Good Thermoelectric Performance Research Articles

Ultralow lattice thermal conductivity and anisotropic thermoelectric performance of AA stacked SnSe bilayer

The low-temperature bulk phase of SnSe has a layered structure with AB-type of stacking of two-atom-thick SnSe monolayers. However, in the case of bilayers the AA-stacked SnSe bilayer structure is most stable. Similar to bulk SnSe, AA-stacked SnSe bilayer has ultralow lattice thermal conductivity of 0.90 Wm−1 K−1 at room temperature which is quite low as compared to other two dimensional materials. Our results show that n-type SnSe bilayer has good thermoelectric performance as compared to that of the p-type bilayer.

Good stability and high thermoelectric performance of Fe doped Cu1.80S.

Copper sulfides have attracted great attention recently in the thermoelectric community due to the liquid-like behavior of Cu ions. Among the numerous copper sulfides, digenite Cu1.80S has a poorer thermoelectric performance but better stability than the state-of-the-art binary copper sulfide Cu1.97S. In this study, good stability and high thermoelectric performance were simultaneously obtained in Fe-doped Cu1.80S. Because Fe ions will not form a concentration gradient under an external field to change the critical voltage, Fe-doped Cu1.80S samples inherit the good stability of the pristine Cu1.80S. The critical voltage for Cu1.80Fe0.064S is 0.16 V at 750 K, which has been the largest value reported so far. Likewise, the Fe dopants can significantly improve the thermoelectric performance by suppressing the too high electrical conductivity of Cu1.80S. The peak dimensionless figure of merit (zT) for Cu1.80Fe0.064S is around 0.8 at 750 K, about four times that of Cu1.80S. The average zT for Cu1.80Fe0.064S is 0.40 in 300-750 K, which is amongst the highest values in reported thermoelectric sulfides. Combining the good stability and high thermoelectric performance, the present Cu1.80Fe0.064S has great potential to be used in the application of waste heat harvesting in the middle temperature range.

Self‐Healable and Stretchable Organic Thermoelectric Materials: Electrically Percolated Polymer Nanowires Embedded in Thermoplastic Elastomer Matrix

AbstractSelf‐healable and stretchable energy‐harvesting materials can provide a new avenue for the realization of self‐powered wearable electronics, including electronic skins, whose main materials are required to be robust to and stable under external damage and severe mechanical stresses. However, thermoelectric (TE) materials showing both self‐healing properties and stretchability have not yet been demonstrated despite their great potential to harvest thermal energy in the human body. As most existing TE materials are either mechanically brittle or unrecoverable after being subjected to damage, a novel approach is necessary for designing such materials. Herein, self‐healable and stretchable TE materials based on all‐organic composite system wherein polymer semiconductor nanowires are p‐doped with a molecular dopant and embedded in a thermoplastic elastomer matrix are reported. The polymer nanowires are electrically percolated in the matrix, and the resulting composite materials exhibit good TE performance. The composites also exhibit both excellent self‐healing properties under mild heat and pressure conditions and good stretchability. It is believed that this work can be a cornerstone for the design of self‐healable and stretchable energy‐harvesting materials as it provides useful guidelines for imparting electrical conductivity to insulating thermoplastic elastomers, which typically possess versatile and useful mechanical properties.

High-temperature power factor of half-Heusler phases RENiSb (RE = Sc, Dy, Ho, Er, Tm, Lu)

Study on half-Heusler compounds RENiSb, RE = Sc, Dy, Ho, Er, Tm, Lu, was performed in perspective of high-temperature thermoelectric application. Relatively small electrical resistivity (4–60 μΩm in 300–1000 K) combined with fairly high positive Seebeck coefficient (40–160 μV/K) yielded for the RENiSb ternaries rather large thermoelectric power factors at 750 K, namely 14 μW K−2cm−1 for ScNiSb and 11 μW K−2cm−1 for TmNiSb. At room temperature the thermal conductivity measured for the two materials was 8.1 W K−1m−1 and 4.4 W K−1m−1, respectively. The value obtained for the latter compound is smaller than those reported for unoptimized half-Heusler phases based on d-electron elements. This finding may be explained by strong point defect scattering occurring due to intrinsic disorder in crystal structure of TmNiSb, or to smaller extent by enhanced scattering on incoherent grain boundaries with the impurity phases. Nevertheless, achieving good thermoelectric performance of the RENiSb phases at high temperatures requires proper tuning of carrier concentration, as well as further reduction in their thermal conductance by means of alloying and/or nanostructurization.

