Figure Of Merit ZT Research Articles

House electrical generation using thermoelectric cinder block: Case study on Lebanese hollow block

The work presented in this article describes thermoelectric effect in cinder blocks in order to generate electricity in houses through heat waste harvesting. The study consists of developing a numerical model formed by a heat transfer equation coupled to thermoelectric equations to study the performance of thermoelectric generators(TEG) incorporated inside Lebanese hollow blocks through two simulations using finite difference and finite element schemes. Results showed a voltage of 5.85 mV produced from a single 8.6 × 0.4 × 0.4 cm3 thermoelectric leg made of Bismuth Antimony Telluride for a temperature difference ΔT = 30 K. Then, a design of three TEGs with 123 thermoelectric legs incorporated inside a hollow block was tested and validated numerically using both methods, the main results obtained for ΔT = 30 K, showed a voltage ΔV = 0.72 V, a current I = 0.06 A and a figure of merit ZT = 0.55. The design was then optimized for economic purposes; an optimum model was chosen with a final cost of 8880 $. Different suggestions were also presented to enhance the thermoelectric performance of the model.

Extremely Fast and Cheap Densification of Cu2S by Induction Melting Method.

The aim of this work was to obtain dense Cu2S superionic thermoelectric materials, homogeneous in terms of phase and chemical composition, using a very fast and cheap induction-melting technique. The chemical composition was investigated via scanning electron microscopy (SEM) combined with an energy-dispersive spectroscopy (EDS) method, and the phase composition was established by X-ray diffraction (XRD). The thermoelectric figure of merit ZT was determined on the basis of thermoelectric transport properties, i.e., Seebeck coefficient, electrical and thermal conductivity in the temperature range of 300–923 K. The obtained values of the ZT parameter are comparable with those obtained using the induction hot pressing (IHP) technique and about 30–45% higher in the temperature range of 773–923 K in comparison with Cu2S samples densified with the spark plasma sintering (SPS) technique.

Ab initio prediction of enhanced thermoelectric performance from bulk to monolayer Sb2S2Te

By using the first principles investigations based on the full potential linearized augmented plane wave (FP-LAPW) method within both the generalized gradient approximation (GGA) and the Tran-Blaha modified Becke-Johnson (TB-mBJ), we predicted the electronic structure and thermoelectric properties of bulk and monolayer Sb2S2Te. Both monolayer and bulk structures of Sb2S2Te are semiconductors with an indirect band gap. The band gap can be improved with TB-mBJ. The effect of charge carriers concentration on the electrical conductivity (σ) and the electronic thermal conductivity (κeκe) for bulk Sb2S2Te has reached the level of saturation. The monolayer Sb2S2Te exhibits superior thermoelectric properties and plays a key role in the enhancement of the figure of merit for p-type doping in comparison to the bulk compound. Monolayer Sb2S2Te have ultra-low lattice thermal conductivity and larger thermoelectric (TE) figure of merit ZT. The results demonstrate that the monolayer Sb2S2Te could be potential candidate for TE applications, which has promising TE properties in p-type system.

DFT study of structural, electronic, and thermoelectric properties of Cs2PdX(X=Br2Be2Te2) compound

Materials science is based on the research of new materials with specific physical properties. In this work, we study a new family of lead-free halide perovskites Cs2PdX (X = Br2Be2Te2) which crystallizes in the triclinic structure with formation energy equal to −26.99eV, this material in high temperature presents an important advance for thermoelectric applications. For this purpose, ab-initio calculations are executed to study the structural, electronic, and thermoelectric properties of the Cs2PdX (X = Br2Be2Te2) compound. All calculations are performed using density functional theory (DFT) based on Quantum Espresso code. Generalized gradient approximations (GGA) of Perdew - Burke - Ernzerhof (PBE) have been adopted for the exchange correlation potential. The results obtained show that this material exhibits a band gap of 1.3 eV. Moreover, by using Boltzmann's theory, it was found that the figure of merit ZT is greater than 1 at a temperature of T = 1200 K. In fact, this work reveals that the Cs2PdX (X = Br2Be2Te2) compound is an ideal candidate for thermoelectric applications.

