Seebeck Coefficient Measurements Research Articles

A New Laser-Combined H-Type Device Method for Comprehensive Thermoelectrical Properties Characterization of Two-Dimensional Materials.

Two-dimensional nanomaterials have obvious advantages in thermoelectric device development. It is rare to use the same experimental system to accurately measure multiple thermoelectrical parameters of the same sample. Therefore, scholars have developed suspended microdevices, T-type and H-type methods to fulfill the abovementioned requirements. These methods usually require a direct-current voltage signal to detect in Seebeck coefficient measurement. However, the thermoelectric potential generated by the finite temperature difference is very weak and can be easily overwritten by the direct-current voltage, thereby affecting the measurement accuracy. In addition, these methods generally require specific electrodes to measure the thermoelectric potential. We propose a measurement method that combines laser heating with an H-type device. By introducing a temperature difference in two-dimensional materials through laser heating, the thermoelectric potential can be accurately measured. This method does not require specific electrodes to simplify the device structure. The thermoelectrical parameters of supported graphene are successfully measured with this method; the results are in good agreement with the literature. The proposed method is unaffected by material size and characteristics. It has potential application value in the characterization of thermoelectric physical properties.

Ternary system based on polyaniline, graphene, and acrylic matrix applied to thermoelectric systems

AbstractThermoelectric (TE) materials have attracted attention for offering a green option for power generation, due to their ability to convert thermal energy into electricity. In recent years, a promising way to achieve efficiency in TE properties has been proposed based on composites of conjugated polymers, such as polyaniline (PANI), and carbon nanomaterials such as graphene (GR). Since polyaniline and GR composites are promising fillers for organic thermoelectric materials (OTE), we expanded their investigations for a ternary system (TS), providing materials with multiple functionalities, and high performance. In this research work, a TS based on an acrylic matrix (ACR), GR, and PANI was successfully prepared through the combination of in situ polymerization of aniline in contact with GR and mechanical mixture of the resulting hybrid with an ACR. Structural and morphological characterization confirmed that GR affected PANI morphology and crystallinity. The band gap determination by Tauc's relation indicated the occurrence of π‐π interaction between the chains and an increase of the electrical conductivity of the composites allowed to infer a synergistic effect. The measured Seebeck coefficient reached a maximum value of −17.02 μVK−1 and the highest power factor obtained was 4.94 μWm−1 K−2 for the ACR/PANI sample, indicating a material with promising thermoelectric properties.

Dopant induced band convergence leading to high thermoelectric power factor in Mg2Sn

Band convergence is a common technique for enhancing the power factor of thermoelectric (TE) materials. This is usually achieved by solid solution formation in compounds having specific electronic band features. In this work, we show that a similar band convergence effect can be achieved in Mg2Sn by doping with small amounts of Bi. To identify this effect and the possible reason behind it, a detailed investigation of the electronic band structure (EBS) has been carried out using a recently developed multi-band refinement technique (MBRT). Nominal compositions of Mg2.2Sn1-xBix (x = 0,0.005, 0.01, 0.0125, 0.015, 0.02) have been synthesized by induction melting followed by compaction using uniaxial hot-pressing. Measurement of Seebeck coefficient (S), electrical conductivity (σ) and Hall Coefficient (RH) have been performed between 300K–700K and the data used for multi-band refinement. Results indicate changes in the inter-band separation of conduction bands with doping content and temperature. Significantly lower inter-band separation compared to reported undoped data is found even for the lowest doped composition, resulting in both conduction bands contributing to the power factor (S2σ). Further, for the heavily doped compositions (x = 0.0125, 0.015, 0.02) band-flipping between the conduction bands has been observed. Thus, the light conduction band is found to constitute the conduction band edge in the heavily doped compositions. This is contrary to the reported EBS of undoped Mg2Sn in which the heavy conduction band has a lower energy. Also, increasing temperature results in band convergence in the heavily doped compositions. A plausible cause for the band-flipping behaviour is provided based on merging of the impurity band with the light conduction band in heavily doped Mg2Sn. The band-flipping and the subsequent band convergence results in an even higher S2σ in the heavily doped compositions. The work highlights the beneficial influence of Bi doping on the TE properties of Mg2Sn and opens the possibility of utilizing dopants for achieving band convergence in TE materials.