Optical and thermoelectric response of RhTiSb half-Heusler

Structural, electronic, optical and thermoelectric response of the cubic RhTiSb compound is reported using TB-mBJ potential. The calculated results for the band structure and DOS confirm that the RhTiSb is a nonmagnetic (NM) semiconductor with an indirect bandgap of 0.71 eV. The main optical parameters such as dielectric function, absorption coefficient, refractive index and optical reflectivity were estimated for emission upto 14 eV. The RhTiSb half-Heusler exhibits a maximum absorption in the visible and ultraviolet region. By using the Boltzmann transport equations as incorporated in BoltzTraP code, the thermoelectric characteristics were calculated. The main properties which describe the aptitude of material in thermoelectric environment such as Seebeck coefficient and figure of merit were calculated. The high values of figure-of-merit (ZT [Formula: see text] 0.7) were observed in large range of temperature indicating that RhTiSb have a good thermoelectric performance.

First principles investigation on elastic, optoelectronic and thermoelectric properties of KYX (X = Ge, Sn and Pb) half-heusler compounds

Theoretical calculations based on the density functional theory and the Boltzmann semi-classical transport theory have been carried out to examine the structural, elastic, electronic, optical and thermoelectric properties of Potassium- and Yttrium-based half-Heusler (HH) compounds KYX (X = Ge, Sn and Pb). Based on our calculations, KYGe, KYSn, and KYPb HH compounds are mechanically stable, and show semiconductor nature with direct band gaps of 0.852, 0.921, and 0.927 eV, respectively, which are obtained from mBJ level of theory. Moreover, the KYSn is brittle, while the KYGe and KYPb are dutile. The optical results show that these HH compounds have wide absorption band from high energy region of infrarred to ultraviolet region. At high photon energies (beyond of 13 eV), they shows very small reflectivity. Because of their favorable electronic structure, these materials have very good thermoelectric performance with high thermopower and figure of merit. The effect of temperature on thermoelectric properties also is discussed in details.

Ternary sulfides BaLa2S4 and CaLa2S4 as promising photocatalytic water splitting and thermoelectric materials: First-principles DFT calculations

Both ternary sulfides, BaLa2S4 and CaLa2S4, are found to possess a suitable band gap for absorbing visual light; moreover, the ECB and EVB are at right positions allowing the photo-generated electron/hole pairs to split water. The valence band of BaLa2S4 (CaLa2S4) are characterized by high peaks at −1 eV and −2 eV, and strong hybridization of S/La-p and Ba-s (Ca-s/p) states. These features help to enhance the separation of electron/hole pairs. Meanwhile, the conduction band has high peak at 3 eV, which is mostly constructed by hybridization of La-f, La-d and Ba-s (Ca-s/p) states. The conduction band's smooth dispersion is favorable for inter-band transition, thus it enhances the absorption rate of two considered compounds. The Ba/Ca/La–S bonds are predominantly covalent with electronegativity difference of about 31–38%. The large difference in effective mass between electron and hole enhances the separation of electron/hole pairs. CaLa2S4 and BaLa2S4 are p-type semiconductors with positive thermopower S of about 229.8 μV/K and 234.8 μV/K, respectively, at Fermi level (μ = 0) and temperature 300 K. Both materials show good thermoelectric performance for hole concentration being in the range 1 × 1019–1x1021 cm-3. The electronic figure of merit ZTe marks the highest value of about 0.95 and 0.97 at 2 × 1019 cm-3 for CaLa2S4 and BaLa2S4, respectively.

