Absolute Value Of Seebeck Coefficient Research Articles

Effect of single and dual doping on the thermoelectric properties of FeVSb0.95Sn0.05 and Fe0.95Co0.05VSb0.90Sn0.10 half-Heusler alloys

FeVSb in addition to a set of novel FeVSb0.95Sn0.05 and Fe0.95Co0.05VSb0.90Sn0.10 half-Heusler alloys were fabricated by arc melting followed by induction melting simple methods. Impacts of single Sn-doping and double Co- and Sn-doping on the structural and thermoelectric properties of FeVSb were investigated in this article. Structural and thermoelectric properties of FeVSb, FeVSb0.95Sn0.05 and Fe0.95Co0.05VSb0.90Sn0.10 compounds have been extensively studied in this work. N-type conduction was confirmed for the FeVSb system and for the doped FeVSb0.95Sn0.05 and Fe0.95Co0.05VSb0.90Sn0.10 alloys. The absolute value of Seebeck coefficient for the single Sn-doped sample increased from 127 μV/K to 155 μV/K, with the temperature increasing. Similarly, the Seebeck coefficient of the double Co- and Sn-doped alloy also increased from 40 μV/K to 60 μV/K. The thermoelectric power factor was notably enhanced for the dual doped Fe0.95Co0.05VSb0.90Sn0.10 alloy reaching 14 μW/cm.K2. Lattice thermal conductivity of the single Sn-doped FeVSb0.95Sn0.05 alloy decreased considerably over the whole temperature range. A maximum zT of 0.084 was achieved for FeVSb0.95Sn0.05 alloy at 575 K. The improved figure of merit due to doping is attributed to the phonon scattering at point defects. Sn-doping has significantly reduced thermal conductivity due to the enhanced point-defect and electron–phonon scatterings which contributed to improved thermoelectric figure of merit. Our findings showed also that the room-temperature thermal conductivity is seriously reduced via Sn and Co dual doping leading to higher ZT value for Fe0.95Co0.05VSb0.90Sn0.10 alloy. Promising candidates for further thermoelectric applications could be achieved by Sn-doping and double Co- and Sn-doping.

Isovalent co-alloying contributes to considerable improvement in thermoelectric performance of BiSe bulks with weak anisotropy

BiSe with intrinsic low thermal conductivity has considered as a promising thermoelectric (TE) material at nearly room temperature. To improve its low thermoelectric figure of merit (zT), in this work, Sb and Te isovalent co-alloying was performed and significantly optimized its TE property with weakly anisotropic characteristic. After substituting Sb on Bi sites, the carrier concentration is suppressed by introduction of Sb Se site defects, which contributes to the increased absolute value of Seebeck coefficient (|S|). Further co-alloying Te on Se of the optimized composition Bi0.7Sb0.3Se, the carrier concentration increased without affecting the |S| due to the enhanced effective mass, which leads to a highest power factor of 12.8 μW/(cm·K2) at 423 K. As a result, a maximum zT of ∼0.54 is achieved for Bi0.7Sb0.3Se0.7Te0.3 along the pressing direction and the average zT (zTave) (from 300 K to 623 K) are drastically improved from 0.24 for pristine BiSe sample to 0.45. Moreover, an energy conversion efficiency ∼4.0% is achieved for a single leg TE device of Bi0.7Sb0.3Se0.7Te0.3when applied the temperature difference of 339 K, indicating the potential TE application.

Comparative investigations of structural, electronic, optical, and thermoelectric properties of pure and 2 at. % Al-doped ZnO.

We comparatively investigate the properties of pure ZnO and 2 at. % Al doping concentration of ZnO, AZO, as potential candidates for specific applications. Calculations were carried out, using Wien2k package, to deduce structural, electronic, optical thermoelectric, and properties of both ZnO and AZO materials via the combination of GGA and mBJ approximations. It is shown that Al doping of ZnO (AZO) improves its optical properties; the deduced direct fundamental gap is enhanced due to the Burstein-Moss effect. Moreover, the dielectric function, at lower energies, confirms the existence of an extra strong fluctuation in the dispersive real part ɛ1(ω) and a high peak for absorptive imaginary parts ɛ2(ω) which are due to a variation in specific molecular bonding and the transition between the occupied and the non-occupied states. The critical point, observed at 2.81 eV for pure ZnO, is shifted to 3.3 eV in 2 at. % AZO, confirming a larger optical band gap. The reflectivity values slightly decreased for 2% AZO. The investigation of thermoelectric parameters as a function of chemical potential at different temperatures ranging from 300 to 900°C showed that these structures can be considered for good thermoelectric devices with (i) high absolute values of Seebeck coefficient: ׀SZnO׀ = 1.16 mV/K and ׀SAZO׀ = 0.746 mV/K, (ii) no effect of temperature on electrical conductivity but a strong effect on thermal conductivity, (iii) a high value approaching unity for the figure of merit. Hence, these properties and their improvements, introduced by Al doping of ZnO, lead specific and more uses in optoelectronics, energy, and piezoelectric applications.