High thermopower and birefringence in layered mercury-based halides

This work presents a theoretical investigation of mercury-based halides in both bulk and monolayer form. These compounds are direct bandgap semiconductors in bulk and monolayer form as it is evident from the analysis of structural and electronic properties. Birefringence values have been used to ascribe anisotropic optical properties, which may host future opto-electronic device applications. The values of mobilities for both the carriers in HgI2 are consistent with the experimental values. The low value of lattice thermal conductivity and favorable carrier mobilities provide a better scope for thermoelectric properties. The least bandgap of HgI2 further enables thermoelectric applications, and the thermopower is found to be high with a value of 580 μV/K for holes and nearly 320 μV/K for electrons. The thermoelectric efficiency for holes is quite appreciable with a figure of merit zT around 0.5 at 300 K for a carrier concentration of 1019 cm−3. In case of monolayers, the thermopower of HgI2 monolayer is found to be higher than its bulk counterpart. Our findings show that these compounds have robust transport and optical properties, which await future experimental verifications.

Effect of electric fields on the electronic and thermoelectric properties of zigzag buckling silicene nanoribbons

We investigate the electronic structure and the thermoelectric transport properties of zigzag buckling silicene nanoribbons (BSiNRs) under the effect of external electric fields by means of atomistic simulations. The obtained results show that thanks to the buckling feature, zigzag BSiNRs have a stronger response to a vertical electric field compared to its flat form structure and also single-layer and bi-layer graphene nanoribbons with zigzag edges (GNRs & BGNRs). An inverse is observed in the case of a transverse electric field. Interestingly, the mutual effect when applying simultaneously the vertical and transverse fields induces a larger bandgap compared to individual ones. The mutual effect observed with zigzag BSiNRs is much more pronounced compared to that in zigzag BGNRs since the vertical field has a modest effect on zigzag BGNRs stemming from weak van der Waals interactions between graphene layers. Thermoelectric performance of zigzag BSiNRs is enhanced remarkably with electric fields in which the figure of merit ZT can be tuned to exceed 1. Interestingly, although the mutual impact of two external fields induces the largest Seebeck coefficient, it unveils that the vertical electric field is overall more efficient in enhancing the thermoelectric performance of zigzag BSiNRs. In addition, the enhancement of ZT is demonstrated to stem mainly from a dramatical degradation of the electron thermal conductance around the Fermi level. This study shows that zigzag BSiNRs in combination with external electric fields have favourable advantages for different electronic and thermoelectric applications.

The efficiency of short sintering time on thermoelectric properties of delafossite CuCr0:85Mg0:15O2 ceramics

Introduction: Harvesting the waste heat emitted from the activities of humanity based on thermoelectric devices is an appropriate way to reduce the overconsumption of fossil fuel nowadays.
 Methods: In this work, CuCr0:85Mg0:15O2 compounds prepared by conventional solid-state reaction method were investigated to find out that the short sintering time is enough for thermoelectric applications, directly low the cost of the devices.
 Results and Conclusion: We find out that there is a significant change in the crystal structure, the chemical state, and thermoelectric properties along with the increase of the sintering time, but eventually, the dimensionless figure of merit ZT is almost constant regardless of the long or short sintering time which means that the increase of electrical conductivity will compromise the increase of thermal conductivity. The highest ZT value is 0.03 measured at 500 oC for both samples prepared at the sintering time of 3 and 12 hours.

Improvement electronic and magnetic properties of Cr impurity doped PbSe for optoelectronic devices applications: a first-principles proposal

To produce innovative spintronics components, we are now looking for ferromagnetic semiconductors at room temperature. The aim of this work is to study the electronic structures and the magnetic properties is to trigger ferromagnetism and to improve the band gap of PbSe The study of the electronic structure and the magnetic properties of diluted magnetic semiconductors (DMS) type IV–VI PbSe doped Cr is investigated in detail. Our results are as follows. We then calculated the sp-d exchange couplings between electrons (holes) of the conduction (valence) band and magnetic impurities. The topology of the band structure shows that our material is half metal, which has a direct gap in the minority channel due to the nature of sp–d coupling. The values of N $$\alpha $$ ferromagnetic and N $$\beta $$ antiferromagnetic obtained in the mean-field approximation are of the order of 0.551 and $$-0.445$$ eV respectively. The Thermoelectric Conversion Efficiency focuses on a single dimension parameter, the figure of merit ZT. We have seen that doping with Cr can also have a beneficial effect on thermal conductivity and consequently on ZT. This leads our material among the best compounds to thermoelectric applications.