$${\hbox {LDA}}+{\hbox {U}}$$ LDA + U Calculation of Electronic and Thermoelectric Properties of Doped Tetrahedrite $${\hbox {Cu}}_{12}{\hbox {Sb}}_{4}{\hbox {S}}_{13}$$ Cu 12 Sb 4 S 13

Tetrahedrite-based thermoelectric materials have received much attention in recent years due to their good thermoelectric performance and earth-abundance. The parent compound $${\hbox {Cu}}_{12}{\hbox {Sb}}_{4}{\hbox {S}}_{13}$$ exhibits a high power factor and low lattice thermal conductivity. Further enhancement of the thermoelectric figure of merit ZT is expected in substituted compounds, primarily at the Cu site $${\hbox {Cu}}_{12-x}{\hbox {M}}_{x}{\hbox {Sb}}_{4}{\hbox {S}}_{13}$$ . In this work we have studied the impact of substitution effects on thermoelectric properties using density-functional theory electronic structure calculations in combination with calculation of electrical transport properties by the BoltzTrap program.

Thermal stability of p-type Ag-doped Mg3Sb2 thermoelectric materials investigated by powder X-ray diffraction.

The thermal stability of the p-type Mg2.985Ag0.015Sb2 material with reported good thermoelectric performance is systematically investigated using powder X-ray diffraction (PXRD). Rietveld refinements were performed to extract the quantitative compositional and structural information from PXRD data. For both densified bulk samples and powdered samples of Mg2.985Ag0.015Sb2 studied under vacuum, a secondary phase, Sb, appears upon the first heating process at temperatures above 500 K, but the amount of the Sb phase stabilizes in subsequent thermal cycles. This is consistent with the good repeatability of the electrical resistivity data after the first cycle measurement, and it indicates that the appearance of the Sb phase does not result in structural decomposition or degradation of the thermoelectric properties. To investigate the effect of the Mg vacancy concentration on the formation of the secondary Sb phase, Mg3.5-xAgxSb2 (x = 0 and 0.015) samples with nominal excess Mg were synthesized and characterized. Compared with Mg2.985Ag0.015Sb2, it is found that Mg3.5-xAgxSb2 (x = 0.015) shows no Sb phase appearing for the bulk sample after heat treatment, and only a small amount of Sb emerges in the powdered sample. This reveals that decreasing the Mg deficiency is beneficial for reducing the amount of emerging Sb secondary phase. In addition, there is less Sb appearing in the Ag-doped powder sample of Mg3.5-xAgxSb2 (x = 0.015) than the undoped Mg3.5Sb2 powder sample, indicating that Ag doping at the Mg sites can inhibit the appearance of the Sb phase to some extent. Our work implies that the emergence of the Sb phase is unlikely due to the decomposition of the Mg3Sb2 structure and can be hindered by reducing the Mg deficiency or Ag doping on the Mg sites.

A simple chemical guide for finding novel n-type dopable Zintl pnictide thermoelectric materials

Computations have predicted good thermoelectric performance of n-type doped Zintl phases. We present a simple, yet effective, chemical guide for finding n-type dopable Zintl pnictides and perform a large-scale search to identify candidate materials.

Electronic structure and thermoelectric properties of Ta-based half-Heusler compounds with 18 valence electrons