Magnetism, electrical and thermal transport in R2Ni5C3 (R = La-Nd, Sm, Gd, Tb)

Ternary carbides R2Ni5C3 (R = La-Nd, Sm, Gd, Tb) are the only representatives of the family of interstitial carbides (i.e., compounds with the composition RxTyCz, where T is a transition metal and 2 ≤ (x + y)/z ≤ 4). The crystal structures (space group P4/mbm) of Sm2Ni5C3 [a = 8.26131(7) Å, c = 3.89090(4) Å, RB = 3.2 %, Rp = 1.3 %] and Gd2Ni5C3 [a = 8.24683(4) Å, c = 3.85398(2) Å, RB = 3.9 %, Rp = 3.6 %] are refined for the first time. They are considered to be built by distorted [R8]-cubes incorporating [CNi6]-octahedra condensed with [C2R8]-trigonal bi-prisms. The structural units are characteristic of the CaTiO3- and AlB2-prototypes, respectively. Temperature dependencies of the magnetic susceptibility, specific heat, electrical resistivity, thermal conductivity, and thermopower in the range 1.8 K (2 K) – 300 K are studied. R2Ni5C3 with R = Nd, Sm, Gd, order antiferromagnetically at TN = 3.4, 6.6, and 22.2 K, respectively. The nature of magnetic transitions in Ce2Ni5C3 at Tmag = 2.3 K and Tb2Ni5C3 at 29.4 K requires further clarification. No magnetic orderings for La2Ni5C3 (Pauli paramagnetic) and Pr2Ni5C3 (Curie-Weiss/van Vleck paramagnetic) are detected. Relatively high electrical resistivities and thermal conductivities, together with the small absolute values of Seebeck coefficients, result in poor thermoelectric performance of the R2Ni5C3 carbides. The calculated electronic structure for La2Ni5C3 indicated a rather low density of states at the Fermi level as well as its extreme sensitivity to any doping. The stabilization of the R2Ni5C3 interstitial carbides up to R = Tb is discussed assuming the rigid-band approach as well as the analysis of selected Ni-C interatomic distances.

Robustly Enhanced Seebeck Coefficient in the MXene/Organics/TiS2 Misfit Structure for Flexible Thermoelectrics.

The flexible thermoelectric (TE) generator has emerged as a superior alternative to traditional batteries for powering wearable electronic devices, as it can efficiently convert skin heat into electricity without any safety concerns. MXene, a highly researched two-dimensional material, is known for its exceptional flexibility, hydrophilicity, metallic conductivity, and processability, among other properties, making it a versatile material for a wide range of applications, including supercapacitors, electromagnetic shielding, and sensors. However, the low intrinsic Seebeck coefficient of MXene due to its metallic conducting nature poses a significant challenge to its TE application. Therefore, improving the Seebeck coefficient remains a primary concern. In this regard, a flexible MXene/organics/TiS2 misfit film was synthesized in this work through organic intercalation, exfoliation, and re-assembly techniques. The absolute value of Seebeck coefficient of the misfit film was significantly enhanced to 44.8 μV K-1, which is five times higher than that of the original MXene film. This enhancement is attributed primarily to the weighted effect of the Seebeck coefficient and possibly to energy-filtering effects at the heterogeneous interfaces. Additionally, the power factor of the misfit film was considerably improved to 77.2 μW m-1 K-2, which is 18 times higher than that of the original MXene film. The maximum output power of the TE device constructed of the misfit film was 95 nW at a temperature difference of 40 K, resulting in a power density of 1.18 W m-2, demonstrating the significant potential of this technology for driving low-energy consumption wearable electronics.