Improved Electrical, Thermal, and Thermoelectric Properties Through Sample‐to‐Sample Fluctuations in Near‐Percolation Threshold Composite Materials

AbstractEffective medium theories (EMT) are powerful tools to calculate sample averaged thermoelectric material properties of composite materials. However, averaging over the heterogeneous spatial distribution of the phases can lead to incorrect estimates of the thermoelectric transport properties and the figure of merit ZT in compositions close to the percolation threshold. This is particularly true when the phases’ electronic properties are rather distinct leading to pronounced percolation effects. The authors propose an alternative model to calculate the thermoelectric properties of multi‐phased materials that are based on an expanded nodal analysis of random resistor networks (RRN). This method conserves the information about the morphology of the individual phases, allowing the study of the current paths through the phases and the influence of heterogeneous charge transport and cluster formation on the effective material properties of the composite. The authors show that in composites with strongly differing phases close to the percolation threshold the thermoelectric properties and the ZT value are always dominated exclusively by one phase or the other and never by an average of both. For these compositions, the individual samples display properties vastly different from EMT predictions and can be exploited for an increased thermoelectric performance.

Thermoelectric Characteristics of A Single-Crystalline Topological Insulator Bi2Se3 Nanowire.

The discovery of topological insulators (TIs) has motivated detailed studies on their physical properties, especially on their novel surface states via strong spin–orbit interactions. However, surface-state-related thermoelectric properties are rarely reported, likely because of the involvement of their bulk-dominating contribution. In this work, we report thermoelectric studies on a TI bismuth selenide (Bi2Se3) nanowire (NW) that exhibit a larger surface/volume ratio. Uniform single-crystalline TI Bi2Se3 NWs were successfully synthesized using a stress-induced growth method. To achieve the study of the thermoelectric properties of a nanowire (NW), including electrical conductivity (σ), Seebeck coefficient (S), and thermal conductivity (κ), a special platform for simultaneously performing all measurements on a single wire was designed. The properties of σ, S, and κ of a 200 nm NW that was well precharacterized using transmission electron microscope (TEM) measurements were determined using the four-probe method, the two-probe EMF across ∇T measurement, and the 3ω technique, respectively. The integrated TE properties represented by the figure of merit ZT (S2σT/κ) were found to be in good agreement with a theoretical study of Bi2Se3 NW.

Two-dimensional square-Au2S monolayer: A promising thermoelectric material with ultralow lattice thermal conductivity and high power factor* *Project supported by the Doctoral Research Fund of Southwest University of Science and Technology (Grant No. 21zx7113) and the National Natural Science Foundation of China (Grant Nos. 11804284 and 11802280).

The search for new two-dimensional (2D) harvesting materials that directly convert (waste) heat into electricity has received increasing attention. In this work, thermoelectric (TE) properties of monolayer square-Au2S are accurately predicted using a parameter-free ab initio Boltzmann transport formalism with fully considering the spin–orbit coupling (SOC), electron–phonon interactions (EPIs), and phonon–phonon scattering. It is found that the square-Au2S monolayer is a promising room-temperature TE material with an n-type (p-type) figure of merit ZT = 2.2 (1.5) and an unexpected high n-type ZT = 3.8 can be obtained at 600 K. The excellent TE performance of monolayer square-Au2S can be attributed to the ultralow lattice thermal conductivity originating from the strong anharmonic phonon scattering and high power factor due to the highly dispersive band edges around the Fermi level. Additionally, our analyses demonstrate that the explicit treatments of EPIs and SOC are highly important in predicting the TE properties of monolayer square-Au2S. The present findings will stimulate further the experimental fabrication of monolayer square-Au2S-based TE materials and offer an in-depth insight into the effect of SOC and EPIs on TE transport properties.

Thermoelectric properties of α -In2Se3 monolayer

Thermoelectric (TE) properties of monolayered α-In2Se3 are investigated using the first-principles calculations based on the density functional theory and Boltzmann transport theory. The results show that monolayered α-In2Se3 is a great candidate for high-performance thermoelectric materials with the power factor PF and the figure of merit ZT as high as 0.02 W/mK2 and 2.18 at room temperature, respectively. We attribute such great TE performance to the large electrical conductivity and low lattice thermal conductivity, which originate from unique band structures of group III chalcogenides and anharmonic scattering. Furthermore, we prove that the quantum confinement effect can realize up to an order of magnitude enhancement in the PF. Our findings may open up new possibilities for two-dimensional thermoelectric materials in practical applications.

Thermal Conductivity and Thermoelectric Power of Compounds in the Cu–Ge–As–Se System

The influence of temperature (in the interval of 300–400 K) and concentrations on the electrical conductivity, thermal conductivity, and thermoelectric power of copper chalcogenide-based crystals with the general formula (GeSe)1 – x(CuAsSe2)x has been considered. Heat transfer mechanisms have been determined. It has been found that the temperature dependence of thermal conductivity is nonmonotonic with a singularity at 358 K. Thermoelectric figure of merit ZT has been calculated.