Measurements of electrical resistivity and Seebeck coefficient for disc-shaped samples

Herein we develop a methodology to measure the resistivity of discs by deriving a mathematic formula between resistivity and resistance from solving the electrostatic Laplace equation in polar coordinates. Then the resistivity and Seebeck coefficient of disc samples of p- and n-type bismuth telluride are measured experimentally either in nitrogen or helium atmosphere. The validity of Seebeck coefficient is demonstrated by the excellent linearity between Seebeck voltages and temperature differences. The bar samples are also measured for comparison. Finite element simulation is utilized to display the two-dimensional potentials and currents and have an error analysis. Furthermore, the resistivity error due to the probe distance error is discussed analytically based on the mathematic formula, and the probe distance can be optimized to minimize the resistivity error. The disclosed approach would extend the applicability of the present instruments to the disc-shaped samples and be useful in the emerging transverse thermoelectricity.

Thermoelectric properties of Ga-doped InSb alloys

Internal structure and thermoelectric properties of In1-xGaxSb alloys, prepared by melting synthesis at 1123 K, were systematically studied in this paper. Crystal structure was investigated by XRD analysis. All samples exhibited crystalline structure of single InSb phase. Transport and electrical properties were studied against temperature elevating. Electrical conductivity was determined via the standard four probe method. The thermal behavior of the electrical conductivity over the temperature range between 273 K and 473 K showed semiconducting behavior. Seebeck coefficient measurements were conducted via differential method in the temperature range 273–473 K. The measurements of Seebeck coefficient confirmed the electrical conductivity behavior of the samples. The maximum obtained Seebeck coefficient value |S| of the parent InSb compound was observed at 224 μV/K, obtained at 273 K. The alloy has been doped with Ga in order to enhance thermoelectric properties. Results showed that introducing of Ga into In sites leads to significant increase in the Seebeck coefficient up to 330.4 μV/K. Power factor was estimated from the measurements of the electrical conductivity and the Seebeck coefficient. Interesting enhancement in the thermoelectric power factor was observed with Ga-doping. The maximum power factor was obtained for the most doped sample exhibiting 2.3 μWm−1 K−2 at 273 K. The thermal conductivity was obviously reduced by substituting In with Ga. The dimensionless figure of merit was estimated showing an enhancement with the Ga addition. The maximum recorded ZT was 0.017 observed at 403 K.

Ionic thermoelectric effect in Cu2-δSe during phase transition

The ionic Seebeck coefficient was studied in copper selenide with Cu1.99Se, Cu1.95Se and Cu1.8Se stoichiometry which was synthesized with a melt crystallization method. To measure the ionic Seebeck coefficient of copper ions, 0.15C6H12N4CH3I + 0.85CuI solid-state electrolyte was prepared. Electrolyte layers were pressed with copper selenide powder into a sandwich-like structure. At the temperature of 410 K, the materials have ionic Seebeck coefficient values close to each other, about 1100 μV/K. In the case of β-phase structure (Cu1.8Se material), changes in the measured Seebeck coefficient were observed—with decreasing temperature, the ionic thermopower firstly increased reaching about 1230 μV/K and then decreased to 950 μV/K at 355 K. In the Cu1.99Se material, a phase transition to the α-phase was observed during cooling. The ionic Seebeck coefficient values gradually increased from 1030 to 1220 μV/K at 370 K, when the material is in the low-temperature phase. The measured difference between the ionic thermopower of the two phases well matches calculations based on the entropy of the transition (presence part of the Seebeck coefficient) and different activation energies of ionic transport (transport part).Graphical abstract

Unveiling transport properties in rare-earth-substituted nanostructured bismuth telluride for thermoelectric application

Abstract Thermoelectrics is an emerging technology in the field of renewable energy sources, and the exploration of doped materials has opened up new avenues for enhancing their performance. La-doped thermoelectric materials with the composition Bi2−x La x Te3 (x = 0.0, 0.1, 0.2, 0.3, 0.4) were synthesized using the WOWS sol–gel method and sintered at 500 °C for 5 h. X-ray diffraction analysis confirmed a rhombohedral crystal structure with lattice constants of a = b = 4.41(2) Å and c = 29.81(3) Å. Scanning electron microscopy revealed particle-like shapes (0.7–2.5 μm). Fourier transform infrared spectroscopy confirmed the single-phase nature of the samples. DC electrical measurements showed increasing conductivity with temperature. AC electrical analysis demonstrated frequency-dependent behavior with increasing AC conductivity and decreasing loss factor and dielectric constants. Seebeck coefficient measurements exhibited temperature-dependent behavior. Thermal transport properties showed increasing thermal conductivity and volumetric specific heat with temperature, while thermal diffusivity decreased. The composition Bi1.9La0.1Te3 with x = 0.1 doping displayed lower thermal conductivity, higher electrical conductivity, and a higher ZT value, making it more suitable for thermoelectric applications. Furthermore, the sample Bi1.8La0.2Te3 exhibited favorable characteristics for energy storage applications compared to the other samples. These findings provide insights into the potential applications of La-doped bismuth telluride compounds in thermoelectric and energy storage systems.