A novel n‐type poly(sulfonic acid diphenyl aniline) and its nanocomposites with large Seebeck coefficient enhanced with external magnetic fields

AbstractMost of the polymeric thermoelectric materials represent p‐type conductivity; however, those of n‐type are very few. We report some novel n‐type polymeric materials, which are poly(sulphonic acid diphenyl aniline) (PSDA) and its nanocomposites with polythiophene (PTh). They were synthesized in aqueous media using chemical oxidation polymerization process under the external magnetic field where the flux intensities are 0, 1.5, 2.5, and 4.6 kGauss. As the magnetic flux density increases, absolute values of Seebeck coefficient of PSDA and PSDA/PTh nanocomposite films increased however their conductivity did not changed. The negative sign of Seebeck coefficients indicated that PSDA and PSDA/PTh nanocomposites have n‐type conductivity. The highest Seebeck coefficient and power factor were obtained as −2535 μV/K and 0.031 μW/mK2, respectively, for PSDA synthesized under 4.6 kGauss magnetic flux. Changes of the Seebeck coefficient were examined in detail with XPS analysis. FTIR, UV–vis spectroscopy, DLS, and XRD analyzes were also performed for the characterization of the polymers. Their surface morphologies were examined by STEM.

Zr-based quaternary half-Heusler alloy systems ZrNimX0.5Sb1.5−m (X Fe/In): Studies on phase evolution, crystal structures and electronic properties

Half Heusler(hH) compounds have demonstrated exceptional capability in a wide range of functional applications as semiconductors. Although there are theoretical predictions about newer compounds and their thermodynamic stability, experimental validation is often missing. In this study, we report two quaternary multicomponent Zr-based hH alloy systems, namely ZrNi0.5Fe0.5Sb and ZrNiIn0.5Sb0.5, designed by combining 19 and 17 VEC (valence electron count) alloy systems. The structural features, including the crystal structures and compositions, were established using multiple techniques like X-ray diffraction, scanning and transmission electron microscopy. Both these systems crystallized in signature hH cubic structure (F43̅m) having lattice parameters 0.6091 nm and 0.6104 nm, respectively. The measurement of Seebeck coefficients over a wide temperature range showed p-to n-type semiconductor transition in ZrNi0.5Fe0.5Sb at around 888 K due to bipolar conduction. Subsequently, the partial substitution of Co for Fe sites (ZnNi0.5Fe0.3Co0.2Sb) completely suppressed the bipolar conductivity, making it a n-type semiconductor and increased the absolute value of Seebeck coefficient, by an order of magnitude, to − 133μV/K. The alloy ZrNiIn0.5Sb0.5 showed n-type semiconductor behavior throughout the measurement temperature range. This study conducts an in-depth examination of the microstructural phase evolution, chemical environment of the elements forming the novel hH phase and demonstrates the tunability of electronic properties through aliovalent substitutions at various lattice sites.

Thermoelectric properties of Cu‐Doped Heusler compound Fe2‐xCuxVAl

AbstractWe investigated the effects on thermoelectric properties of Cu doping in Fe2‐xCuxVAl at Fe site of full‐Heusler type compound. It is found that the Cu doping for Fe sites causes a significant increase in the absolute value of Seebeck coefficient |S| and a decrease in thermal conductivity. The Seebeck coefficient (S)=‐148μV/K and the Power factor (PF)=4.0 mWK−2m−1 have been observed for Fe1.9Cu0.1VAl (x=0.1) at 300 K. To further improve it, we fixed the Cu doping level at x=0.1 in Fe2‐xCuxVAl and co‐doped the material with Si at Al site, namely, Fe1.9Cu0.1VAl1‐ySiy. The thermoelectric properties have been improved by Si doping to a certain limit. We observed a decrease in electrical resistivity and lattice thermal conductivity by Si doping for Al. The maximum power factor of 4.5 mWK−2m−1 has been achieved for Fe1.9Cu0.1Al0.9Si0.1 at 350 K. More precisely, the thermoelectric performance has been improved with co‐doping of Cu for Fe sites and Si for Al sites. The largest ZT value is 0.13 for Fe1.9Cu0.1VAl1‐ySiy (y=0.15). Magnetic susceptibility suggests that all the measured compounds are showing paramagnetic behavior. The magnetic character is the most pronounced in Fe1.9Cu0.1VAl among the materials investigated, pointing to a possible correlation between the magnetic character due to electronic correlation and the larger Seebeck coefficient in this sample.