N-type organic thermoelectrics: demonstration of ZT\u2009>\u20090.3

The ‘phonon-glass electron-crystal’ concept has triggered most of the progress that has been achieved in inorganic thermoelectrics in the past two decades. Organic thermoelectric materials, unlike their inorganic counterparts, exhibit molecular diversity, flexible mechanical properties and easy fabrication, and are mostly ‘phonon glasses’. However, the thermoelectric performances of these organic materials are largely limited by low molecular order and they are therefore far from being ‘electron crystals’. Here, we report a molecularly n-doped fullerene derivative with meticulous design of the side chain that approaches an organic ‘PGEC’ thermoelectric material. This thermoelectric material exhibits an excellent electrical conductivity of >10 S cm−1 and an ultralow thermal conductivity of <0.1 Wm−1K−1, leading to the best figure of merit ZT = 0.34 (at 120 °C) among all reported single-host n-type organic thermoelectric materials. The key factor to achieving the record performance is to use ‘arm-shaped’ double-triethylene-glycol-type side chains, which not only offer excellent doping efficiency (~60%) but also induce a disorder-to-order transition upon thermal annealing. This study illustrates the vast potential of organic semiconductors as thermoelectric materials.

Low thermal conductivity and enhanced Seebeck coefficient in Antimony and Selenium co-doped PbTe Nanopowders

We report a new method to synthesize Sb and Se co-doped PbTe nanopowders by a simple aqueous chemical method without the assistance of any surfactant or template. X-ray diffraction studies revealed that the prepared nanopowders are polycrystalline in nature and crystallize in the face-centered-cubic (fcc) PbTe structure. SEM and TEM studies reveal that Sb and Se co-doped PbTe nanopowders consist of an interconnected network of spherical nanoparticles with diameters around 12 nm. Seebeck coefficient of the undoped PbTe (436 µV/K at 301 K) and co-doped PbTe (627 µV/K at 301 K) is enhanced compared to that of the bulk PbTe (265 µV/K at 298 K) and the thermal conductivity is drastically decreased [undoped PbTe (0.265 W/m-K) and co-doped PbTe (0.525 W/m-K) at 378 K] compared with the value for the bulk PbTe (2.2 W/m-K at 300 K). The dimensionless figure of merit ZT attains its maximum value 0.055 at 378 K for undoped and 1.09 × 10−5 at 352 K for co-doped PbTe.

Integrated SnSSe bulk and monolayer as industrial waste heat thermoelectric materials

New, nontoxic and earth‐abundant materials for heat‐energy interconversion are urgently required to mitigate the over‐reliance on finite fossil fuels supply. Herein, using ab initio quantum mechanical calculations and Boltzmann theory, optimization of thermoelectric performances instable, mechanically robustCm‐SnSSe and P3m1‐SnSeS phases was performed. These phases exhibit an intrinsically low thermal conductivity of ~1.00 W m−1 K−1 at room temperature. Beyond 400 K, both phases display satisfactory thermoelectric performances, namely figure of merit ZT > 0.7 and power factor PF > 3.0 mW K−2 m−1. Better performances were obtained through holes doping at 1020 cm−3 concentration, where their ZT values reach 0.9 at 500 K and fluctuate minimally over broad temperature plateau, retaining the high PF over 3.0 mWK−2 m−1. Evolution into layered structure is also possible, with the calculated p‐type doping of P3m1‐SnSSe monolayer displaying decent ZT ~ 0.7 and very high PF > 6.0 mWK−2 m−1 beyond 300 K. In bulk form, the study specimens display superior machinability and mechanical properties, as evidenced by the approximately 8‐fold increase in their Vickers hardness when compared to PbTe and Bi2Te3 materials, while maintaining their plasticity characteristic. The computed E2D of 55.50 N m−1 is relatively low, which means Sn‐S‐Se alloy remains ductile when progressing to 2D state. Biaxial strain‐induced results show enhanced anharmonicity phonon scattering and thermopower increment, enabling maximum ZT ~ 1.0 and PF > 7.0 mW m−1 K−2 to be achieved in the appealing industrial waste heat akin 373 ≤ T ≤ 773 K range under 10% tensile strain.

