Increase In Seebeck Coefficient Research Articles

Enhanced thermoelectric performance of MoSe2 under high pressure and high temperature by suppressing bipolar effect

The electrical transport property of layered MoSe2 has a strong response to high pressure by enhancing the inter-layer interaction. However, the narrowed bandgap under high pressure will cause the bipolar effect (i.e., the thermally excited minority carriers contribute to a Seebeck coefficient with the opposite sign to the majority carriers) at high temperatures to degrade the thermoelectric (TE) performance. Hence, suppressing the bipolar effect is important to optimize the TE performance of MoSe2 under high pressure and high temperature (HPHT). In this study, the degradation of TE performance caused by the bipolar effect under HPHT in MoSe2 is investigated. It is found that in MoSe2, the electrical conductivity was improved significantly by pressure; however, the bipolar effect led to a significantly degraded Seebeck coefficient at high temperatures. By injecting massive carriers beforehand, the bipolar effect was suppressed to make a dominant type of p-type charge carries, achieving an increased Seebeck coefficient with increasing temperature, resulting in an improved power factor from 29.3 μW m−1 K−2 in MoSe2 to 285.7 μW m−1 K−2 in Mo0.98Nb0.02Se2 at 5.5 GPa, 1110 K. Combined with the reduced thermal conductivity by point defect scattering on phonons, a maximum ZT value of 0.11 at 5.5 GPa, 1110 K. This work highlights the significance of suppressing the bipolar effect under HPHT for optimizing TE performance in such layered semiconductors.

Uniformity of Thermoelectric Properties of N-type Bi<sub>2</sub>Te<sub>3-y</sub>Se<sub>y</sub> Bulky Compacts

Because n-type Bi<sub>2</sub>Te<sub>3</sub>-based materials exhibit lower thermoelectric performance than p-type materials and because their thermoelectric properties are sensitively changed by the composition and carrier concentration, optimizing these aspects in n-type materials is necessary to improve the thermoelectric figure of merit (ZT). In this study, the thermoelectric performance of n-type Bi<sub>2</sub>Te<sub>3</sub>-based materials was improved by reducing thermal conductivity through the formation of a Bi<sub>2</sub>Te<sub>3</sub>-Bi<sub>2</sub>Se<sub>3</sub> solid solution, Bi<sub>2</sub>Te<sub>3-y</sub>Se<sub>y</sub> and optimizing the carrier concentration through doping. As the amount of Se increased in Bi<sub>2</sub>Te<sub>3-y</sub>Se<sub>y</sub>, the carrier concentration decreased, resulting in decreased electrical and thermal conductivities and increased Seebeck coefficients. As a result, Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub> exhibited ZT = 0.56 at 323 K, and Bi<sub>2</sub>Te<sub>2.4</sub>Se<sub>0.6</sub> exhibited ZT = 0.60 at 423 K. Among the Bi<sub>2</sub>Te<sub>3-y</sub>Se<sub>y</sub> solid solutions, the doping effect was investigated for Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub> and Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub>, which recorded excellent thermoelectric performance at low temperatures. When halogen element (I) was doped, the power factor improved owing to the increase in carrier concentration, and the thermal conductivity decreased. As a result, the ZT values were greatly enhanced to ZT = 0.90 at 423 K for Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>:I<sub>0.005</sub> and ZT = 1.13 at 423 K for Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub>:I<sub>0.0075</sub>. When the transition elements (Cu and Ag) were doped, the power factor was improved by the increase in Seebeck coefficient, and thereby Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>:Ag<sub>0.01</sub> and Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>:Ag<sub>0.01</sub> exhibited ZT = 0.76 and ZT = 0.75 at 323 K, respectively, and Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub>:Cu<sub>0.01</sub> exhibited ZT = 0.73 at 423 K. Conversely, doping with other transition elements (Ni and Zn), as well as group-III (Al and In) and group-IV (Ge and Sn) elements, resulted in power factors and thermal conductivities that were similar to or slightly less than those of undoped Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>, leading to minimal or no improvement in ZT. Next, n-type Bi<sub>2</sub>Te<sub>2.85</sub>Se<sub>0.15</sub>:I<sub>0.005</sub> and Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub>:I<sub>0.0075</sub>, which exhibited the best thermoelectric performances, were fabricated as bulky compacts, and the uniformity of their thermoelectric properties were evaluated.