The prediction of electronic and thermoelectric performance of bulk and monolayer Sb2TeSeS

The thermoelectric (TE) properties of the bulk and monolayer Sb2TeSeS have been studied by the first-principles calculations and the Boltzmann Transport theory. Due to the greater band gap, the absolute values of Seebeck coefficient for TB-mBJ potential at the vicinity of Fermi level are larger than that for GGA approach. It is found that the electronic thermal conductivity of the layered structure of Sb2TeSeS is relatively lower than that of the bulk compounds. It is stable for monolayer Sb2TeSeS on account of the phonon structure without imaginary frequency, and the phonon dispersion is comparatively flatter. It is expected the ultra-low lattice thermal conductivity, which is verified by the result of the calculated lattice thermal conductivity. For monolayer Sb2TeSeS, the maximum value of figure of merit, which is procured from p-type doping within the reasonable range of carrier concentration, is larger than the optimal ZT value of other well-known materials. Therefore, p-type doping of monolayer Sb2TeSeS is a potential candidate for TE device applications.

Thermoelectric properties of tetragonal HfH2 under doping effect: First principles study

The effect of doping on the transport properties of HfH2 is explored using first-principles method and semi-classical Boltzmann approach. Thermoelectric properties such as electrical conductivity, Seebeck coefficient, electron and lattice thermal conductivity of doped and pure samples are calculated under various temperatures. The calculated results show that electrical and thermal conductivities increased with electron carrier concentrations similar to results reported by other studies in the low doping regime. While in the hole carrier concentration regime, irregular behavior is observed, especially in density of carriers equal to n = 4.6 × 1023 cm−3. Also, the lattice thermal conductivity and absolute value of Seebeck coefficient have been decreased with electron carrier concentration but these properties have irregular trend in the hole doping regime. Our results suggest that for achieving lower electron thermal conductivity with respect to pure HfH2, hole doping is much effective. Furthermore, the dispersive and large contribution of 5d orbital of Hf near the Fermi state and very low variation of L (Wiedemann-Franz factor) compared to the value of the free electron model L0, for pure and doped samples indicate that electrons in HfH2 have itinerant behavior and free-electron model is suitable to describe the transport properties of pure and doped samples of HfH2.

Synergistically Optimized Electrical and Thermal Transport Properties of CaMnO3 via Doping High Solubility Sr

Herein, we show that we can synergistically optimize the electrical and thermal transport properties of CaMnO3 via doping Sr. All the samples exhibit a single phase with an orthorhombic symmetry within the experimental doping range (0-10%). Sr doping significantly reduces resistivity while maintaining a relatively high absolute value of Seebeck coefficient, resulting in an effective enhancement in the electrical properties of the material. The maximum power factor (∼ 3.01 μ W cm−1 K−2) is achieved at 873 K for Ca0.96Sr0.04MnO3, which is three times larger than that of the un-doped CaMnO3. The thermal conductivity governed by lattice thermal conductivity is notably decreased compared with the un-doped sample, which is mainly attributed to the decreased grain size and large mass and strain fluctuations caused by Sr doping, and the thermal conductivity decreases with increasing Sr doping level. The enhanced power factor and significantly reduced thermal conductivity lead to a maximum ZT value of 0.15 at 873 K in the Ca0.90Sr0.10MnO3 sample, indicating that CaMnO3 is a potential candidate for high-temperature application.

Significant Enhancement in the Thermoelectric Performance of Aluminum-Doped ZnO Tuned by Pore Structure.

In this paper, 2 atom % Al-doped ZnO (AZO) was prepared by the co-precipitation method together with sparking plasma sintering (SPS) treatment. The as-synthesized AZO powders show the morphology of hollow hexagonal towers, which result in a high porosity of 50.6% in the bulk sample consolidated by SPS sintering at 400 °C, and the porosity decreases gradually with increasing sintering temperature up to 1000 °C. Positron annihilation measurements reveal that even after sintering at 1000 °C, there are still a considerable number of small pores. A high electrical conductivity of 3 × 105 S m-1 is achieved at room temperature for the AZO sample sintered at 1000 °C, while the absolute values of Seebeck coefficient keep at relatively high values between 59 and 144 μV K-1 in the measurement temperature range of 27-500 °C, leading to a high power factor of 3.4 × 10-3 W m-1 K-2. On the other hand, the pores in AZO act as strong phonon scattering centers, and an extremely low thermal conductivity of 1.5 W m-1 K-1 measured at room temperature is obtained for AZO sintered at 400 °C. Due to the residual pores in the 1000 °C-sintered sample, the thermal conductivity is still relatively low. As a result, a maximum ZT of 0.275 measured at 500 °C is obtained in this sample, which is the highest ZT reported for ZnO around this temperature.