Recently, the half-Heusler compounds with 18 valence electrons have been considered as promising candidate for thermoelectric applications due to their interesting properties. In this work, the structural, electronic and thermoelectric properties of Ta-based half-Heusler TaXY (X = Ru, Rh; X = Sb, Bi, Sn and Pb) have been investigated using the full-potential linearized augmented plane-wave (FP-LAPW) method within the density functional theory (DFT) and the classical Boltzmann transport theory. Generalized gradient approximation as parameterized by Wu-Cohen (GGA-WC) and Tran-Blaha modified Becke-Johnson exchange potential (mBJ) are employed for taking on account the exchange-correlation electron potential. All four studied materials are semiconductor with indirect band gap 0.815 eV for TaRuSb, 0.906 eV for TaRuBi, 1.109 eV for TaRhSn and 1.138 eV for TaRhPb. Additionally, the spin-orbit coupling (SOC) decreases slightly the band gap of these materials. Thermoelectric properties, such as, Seebeck coefficient, electrical conductivity, power factor, total thermal conductivity and figure of merit are calculated in function of chemical potential. Obtained results show that TaXY compounds have good thermoelectric performance with high figure of merit value 0.99.

Enhancement of Conductivity and Thermoelectric Property of PEDOT:PSS via Acid Doping and Single Post‐Treatment for Flexible Power Generator

AbstractPoly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising thermoelectric (TE) material. Nonetheless, its practical application is hindered by the poor TE properties of the pristine PEDOT:PSS and complicated treatment procedures. Enhancing its electrical conductivity is a key step for the improvement of TE properties. Here, a simple method is introduced to enhance the conductivity by adding sulfonic acid into the PEDOT:PSS solution. A systematic study of representative sulfonic acids with various functional groups suggests that steric effect induced by the functional groups has remarkable impact on the conductivity. The highest conductivity of 1996 S cm−1 is observed in benzenesulfonic acid‐doped PEDOT:PSS films. The doped PEDOT:PSS films are further treated with dimethyl sulfoxide and hydrazine successively or synchronously to tune the oxidation level. A maximum power factor (PF) of 203.1 µW m−1 K−2 is obtained. The high PF of treated PEDOT:PSS allows the realization of a flexible thermoelectric generator, which can generate 4.6 mV thermovoltage when attached on human skin. It also shows a good linear response with the increase of temperature difference; thus, it can be potentially used as a flexible thermal sensor. The facile fabrication process and good TE performance provide PEDOT:PSS an opportunity in wearable electronics.

Thermoelectric properties in monolayer $$\hbox {MoS}_2$$ MoS 2 nanoribbons with Rashba spin–orbit interaction

In this work, we present a detailed investigation of the influences of intrinsic spin–orbit coupling (ISOC) as well as Rashba spin–orbit coupling (RSOC) on thermoelectric properties of molybdenum disulfide ( $$\hbox {MoS}_2$$ ) nanoribbons with armchair and zigzag edges, theoretically. For this purpose, we generalize the tight-binding model including the effects of the ISOC on all the atoms and a RSOC induced by a vertical electric field. By the calculation of the quantum spin-dependent transmission function from the recursive non-equilibrium Green’s function model using the multi-band Slater–Koster tight-binding method, the electrical and thermal currents flowing to the right lead can be obtained from the Landauer–Buttiker formulae. Hence, the temperature-dependent electrical conductance (G), the thermal conductivity ( $$\kappa $$ ), the Seebeck thermopower (S), and the thermoelectric efficiency (ZT) are discussed. The results predict a noticeable semiconducting behavior with n type, which exhibits a linear temperature dependence of the gap energy for both nanoribbons. The predicted ZT values demonstrate that the $$\hbox {MoS}_2$$ nanoribbons can be optimized to exhibit very good thermoelectric performance in which its value is not affected under influence of the electric field-induced RSOC in the ZMoS $$_2$$ nanoribbon (regardless of the AMoS $$_2$$ nanoribbon). Based on the used model, a large Seebeck coefficient is obtained in both types of the nanoribbons. Our results may be useful in designing novel thermoelectric devices based on two-dimensional materials as one of suitable nanoscale device.