An Automatic Apparatus for Simultaneous Measurement of Seebeck Coefficient and Electrical Resistivity

A fully automated experimental system was designed for simultaneous measurement of the Seebeck coefficient and electrical resistivity of thermoelectric materials in bulk form. The system incorporates a straightforward and easily fabricated sample holder along with commercially available electronic instrument components. The sample holder showcases a compact design that utilizes two Peltier module heaters to induce sample heating and generate the required temperature gradient. System automation and control are achieved through the implementation of a LabView program. The Seebeck voltage and resistance of the sample (under specified temperature conditions) are determined using I–V measurements. The Seebeck voltage and resistance of the sample correspond to the intercept and slope of the I–V characteristic diagram in the four-point probe method, respectively. To verify the accuracy and reliability of the developed apparatus, a variety of experiments were performed on N-type and P-type bismuth telluride samples. The measurement results closely matched those obtained from commercial systems, with an overall data difference of less than 10% for both the Seebeck coefficient and resistivity measurements.

Tuning and interpretation of electronic transport properties with

Electronic transport coefficients such as the electrical conductivity, the termo-power, and the charge carrier concentration are routinely measured in a variety of application areas such as electronics or thermoelectric power-generation and cooling. Using fitting procedures, those measurements are used to infer microscopic features of the samples. The code ▪ facilitates the estimation of electronic structure parameters such as the effective masses and band energies improving the current approach by increasing the complexity of the band structure representation. The software is designed with a server-client architecture to enhance performance and scalability. The server is implemented in the Julia programming language. We illustrate the design and the efficiency of the code with selected applications, which are relevant to the optimization of thermoelectric materials. Program summaryProgram Title:▪CPC Library link to program files:https://doi.org/10.17632/494nj6ftbv.1Developer's repository link:https://github.com/marcofornari/etransport.gitLicensing provisions: GPLv3Programming language: Julia, Python.Nature of problem: Electronic transport measurements are routinely used to link the functional properties exploited in electronics and energy sciences applications with the underlying electronic structure of the material under investigation. Experimentalists collect data of derived and integrated physical quantities, from which they estimate properties and parameters, e.g., nature of the conduction mechanisms and effective mass. The interpretation is based on simplistic models that rarely represent the complexity of the band structure. The code ▪ improves the current state of the art and facilitates the estimation of effective masses and energies from experimental measurements of electrical conductivity, Seebeck coefficients, and carrier concentration using a multi-valley anisotropic parabolic band structure as a model for the unknown real band structure. Experimental data can be imported and visualized to facilitate the comparison with theoretical analysis.Solution method: The Boltzmann equation within the relaxation-time approximation is used to compute the electronic transport tensors from the electronic density of states characterized in terms of a set of effective masses tensors mi⁎ and critical energies ϵi. Numerical and analytical techniques are adopted to integrate the Boltzmann equation efficiently. By tuning the features of the density of states, temperature, Fermi level, and the functional expression for the relaxation time, the software streamlines the reconstruction of the underlying electronic properties from experimental data.Additional comments including restrictions and unusual features: The software is designed with a server-client architecture to enhance performance and scalability. The server is implemented in the Julia programming language as a stand-alone library. It performs all the numerical operations to compute the transport tensors from a set of multi-valley parabolic band structures. The client is implemented either as a command-line user interface (CLI) or a graphical user interface (GUI) written in the Python programming language. The communications between the server and clients are handled by a REST API, where the data are exchanged using JSON payloads.