A Study on N-Type Bismuth Sulphochloride (BiSCl): Efficient Synthesis and Characterization

Irregular rod-like bismuth sulphochloride (BiSCl) was synthesized by a high efficiency process in which BiCl3 and Bi2S3 were fully ground and mixed in N2 atmosphere followed by a sintering at 227∘C for 9 h to achieve crimson BiSCl powder. The products were characterized by X-ray powder diffraction (XRD) and scanning electronic microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX). The BiSCl is an n-type semiconductor with a bandgap of 1.9 eV. In the temperature range of 300–500 K, thermal conductivity, electrical conductivity, Seebeck coefficient and thermoelectric figure of merit ZT of the BiSCl were tested and calculated. It is resulted that the BiSCl has a thermal conductivity of 0.45 Wm−1K−1 at 500 K and a Seebeck coefficient of −579 μVK−1 at 400 K. This work will help inform future in-depth studies on possible applications of BiSCl in the fields of thermoelectricity, optoelectronics and photocatalyticity.

High accuracy testbed for thermoelectric module characterization

In this paper, we present an improved version of the unified method (UM) for thermo-electric modules (TEM) characterization with the aim to reduce the overall parameters uncertainty. The parameters that make up the commonly accepted figure of merit Z or zT¯ are mainly affected by temperature related uncertainty, which also significantly limit the precision of the test conditions and thus the reliability of derived models. To overcome these limitations, we conceived a novel and simplified measurement setup that relies at the same time on thermistor technology rather than thermocouple and on a lower number of required components. The improved setup, exploits a solid calibration procedure to reduce the uncertainty in temperature measurements from 1.4 °C typical of a J-type thermocouple (Class 1 IEC-EN 60584-2) to 0.027 °C with calibrated thermistors, leading to a previously unachievable millidegree-precision temperature control and to an uncertainty drop of two orders of magnitude in all the temperature-derived measurements. Such improvement has a direct feedback on both the αS and Θ, leading to a drop of a least one order of magnitude for a ΔT of 3 °C and more than 44 times for the latter at 30 °C. As result, the figure of merit zT¯can now be determined with an uncertainty equal to 0.58%.

Creep behavior and post-creep thermoelectric performance of the n-type Skutterudite alloy Yb0.3Co4Sb12

Upon uniaxial compressive loading at 500 °C (T/Tm = 0.67, where Tm is the absolute melting point), the n-type Skutterudite alloy Yb0.3Co4Sb12 deforms plastically by creep via a power-law, with a stress exponent ∼3 consistent with dislocation viscous glide. An activation energy of 171 kJ/mol is measured over the temperature range of 500–587 °C (T/Tm = 0.67–0.75) at a stress of 30 MPa. Yb0.3Co4Sb12 is ductile at 500 °C, exhibiting a compressive strain of 25% when subjected to stresses ranging from 22 to 90 MPa for up to 28 days. Among the thermoelectric materials tested so far for creep, Yb0.3Co4Sb12 exhibits a creep resistance intermediate between low-melting (Bi2Te3, TAGS-85) and high-melting thermoelectrics (Mg2Si and ZrNiSn). A relatively modest drop in the figure of merit zT, from 0.67 to 0.52, is displayed by Yb0.3Co4Sb12 after accumulating 3.7% compressive creep strain at 500 °C, mostly due to a drop in electrical conductivity.

Remarkable intrinsic ZT in the 2D PtX2(X = O, S, Se, Te) monolayers at room temperature

Two-dimensional (2D) thermoelectric (TE) materials which have the figure of merit ZT that is greater than 1.0 at room temperature would be highly desirable in energy conversion. Here, we study the thermoelectric properties of the 2D PtX2 (X = O, S, Se, Te) monolayers by using first-principles calculations within the ballistic transport region. The 2D PtX2 monolayers have nearly degenerated valleys in conduction bands, and also a very flat curvature around the extrema in both the conduction and valance bands near the Fermi level, which enhance the power factor. Moreover, as compared to many other 2D semiconductors, the 2D PtX2 monolayers possess a lower lattice thermal conductivity, which ranges from 0.207 WK−1m−1 to 0.643 WK−1m−1. These excellent electronic and thermal properties lead to the impressive ZT of 1.65 (PtTe2), 1.42 (PtS2), 0.94 (PtO2) and 0.84 (PtSe2) at 300 K, respectively. Moreover, large ZT of 1.29 (PtS2) and 1.02 (PtTe2) can still be achieved upon applying a 1% tensile strain on the lattice. These results indicate that the 2D PtX2 monolayers are promising TE materials for room temperature applications.