Use of H2-Ar gas mixtures in radio-frequency magnetron sputtering to produce high-performance nanocrystalline bismuth telluride thin films

Nanocrystalline bismuth telluride (Bi2Te3) thin films with good thermoelectric performance were prepared using mixtures of hydrogen and argon gas by radio-frequency magnetron sputtering. The effects of hydrogen addition on the surface morphology, crystal structure, elemental composition, and thermoelectric properties of the Bi2Te3 thin films were investigated. The mixing ratio, H2/(H2 + Ar), was varied from 0 to 15%. The thin films were deposited on glass substrates heated at 200 °C. It was observed that the surface morphologies of the thin films were greatly affected by the mixing ratio. The deposition rate and composition ratio Te/(Bi+Te) decreased with increasing mixing ratio, indicating that tellurium atoms evaporated from the film surface by a chemical reaction between hydrogen and tellurium. The oxygen concentration inside the films decreased as the mixing ratio increased, resulting in an increased power factor. A maximum power factor of 9.0 μW/(cm·K2) was observed at a mixing ratio of 10%, as this thin film showed a relatively high electrical conductivity and high Seebeck coefficient. However, at a higher mixing ratio of 15%, the power factor of the thin film drastically decreased, possibly due to the appearance of the hexagonal BiTe phase, which exhibits metallic characteristics. Therefore, we conclude that the addition of a moderate amount of hydrogen (10%) during sputtering can improve the thermoelectric performance of Bi2Te3 thin films.

Synthesis and thermoelectric properties of Rashba semiconductor BiTeBr with intensive texture

Bismuth tellurohalides with Rashba-type spin splitting exhibit unique Fermi surface topology and are developed as promising thermoelectric materials. However, BiTeBr, which belongs to this class of materials, is rarely investigated in terms of the thermoelectric transport properties. In the study, polycrystalline bulk BiTeBr with intensive texture was synthesized via spark plasma sintering (SPS). Additionally, its thermoelectric properties above room temperature were investigated along both the in-plane and out-plane directions, and they exhibit strong anisotropy. Low sound velocity along two directions is found and contributes to its low lattice thermal conductivity. Polycrystalline BiTeBr exhibits relatively good thermoelectric performance along the in-plane direction, with a maximum dimensionless figure of merit (ZT) of 0.35 at 560 K. Further enhancements of ZT are expected by utilizing systematic optimization strategies.

Revealing optoelectronic and transport properties of potential perovskites Cs2PdX6 (X = Cl, Br): A probe from density functional theory (DFT)

Metal-halide perovskites are rapidly emerging crystalline materials that are reasonably preferred as leading aspirant for applications in optoelectronic and thermoelectric devices. In this paper, we have thoroughly reviewed and performed calculations to reveal optoelectronic and transport properties for a potential newcomer, Cs2PdX6 (X = Cl, Br) termed as Cesium Palladium Halides (CPH). Outcome of present computations are compared with available results and a reasonable agreement is recorded. Energy band gap computations performed reveal indirect band gap of 2.29 eV for Cs2PdCl6, which substantially reduces to 1.22 eV when ‘Cl’ is replaced by ‘Br’. Optical absorption spectra investigations performed here, in the energy range from 3 to 5 eV confirms effective utilization of these compounds in solar cells and other optoelectronic applications. In addition, the transport properties computations performed using semi-classical Boltzmann theory, shows constant pattern of thermo power near ambient temperature range (200–500 K), which admits possible utilization of these compounds as low temperature thermoelectric materials. Performed ZT calculations demonstrates reasonably good thermoelectric performance for both materials, as there exist minor variation (0.1) in the values over wide temperature ranges i.e. from 100 to 800 K. Further, detailed analysis of transport properties predicts p-type semiconducting nature of the present series of materials.

Thermoelectric properties of polycrystalline palladium sulfide.

Measurement of the electrical, thermal, and structural properties of palladium sulfide (PdS) has been conducted in order to investigate its thermoelectric performance. A tetragonal structure with the space group P42/m for PdS was determined from X-ray diffraction measurement. The obtained power factor of 27 μW cm−1 K−2 at 800 K is the largest value obtained for the transition metal sulfides studied so far. The maximum value of the dimensionless figure of merit is 0.33 at 800 K. These results indicate that binary bulk PdS has promising potential for good thermoelectric performance.