Structural, electrical and optical properties of samarium fluoride doped SnO2 transparent conducting oxide thin films for optoelectronic device applications

In this study, p-type transparent tin oxide (SnO2) based semiconductor thin films were deposited onto glass substrates by sol-gel dip-coating method using samarium-trifluoride (SmF3) as acceptor dopant. The films were prepared by co-doping 2 mol.% of SmF3 into SnO2 (SFTO), followed by annealing temperature at 475 °C. XRD analysis results showed that the films exhibited the tetragonal rutile SnO2 phase. The p-type conductance of the SFTO films were confimed by Hall effect and Seebeck coefficient measurements. Resistivity and mobility of the SmF3 doped SnO2 film is 7.83 × 10–3Wcm and 7.57 cm2 V–1 s–1, respectively, which reduce in comparing with those of un-doped SnO2 film. Carrier concentration is large increase from –9.34 ´ 1018 cm–3 for un-doped- to +1.05 × 1020 cm–3 for SmF3 doped-SnO2 film. The p-type SFTO film showed a high transmittance of 74.3% at 550 nm, with band gap energy of 3.63 eV. Furthermore, a transparent p-SnO2:SmF3/n-ZnO:Al (Al doping level of 2 mol.%) heterojunction was fabricated on alkali-free glass substrates. The I-V curve measurement for the p-n heterojunction diode showed a typical rectifying characteristic with a forward turn-on voltage of 1.55 V. With obtained properties, the p-type SFTO film holds great promise for optoelectronic devices applications.

Accelerated measurement of electrical resistivity and Seebeck coefficient for thin-layer thermoelectric materials

Compared to the diffusion couple and thin film material library, the thin-layer (also known as thick film) material library with discrete compositions is more suitable for the screening of high performance thermoelectric (TE) materials. However, there are few apparatuses for high throughput characterizing TE properties of thin-layer material library. In this work, a tool with high reliability for effectively and quickly measuring electrical resistivity and Seebeck coefficient has been successfully developed via using a combination of van der Pauw and quasi-steady state method. The relative measurement errors of the electrical resistivity and Seebeck coefficient are less than 10%, comparable to commercial ZEM-3 equipment. The time to measure the electrical resistivity and Seebeck coefficient at a single temperature point is 4 min, saving up to 61.8% of the time compared to ZEM-3. This will contribute to the screening of novel TE materials from the thin-layer TE material libraries in the future.

Effect of Thickness Variation on the Measured Seebeck Coefficient and Power Factor in ITO–NiCr Thin‐Film Thermocouples

Herein, the electrical resistivity, Seebeck coefficient, and power factor of an indium tin oxide (ITO) and nickel‐chromium (NiCr) thermocouple are investigated. The thicknesses of the ITO and NiCr are varied between 10 and 430 nm. Seebeck coefficients between 12.8 and (21.4 ± 1.5) μV K−1 are measured, respectively. The results indicate that a reduction in thickness generally leads to an increase in the Seebeck coefficient until a maximum value is reached. Among the measured samples, the optimal Seebeck coefficients are found with an ITO thickness of (111 ± 4) nm and NiCr thickness of (18 ± 2) nm. Finally, the power factor of the thermocouples is determined, with a maximum power factor of (84 ± 7) μW m−1 K−2 for the ITO thickness of (111 ± 4) nm and nickel‐chromium thickness of (42 ± 5) nm.

Magnetic and transport properties in metallic and disordered Ru2VAl and Ru2VGa

In this work, we report an elaborate study on the structural, magnetic and thermoelectric properties of two Ru-based Heusler alloys, viz., Ru2VAl and Ru2VGa, having valence electron count 24. While Ru2VGa exhibits a nonmagnetic ground state, in Ru2VAl a short range ferromagnetic interaction is developed below 10 K due to the structural antisite defects and disorder, that also manifests its signature in the specific heat and electrical resistivity measurements at low temperatures. Both the Seebeck coefficient (S) and Hall measurements suggest the dominance of hole-type carrier for electronic transport in Ru2VAl whereas Ru2VGa is found to be a n-type material. The linear nature and small absolute values of S, as well as non-zero values of electronic contribution to specific heat γS (γSRu2VAl = 4.9 mJ/mol-K2 and γSRu2VGa = 5.5 mJ/mol-K2) point towards a metallic ground state for both these alloys. Both the compounds exhibit lower thermal conductivity at room temperature in comparison to Fe-based Heusler alloys due to the presence of heavier element Ru.

Surface Chemistry and Band Engineering in AgSbSe2: Toward High Thermoelectric Performance.