The microstructure and thermoelectric properties of the Mg2(Sn,Si,Bi) films containing excess metal Mg phase

To avoid the uncontrollable Mg content in deposited films caused by the easy evaporation of Mg in alloy target, the Mg2(Sn,Si,Bi) solid solutions films with a tiny of excess Mg metal phase were prepared using a Mg-Sn-Si-Bi alloy target and a high pure Mg target by magnetron sputtering alternately. The phase components, microstructures as well as the thermoelectric properties were systematically investigated. The excess metal Mg phase with a few micron size uniformly distributes in the Mg2(Sn,Si,Bi) solid solution films and the size of the excess metal Mg phase becomes bigger and bigger and the phase gradually convert a narrow strip shape as Mg target sputtering time increase from 40 to 60 s. It is beneficial to an increase in both Seebeck coefficient and electrical conductivity that a tiny excess metal Mg phase exists in Mg2(Sn,Si) based films. The Mg2(Sn,Si) based films containing tiny excess metal Mg phase with an appropriate size posses the highest absolute value of Seebeck coefficient and appropriate electrical conductivity, resulting in the maximum power factor.

Anisotropic thermoelectric effect and field-effect devices in epitaxial bismuthene on Si (111)

This experimental study reveals intriguing thermoelectric effects and devices in epitaxial bismuthene, two-dimensional (2D) bismuth with thickness ⩽30 nm, on Si (111). Bismuthene exhibits interesting anisotropic Seebeck coefficients varying 2–5 times along different crystal orientations, implying the existence of a puckered atomic structure like black phosphorus. An absolute value of Seebeck coefficient up to 237 μV K−1 sets a record for elemental Bi ever measured to the best of our knowledge. Electrical conductivity of bismuthene can reach up to 4.6 × 104 S m−1, which is sensitive to thickness and magnetic field. Along with a desired low thermal conductivity ∼1.97 W m−1 K that is 20% of its bulk form, the first experimental zT value at room temperature for bismuthene was measured ∼10–2, which is much higher than many other VA Xenes and comparable to its bulk compounds. Above results suggest a mixed buckled and puckered Bi atomic structure for epitaxial 2D bismuth on Si (111). Our work paves the way to explore potential applications, such as heat flux sensor, energy converting devices and so on for bismuthene.

Transport and thermoelectric properties of (Sr1−xEux)3Ti2O7

The transport and thermoelectric properties of polycrystalline bulk samples (Sr1−xEux)3Ti2O7 with different Eu-doped contents x were investigated. The experiments revealed that electrical resistivity ρ and the absolute value of Seebeck coefficient |S| decreased as x increased from 0.05 to 0.1 at temperatures ranging from 300 to 1000 K. However, electrical resistivity ρ increased instead when x further increased from 0.1 to 0.15, whereas |S| dropped below 450 K and then rose above 450 K. |S| for (Sr1−xEux)3Ti2O7 (x = 0.05, 0.1) increased linearly in tandem with an increase in temperature, whereas |S| for (Sr1−xEux)3Ti2O7 (x = 0.15) increased first, decreased next, and finally increased in tandem with an increase in temperature. The abnormality of |S| with temperature for (Sr0.85Eu0.15)3Ti2O7 may be attributed to the existence of mixed conduction in this sample. Moreover, mobile charge-carrier thermal conductivity is somewhat negligible compared with that of phononic contribution, suggesting that phonon contribution is predominant in these oxides. Thermal conductivity κ for all compounds decreased gradually with increasing temperature. The dimensionless figure of merit (ZT) values of Eu-doped compounds increased with an increase in temperature. The maximum ZT is 0.061, which was obtained in compound (Sr0.9Eu0.1)3Ti2O7 at 1000 K.

Formation and properties of high entropy oxides in Co-Cr-Fe-Mg-Mn-Ni-O system: Novel (Cr,Fe,Mg,Mn,Ni)3O4 and (Co,Cr,Fe,Mg,Mn)3O4 high entropy spinels

Possibility of formation of quinary and senary equimolar high entropy oxides from the Co-Cr-Fe-Mg-Mn-Ni-O system is presented. Different proposed compositions are synthesized using the solid-state reaction route at high temperatures (900−1100 °C) and quenched to room temperature. Phase composition of the samples is studied, showing tendency toward formation of two main phases: rock salt-structured Fm-3 m and spinel-structured Fd-3 m. It is documented that the annealing temperature has a profound effect on stability of both structures, and at 1100 °C usually the highest content of Fm-3 m phase is usually observed. Three different oxides, namely, (Co,Cr,Fe,Mn,Ni)3O4, (Co,Cr,Fe,Mg,Mn)3O4 and (Cr,Fe,Mg,Mn,Ni)3O4 are obtained as single-phase materials, which structure can be described as the high entropy Fd-3 m spinel one. The latter two compounds have not been previously reported in the literature. Activated character of the electrical conductivity dependence on temperature is observed, with relatively high total conductivity at high temperatures and corresponding high absolute values of Seebeck coefficient.