Re-optimising the thermoelectric properties of BiTeSe by CuO doping: From zone-melting ingots to powder metallurgy bulks with a large size

The Bi2Te3-based thermoelectric crystal ingots produced by the zone-melting (ZM) are the most widely used commercially at present. However, the poor mechanical properties caused by the ZM are unfavorable to the production of miniature devices. The mechanical properties can be improved by the powder metallurgy (PM), but the PM results in performance degradation of n-type Bi2Te3-based alloys, which could be attributed to the disappearance of intrinsic anisotropy and the increased carrier concentration originated from the “donor-like” effect of grain boundary. In this paper, the Bi2Te2.7Se0.3 + 4 wt% Te (BTST) powder was from the ground ZM ingots, and the influence of CuO doping on the thermoelectric properties of hot-pressed BTST polycrystalline bulks with a large size was investigated. It can be found that the thermoelectric properties of BTST are improved remarkably by CuO doping due to the increased Seebeck coefficient and suppressed thermal conductivity, which is caused by the synthetic effects of optimised carrier concentration, increased effective mass, and enhanced phonon scattering by the Cu2Te/Bi2Te2.7Se0.3 hetero-interfaces. Finally, the dimensionless thermoelectric figure of merit (ZT) of the sample (CuO)0.1(Bi2Te2.7Se0.3 + 4 wt% Te) reaches 1.32 at 408 K, which is about 65 % higher than that of the pristine BTST, and its average ZTave value reaches 1.27 in the temperature range of 300–473 K. The large size bulks produced by this method are not only commercialized directly, but also avoid the problem of poor mechanical properties.

Grain boundary, electrical transport and thermoelectric properties of the ultra-high rGO amount of C12A7-rGO composites

The Ca12Al14O33 ceramic (C12A7) and reduced graphene oxide (rGO) composite which an ultra-high amount (i.e., 40, 50, 60, and 70 wt%) of rGO (ultra-high amount C12A7/rGO composite) were synthesized by a solid-state reaction process. After the hydraulic press, the heat treatment in the temperature range of 773 K under the argon environment had been performed with the composite pellets for 30 min. XRD results of the C12A7 and all the ultra-high amount C12A7/rGO composites indicated a pure phase of C12A7 ceramic. Raman spectra confirmed the existence of rGO content in all the ultra-high amount C12A7/rGO composites. Raman peaks also suggested reduction of the free O22− and O2− ions from the framework of the ultra-high amount C12A7/rGO composites. SEM image presented the homogeneous grain boundary interface after the heat treatment at 773 K of the C12A7 wrapped by the rGO sheet, the agglomerated rGO sheet, and the rough interface stack of rGO sheets. UV-VIS spectroscopy presented the absorption behavior, direct energy gap, and indirect energy gap modifications of the ultra-high amount C12A7/rGO composites. Electrical conductivity of the ultra-high amount C12A7/rGO composites illustrated larger than 108 times improvement with temperature independence. Range of −5 to −17 μV/K , temperature dependence, and increased with rGO content increasing Seebeck coefficient were reported. Thermal conductivity of the ultra-high amount C12A7/rGO composites was increased with the rGO content increasing. Both the Power factor (PF) and the figure of merit (ZT) of the ultra-high amount C12A7/rGO composites were temperature dependent and were increased with the rGO content increasing, within the range of 0.4 μW/m.K2 of PF and the range of 3x10−4 of ZT, respectively. These experimental results verified grain boundary, modified energy band, electrical transport properties and thermoelectric properties of C12A7/rGO composites loading with ultra-high content rGO

Synthesis, Characterization and Power Factor Estimation of SnSe Thin Film for Energy Harvesting Applications

In this work, a simple, cost-effective successive ionic layer adsorption and reaction (SILAR) deposition technique has been used to deposit a high-quality tin selenide (SnSe) thin film onto a glass substrate. Structural, morphologic, and thermoelectric properties have been characterized for the prepared thin film. X-ray diffraction (XRD) results of the SnSe thin film reveal an orthorhombic structure phase. The morphological properties of the prepared thin films have been studied using field emission scanning electron microscopy (FESEM). The stoichiometric composition of the deposited thin film and the elemental binding energies of the Sn and Se elements have been investigated with energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The Fourier transformation infrared (FTIR) spectrum of the SnSe thin film displays vibrational modes of chalcogenides bonds. These results suggest that the developed thin film is crystalline, uniform, and without impurities and is appropriate for energy harvesting applications. The prepared thin film’s Seebeck coefficient and electrical resistivity were estimated through ZEM-3 from room temperature to 600 K. The power factor was evaluated. A substantially high electrical conductivity is observed, which decreases somewhat with temperature, suggesting a semimetal conducting transport—the absolute values of the Seebeck coefficient increase with temperature. The resulting power factor showed the highest values near room temperature and a somewhat decreasing trend as the temperature increased. Despite lower values of the Seebeck coefficient, the substantially enhanced power factor is due to the higher electrical conductivity of the thin film, superior to that reported previously. This precursor study demonstrates promising results for developing high-performance flexible thermoelectric devices via a simple and facile SILAR strategy.

Enhancing Strategy of the Small-Polaron Conductivity in LaCrO3: First-Principles Calculations and Experimental Validation.