AgSbSe2 is a promising thermoelectric (TE) p-type material for applications in the middle-temperature range. AgSbSe2 is characterized by relatively low thermal conductivities and high Seebeck coefficients, but its main limitation is moderate electrical conductivity. Herein, we detail an efficient and scalable hot-injection synthesis route to produce AgSbSe2 nanocrystals (NCs). To increase the carrier concentration and improve the electrical conductivity, these NCs are doped with Sn2+ on Sb3+ sites. Upon processing, the Sn2+ chemical state is conserved using a reducing NaBH4 solution to displace the organic ligand and anneal the material under a forming gas flow. The TE properties of the dense materials obtained from the consolidation of the NCs using a hot pressing are then characterized. The presence of Sn2+ ions replacing Sb3+ significantly increases the charge carrier concentration and, consequently, the electrical conductivity. Opportunely, the measured Seebeck coefficient varied within a small range upon Sn doping. The excellent performance obtained when Sn2+ ions are prevented from oxidation is rationalized by modeling the system. Calculated band structures disclosed that Sn doping induces convergence of the AgSbSe2 valence bands, accounting for an enhanced electronic effective mass. The dramatically enhanced carrier transport leads to a maximized power factor for AgSb0.98Sn0.02Se2 of 0.63 mW m-1 K-2 at 640 K. Thermally, phonon scattering is significantly enhanced in the NC-based materials, yielding an ultralow thermal conductivity of 0.3 W mK-1 at 666 K. Overall, a record-high figure of merit (zT) is obtained at 666 K for AgSb0.98Sn0.02Se2 at zT = 1.37, well above the values obtained for undoped AgSbSe2, at zT = 0.58 and state-of-art Pb- and Te-free materials, which makes AgSb0.98Sn0.02Se2 an excellent p-type candidate for medium-temperature TE applications.

Physical properties of the full Heusler-type Ru2-Fe NbAl (x = 0.00–0.50) alloys

We report the physical properties of a series of full Heusler-type Ru2-xFexNbAl (x = 0.00–0.50) alloys using magnetization, electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) measurements. Structure and phase analysis via x-ray diffraction and scanning electron microscopy indicate that Fe replaces the Ru in Ru2NbAl, and the antisite disorders reduce. The dc magnetization shows predominantly paramagnetic behavior for all Fe-doped samples, as in the pristine Ru2NbAl sample. Interestingly, the electrical resistivity measurements reveal that the conduction behavior of Ru2NbAl alloy changes from semiconducting-like to metal-like with Fe substitution. In addition, a minimum in resistivity at low temperatures is observed in the Fe-doped samples. It is noted that the minimum shifts to low temperatures with Fe content, presumably due to the weak localization effect. The Seebeck coefficient measurements show that charge carriers of these alloys remain hole type with a maximum S value of ∼27 µV/K at 300 K for x = 0.13, a result of the modification of the electronic band structure. The Fe substitution is found to reduce thermal conductivity significantly. An analysis of the lattice thermal conductivity indicates that the reduction in κ is primarily due to more grain boundaries, Umklapp phonons, and electron scatterings. These observations lead to an increase in the thermoelectric performance, i.e., the figure of merit and power factor, to about 0.007 and 1.7 μW/cm K2 at 300 K for the optimized composition of Fe with x = 0.13.

Impacts of Annealing Temperature and Time on the Thermoelectric Performance of Recycled Carbon Fiber (RCF)/n-Bi2Te3 Heterostructure Thermoelectric Composites

Recycling carbon fibre waste is crucial for sustainability in the composites industry. Herein, we report the fabrication of a heterostructure composite using recycled carbon fiber (RCF) and n-type bismuth telluride (n-Bi2Te3) for thermoelectric applications. In the present study, we have comprehensively investigated the effects of annealing temperature and time on the thermoelectric, structural, charge carrier transport, morphological, and thermal stability properties of annealed RCF/n-Bi2Te3 composites. The optimum annealing temperature and time were at 350 °C and 2 h, respectively, which yielded a maximum power factor of 7.83 μWK−2m−1. Annealing redistributed the bismuth and tellurium atomic percentage, decreased carrier concentration, improved carrier mobility, enhanced the crystallinity and increased the grain size of the bismuth telluride particles, subsequently improving the thermoelectric performance as well as the thermal stability of annealed RCF/n-Bi2Te3 composites. In addition, this study has explored the plausibility of a cross-plane configured Seebeck coefficient measurement utilizing recycled carbon fibre/n-type bismuth telluride heterostructure thermoelectric composite. Energy band diagram analysis indicated favorable heterojunction alignment between RCF and n-Bi2Te3, validating the viability of the thermoelectric composite in a cross-plane configuration. Our study provides a promising route for closing the recycling loop of carbon fiber waste and achieving sustainable thermoelectric materials.

Improving the Performance of Layer-by-Layer Processed Organic Solar Cells via Introducing a Wide-Bandgap Dopant into the Upper Acceptor Layer.

