR]

The present work deals with transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermally stimulated discharge current (TSDC) study of inorganic metal oxide (ZnO) nanoparticles and its thermoelectrets. The thermoelectrets were prepared by applying different electric polarizing field ( E) at constant polarizing temperature ( T), for constant polarization time ( t). The TSDC study was carried out in the temperature region of 313-473 K. It was observed that the conductivity of ZnO samples increases with the increase in temperature and polarizing field. The dependence of TSDC data on polarizing agents, i.e. field and temperature shows Arrhenius type of behviour and is explained on the basis of variable range hopping mechanism. [ABSTRACT FROM AUTHOR]

Abstract: We study the spin-dependent thermoelectric transport through two-dimensional normal/ferromagnetic/normal/ferromagnetic/normal graphene (NG/FG/NG/FG/NG) junctions. It is found that both charge and spin thermopowers depend on the FGʼs magnetization direction and exhibit an anisotropic behavior. Interestingly, the spin thermopower can be as large as the charge thermopower and even can exceed the latter in magnitude. Moreover, the pure spin thermopower and spin current emerge in this device. The results obtained here suggest a feasible way of enhancing thermospin effects and generating the pure spin current in two-dimensional graphene. [Copyright &y& Elsevier]

Irradiation of He-Ne LASER beam on polystyrene (PS) and poly vinyl chloride (PVC) polyblend sample for different time intervals viz. 3, 5,7, 10 and 15 min. Structural and electrical properties have been studied before and after irradiation. It has been found that irradiation increases the dc electrical conductivity due to creation of new charge carriers in the polyblend sample. [ABSTRACT FROM AUTHOR]

This paper describes the results of thermally stimulated discharge conductivity study of activated charcoal-polyvinyl chloride (PVC) thin film thermoelectrets. TSDC has been carried out in the temperature range 308-400°K and at four different polarizing fields. Results are discussed on the basis of mobility of activated charcoal and polyvinyl chloride chains. [ABSTRACT FROM AUTHOR]

In this paper we have investigated thermoelectric effect in the epitaxial graphene on a semiconductor substrate using a simple model. We have obtained the expressions for static conductance and thermopower of the epitaxial graphene. The thermopower of the epitaxial graphene can be abnormally large near the edges of the semiconductor band gap. [ABSTRACT FROM AUTHOR]

Nanocomposite is proved to be an effective method to improve thermoelectric performance. In the present study, graphene is introduced into p-type skutterudite La0.8Ti0.1Ga0.1Fe3CoSb12 by plasma-enhanced chemical vapor deposition (PECVD) method to form skutterudite/graphene nanocomposites. It is demonstrated that the graphene has no obvious effect on the electrical conductivity of La0.8Ti0.1Ga0.1Fe3CoSb12, but the Seebeck coefficient is slightly improved at high temperature, thereby leading to high power factor. Furthermore, due to the enhancement of phonon scattering by the graphene, the lattice thermal conductivity is reduced significantly. Ultimately, the maximum zT value of La0.8Ti0.1Ga0.1Fe3CoSb12/graphene is higher than that of graphene-free alloy and reaches to 1.0 at 723 K. Such an approach raised by us enriches prospects for future practical application. [ABSTRACT FROM AUTHOR]

Binary Cu-based chalcogenide thermoelectric materials have attracted a great deal of attention due to their outstanding physical properties and fascinating phase sequence. However, the relatively low figure of merit zT restricts their practical applications in power generation. A general approach to enhancing zT value is to produce nanostructured grains, while one disadvantage of such a method is the expansion of grain size in heating-up process. Here, we report a prominent improvement of zT in Cu2Te0.2Se0.8, which is several times larger than that of the matrix. This significant enhancement in thermoelectric performance is attributed to the formation of abundant porosity via cold press. These pores with nano- to micrometer size can manipulate phonon transport simultaneously, resulting in an apparent suppression of thermal conductivity. Moreover, the Se substitution triggers a rapid promotion of power factor, which compensates for the reduction of electrical properties due to carriers scattering by pores. Our strategy of porosity engineering by phonon scattering can also be highly applicable in enhancing the performances of other thermoelectric systems. [ABSTRACT FROM AUTHOR]

We report the synthesis of Nd-filled and Fe substituted p-type NdxFe3.2Co0.8Sb12 (x = 0.5, 0.6, 0.7, 0.8, and 0.9) skutterudites by the solid-state reaction method. The influences of Nd filler on the electrical and thermal transport properties are investigated in a temperature range from room temperature to 850 K. A lowest lattice thermal conductivity of is obtained in Nd0.8Fe3.2Co0.8Sb12 at 673 K, which results from the localized vibration modes of fillers and the increase of grains boundaries. Meanwhile, the maximum power factor is for the Nd0.9Fe3.2Co0.8Sb12 sample at 668 K. Overall, the highest dimensionless figure of merit zT = 0.87 is achieved at 714 K for Nd0.9Fe3.2Co0.8Sb12. [ABSTRACT FROM AUTHOR]

This paper presents the charging and characterization of an organic micro electret array for vibration energy harvesting. Micro sized electrets with stable and high surface potential are essential for the long-term effectiveness of micro electrostatic power generators which harvest low-level vibration energy. In this study, a localized corona charging method to obtain micro sized electret areas on non-patterned macro sized dielectric thin film has been proposed to solve the problem of low charging efficiency and fast charge decay of micro sized electrets. This method involves using a shadow mask to transfer charge patterns and a triode corona charging configuration to facilitate charge penetration. Charging efficiency of 93.6% is achieved on an electret area of 100 µm × 100 µm, and 87% of its initial surface potential remains on the shrunken area of 50 µm × 50 µm after 240 days of storage. A technique combining SEM surface topography and non-contact measurement of the average surface potential has been developed to map the charge distribution on locally charged dielectric thin film and measure the surface potential on the micro sized charged area by incorporating the layout characteristic of a micro electret array. [ABSTRACT FROM AUTHOR]