Synthesis of FeVSb1−xSex Half-Heusler Alloys via Mechanical Alloying and Evaluation of Transport and Thermoelectric Properties

Se-doped half-Heusler compositions, FeVSb1−xSex (0.03 ≤ x ≤ 0.15), were fabricated by mechanical alloying followed by vacuum hot pressing. The goal of this synthesis was to explore the effect of Se doping on the thermoelectric and transport properties of FeVSb system. A near single half-Heusler phase was found to form; however, a second phase of FeSb2 couldn’t be avoided in this process. N-type conduction was confirmed and Se acted as a donor for the FeVSb system. Lattice thermal conductivity also considerably decreased after Se doping. The absolute value of Seebeck coefficient is increased to a maximum of 126 μVK−1 at 956 K for x = 0.12, which may help to increase the figure of merit (ZT) of the FeVSb system. The figure of merit is improved by Se doping, and the improvement is possibly owing to the combined effect of fine grain structure, increased effective mass and phonon scattering at the grain boundaries. A maximum ZT of 0.27 was achieved for FeVSb0.88Se0.12 at 847 K.

Enhanced thermoelectric property of nanostructured CaMnO3 by sol-gel hydrothermal method

Perovskite CaMnO3 nanoparticles were synthesized by sol-gel hydrothermal method at 200 °C, and the samples were annealed at different temperatures between 800 °C and 1000 °C in steps of 50 °C under oxygen (CaMnO3) and air (CaMnO2.5) atmosphere. The systematic analysis revealed the annealing temperature and atmosphere influenced significant changes in the crystal structure, crystallite size, and oxygen stoichiometry of the material. Powder XRD analysis showed that stable orthorhombic perovskite structure acquired at 950 °C. Microstructure studies confirmed that grains were spherical, and larger grain size was observed for higher annealing temperature. Raman spectra determined orthorhombic domains and the symmetry of Raman lines. Negative values of thermopower were observed, and absolute Seebeck coefficient value for CaMnO3 and CaMnO2.5 was found to be −312 μVK−1 and -287 μVK−1 at room temperature. Stoichiometric CaMnO3 nanoparticle is a suitable material for thermoelectric applications due to low activation energy and high power factor.

Enhanced TE properties of Cu@Ag/Bi2Te3 nanocomposites by decoupling electrical and thermal properties

Cu@Ag/Bi2Te3 nanocomposites were prepared for the first time by ultrasonic dispersion-rapid freeze-drying method combined with spark plasma sintering (SPS). By changing the content of Cu@Ag nanoparticle, we could modulate the temperature dependent thermoelectric properties. The highest ZT value can be obtained at 450 K for 1 vol% Cu@Ag/Bi2Te3, which is benefited from the decoupling of electrical and thermal properties. With the increase of electrical conductivity, the absolute value of Seebeck coefficient lifts while the thermal conductivity declines. Meanwhile, the average ZT value between 300 K and 475 K was 0.61 for 1 vol% Cu@Ag/Bi2Te3, which is much higher than that of pristine Bi2Te3. Therefore, the decoupling effect of Cu@Ag nanoparticles incorporation could be a promising method to broaden the application of Bi2Te3 based thermoelectric materials.

Thermoelectric Properties of Reduced Graphene Oxide/Bi2Te3 Nanocomposites

Reduced graphene oxide (rGO)/Bi2Te3 nanocomposite powders with different contents of rGO have been synthesized by a one-step in-situ reductive method. Then, rGO/Bi2Te3 nanocomposite bulk materials were fabricated by a hot-pressing process. The effect of rGO contents on the composition, microstructure, TE properties, and carrier transportation of the nanocomposite bulk materials has been investigated. All the composite bulk materials show negative Seebeck coefficient, indicating n-type conduction. The electrical conductivity for all the rGO/Bi2Te3 nanocomposite bulk materials decreased with increasing measurement temperature from 25 °C to 300 °C, while the absolute value of Seebeck coefficient first increased and then decreased. As a result, the power factor of the bulk materials first increased and then decreased, and a power factor of 1340 μWm−1K−2 was achieved for the nanocomposite bulk materials with 0.25 wt% rGO at 150 °C.