The layer-by-layer (LbL) solution-processed organic solar cells (OSCs) are conductive to achieve vertical phase separation, tunable donor-acceptor (D/A) interfaces, and favorable charge-transport pathways. In this work, a wide-bandgap component poly(9-vinylcarbazole) (PVK) is added to the upper electron acceptor layer to improve the performance of LbL-processed OSCs. Results show that the PVK component can adjust the film morphology, dope the electron acceptor, increase the electron concentration, and improve charge transport. Such n-type doping is verified by Seebeck coefficient measurement, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance characterization. In addition, the fluorescence intensity and exciton lifetime of the PVK-doped acceptor film are increased, thus being beneficial for exciton diffusion to the D/A interface. Therefore, the power conversion efficiency (PCE) of LbL OSCs increases when 2.50 wt.% PVK is employed in the electron acceptor layer of commonly-used high-efficiency system and a maximum value of 19.05% can be achieved. The role of PVK played in the active layer is different from those of additives and ternary components reported previously, so the results provide an alternative way to enhance the device performance of LbL-processed OSCs.

The role of hetero-interface structures in enhancing the power factor of Cu2Se/x% Y2O3 composite thermoelectric materials

In this study, we have investigated the structural, thermal, electrical, and mechanical properties of the composite system Cu2Se/x% Y2O3 (0 ≤ x ≤ 1.00) as a function of varying Y2O3 concentration, x. The successful incorporation of Y2O3 in the Cu2Se matrix is carried out using the solid-state reaction method, and the same is confirmed by X-ray diffraction analysis. Due to the low concentration of Y2O3, all the prepared composites exhibit monoclinic crystal structure with P2/m space group within the X-ray detection limit at room temperature. The oxidation state of the studied composites is investigated using X-ray photoelectron spectroscopy (XPS). The composites exhibit an increase in mechanical hardness as a function of Y2O3 concentration, whereas the electrical resistivity shows no systematic variation with Y2O3 concentration. The highest resistivity is observed for the sample with x = 1%. The measured Seebeck coefficient (S) value increases with increasing temperature. The positive values of S indicate that the positive charge carriers (holes) dominate the thermoelectric transport. The thermal conductivity of the composites increases as compared to the Cu2Se pristine sample. The overall power factor and ZT of studied composites were found to decrease with the addition of Y2O3 to the Cu2Se system.

Experimental evidence of a size-dependent sign change of the Seebeck coefficient of Bi nanowire arrays

The electrical transport in bismuth nanowires is strongly influenced by both sample geometry and crystallinity. Compared to bulk bismuth, the electrical transport in nanowires is dominated by size effects and influenced by surface states, which gain increasing relevance with increasing surface-to-volume ratios, i.e. with decreasing wire diameter. Bismuth nanowires with tailored diameter and crystallinity constitute, therefore, excellent model systems, allowing to study the interplay of the different transport phenomena. Here, we present temperature-dependent Seebeck coefficient and relative electrical resistance measurements of parallel bismuth nanowire arrays with diameters between 40 and 400 nm synthesized by pulsed electroplating in polymer templates. Both electrical resistance and Seebeck coefficient exhibit a non-monotonic temperature dependence, with the sign of the Seebeck coefficient changing from negative to positive with decreasing temperature. The observed behavior is size-dependent and is attributed to limitations of the mean free path of the charge carriers within the nanowires. The observed size-dependent Seebeck coefficient and in particular the size-dependent sign change opens a promising avenue for single-material thermocouples with p- and n-legs made from nanowires with different diameters.

Influence of indium and selenium co-doping on structural and thermoelectric properties of Bi2Te3 alloys

The melt-grown, indium and selenium co-doped Bi2Te3 single-crystal system is studied with a purpose to improve and analyze the thermoelectric performance in the low and near room-temperature range (10–400 K). The influence of co-dopants on the crystalline perfection, symmetry, dislocation, and single-crystal quality is investigated using high-resolution X-ray diffraction. The surface morphological features show the existence of small-angle grain boundaries, white patches, and tilt boundaries. Degenerate type of semiconducting behavior is seen in all the samples over the entire temperature range. The existence of small polarons is experimentally inferred from temperature-dependent electrical resistivity. Measurement of Seebeck coefficient confirms p- to n-type transition in the crystals doped with indium and selenium. The total thermal conductivity at 11 K was decreased by 3.4 times in (Bi0.98In0.02)2Te2.7Se0.3 as compared to pristine sample. Therefore, this novel co-doped indium and selenium Bi2Te3 single-crystal combination is viable to use as a competitor for low and near-room-temperature thermoelectric applications.