Impact of Nb vacancies and p-type doping of the NbCoSn-NbCoSb half-Heusler thermoelectrics.

The half-Heuslers NbCoSn and NbCoSb have promising thermoelectric properties. Here, an investigation of the NbCo1+ySn1-zSbz (y = 0, 0.05; 0 ≤ z ≤ 1) solid-solution is presented. In addition, the p-type doping of NbCoSn using Ti and Zr substitution is investigated. Rietveld analysis reveals the gradual creation of Nb vacancies to compensate for the n-type doping caused by the substitution of Sb in NbCoSn. This leads to a similar valence electron count (∼18.25) for the NbCo1+ySn1-zSbz samples (z > 0). Mass fluctuation disorder due to the Nb vacancies strongly decreases the lattice thermal conductivity from 10 W m-1 K-1 (z = 0) to 4.5 W m-1 K-1 (z = 0.5, 1). This is accompanied by a transition to degenerate semiconducting behaviour leading to large power factors, S2/ρ = 2.5-3 mW m-1 K-2 and figures of merit, ZT = 0.25-0.33 at 773 K. Ti and Zr can be used to achieve positive Seebeck values, e.g. S = +150 μV K-1 for 20% Zr at 773 K. However, the electrical resistivity, ρ323K = 27-35 mΩ cm, remains too large for these materials to be considered useful p-type materials.

Understanding the combustion process for the synthesis of mechanically robust SnSe thermoelectrics

Recently, very good thermoelectric performance in both n-type and p-type SnSe has been achieved but was accompanied by poor mechanical properties. Moreover, the synthesis routes used, either the Bridgeman method for single crystal growth or conventional melting methods for polycrystalline samples, are highly energy and time intensive. In the present study, single phase SnSe was synthesized by the Self-Propagating High Temperature Synthesis (SHS) combined with Spark Plasma Sintering (SPS) in a very short time of less than 1h, and with minimum consumed energy. The thermodynamic and kinetic parameters, as well as the role of a pre-synthesized powder of SnSe added to the elemental Se and Sn powders prior to the SHS process, were systematically investigated for the first time. The presence of the pre-synthesized SnSe powder in the mixture of elemental Se and Sn powders promotes multipoint nucleation and inhibits the grain growth, resulting in a weak preferential orientation after SHS that is maintained in the bulk samples after SPS. Thermoelectric and mechanical properties of such samples are superior in comparison to the samples that do not contain the pre-synthesized powder of SnSe in the starting material. The compressive strength, bending strength and fracture toughness of the sample containing 30% of the pre-synthesized SnSe were 74.7MPa, 40.6MPa and 0.32MPam1/2, respectively. A maximum ZT value of 0.5 was achieved for this sample at 773K, which is comparable with polycrystalline samples synthesized by the conventional melting method. This work shows that the SHS reaction combined with SPS densification is an exceptionally rapid and cost effective synthesis process that yields mechanically robust bulk SnSe, a crucial step for large scale commercial applications of this thermoelectric material.

Structural, electronic, optical and thermoelectric investigations of antiperovskites A3SnO (A = Ca, Sr, Ba) using density functional theory

Density functional theory study of the structural, electrical, optical and thermoelectric behaviors of very less investigated anti-perovskites A3SnO (A = Ca, Sr, Ba) is performed with FP-LAPW technique. The A3SnO exhibit narrow direct band gap, in contrast to the wide indirect band gap of the respective perovskites. Hence, indirect to direct band gap transformation can be realized by the structural transition from perovskite to anti-perovskite. The p-p hybridization between A and O states result in the covalent bonding. The transparency and maximum reflectivity to the certain energies, and the verification of the Penn's model indicate potential optical device applications. Thermoelectric behaviors computed within 200–800 K depict that Ca3SnO exhibits good thermoelectric performance than Ba3SnO and Sr3SnO, and all three operate at their best at 800 K suggesting high temperature thermoelectric device applications.