LaCrO3 (LCO) has promising applications as a p-type conductive material in the fields of transparent conducting oxes, high-temperature sensors, and magnetohydrodynamic power generators. However, the easy volatility of the Cr element, along with the issues of low electrical conductivity caused by the small-polaron conduction mechanism and wide band gap, has hindered the widespread application of LCO. In this work, based on band engineering and defect engineering, we screened doping schemes through first-principles calculations that can reduce Cr volatility by enhancing the Cr-O bond energy. We also aimed to promote small-polaron hopping and improve the electrical conductivity by introducing impurity levels. Additionally, we conducted a thorough analysis of the small-polaron conductivity mechanism. Through the solid-state method, we successfully prepared codoped LCO with Ca and Zn. The Zn dopants effectively enhanced the Cr-O bond strength, suppressed the Cr volatility, and improved high-temperature stability. The Zn dopants introduced additional impurity energy levels within the band gap, significantly changing the mobility of small polarons. Through optimal doping concentration, the La0.7Ca0.3Cr0.95Zn0.05O3 sample demonstrated a significant enhancement in electrical conductivity compared to La0.7Ca0.3CrO3, increasing from 7 to 60 at 1000 K. Additionally, the impurity energy levels enhanced the asymmetry near the Fermi level, resulting in an increased Seebeck coefficient (S). This is beneficial for the production of high-temperature sensors. The output voltage of an LCO thermocouple module reaches up to 58 mV at 2170 K, indicating that the performance optimization strategy employed in this work has significant implications for the regulation and application of oxide electrical materials.

High thermoelectric performance of GeTe-MnTe alloy driven by spin degree of freedom

GeTe has been known as an excellent thermoelectrics, whereas its realistically application is limited by its structural phase transition near 700 K. Here, we show that the temperature of phase transition can be suppressed below 300 K by alloying 35% MnTe. The GeTe-MnTe alloy exhibits the much different transport properties from GeTe. Its room-temperature Seebeck coefficient is close to that of optimized GeTe, while its carrier concentration is one order higher. The increase of Seebeck coefficient of GeTe-MnTe is found to be accompanied with the decrease of magnetic susceptibility, while GeTe shows the opposite trend. By optimizing the carrier concentration with Bi doping and Bi/Sb co-doping, the peak figure of merit of GeTe-MnTe reaches 1.46 at 823 K. Our study reveals that GeTe-MnTe alloy is a novel and promising thermoelectric material.

Thermopower in Underpotential Deposition-Based Molecular Junctions.

Underpotential deposition (UPD) is an intriguing means for tailoring the interfacial electronic structure of an adsorbate at a substrate. Here we investigate the impact of UPD on thermoelectricity occurring in molecular tunnel junctions based on alkyl self-assembled monolayers (SAMs). We observed noticeable enhancements in the Seebeck coefficient of alkanoic acid and alkanethiol monolayers, by up to 2- and 4-fold, respectively, upon replacement of a conventional Au electrode with an analogous bimetallic electrode, Cu UPD on Au. Quantum transport calculations indicated that the increased Seebeck coefficients are due to the UPD-induced changes in the shape or position of transmission resonances corresponding to gateway orbitals, which depend on the choice of the anchor group. Our work unveils UPD as a potent means for altering the shape of the tunneling energy barrier at the molecule-electrode contact of alkyl SAM-based junctions and hence enhancing thermoelectric performance.

Electrically Programmed Doping Gradients Optimize the Thermoelectric Power Factor of a Conjugated Polymer

AbstractFunctionally graded materials (FGMs) are widely explored in the context of inorganic thermoelectrics, but not yet in organic thermoelectrics. Here, the impact of doping gradients on the thermoelectric properties of a chemically doped conjugated polymer is studied. The in‐plane drift of counterions in moderate electric fields is used to create lateral doping gradients in films composed of a polythiophene with oligoether side chains, doped with 2,3,5,6‐tetrafluoro‐tetracyanoquinodimethane (F4TCNQ). Raman microscopy reveals that a bias voltage of as little as 5 V across a 50 µm wide channel is sufficient to trigger counterion drift, resulting in doping gradients. The effective electrical conductivity of the graded channel decreases with bias voltage, while an overall increase in Seebeck coefficient is observed, yielding an up to eight‐fold enhancement in power factor. Kinetic Monte Carlo simulations of graded films explain the increase in power factor in terms of a roll‐off of the Seebeck coefficient at high electrical conductivities in combination with a mobility decay due to increased Coulomb scattering at high dopant concentrations. Therefore, the FGM concept is found to be a way to improve the thermoelectric performance of not yet optimally doped organic semiconductors, which may ease the screening of new materials as well as the fabrication of devices.

Enabling Oxidation Protection and Carrier-Type Switching for Bismuth Telluride Nanoribbons via in Situ Organic Molecule Coating.

Thermoelectric materials with high electrical conductivity and low thermal conductivity (e.g., Bi2Te3) can efficiently convert waste heat into electricity; however, in spite of favorable theoretical predictions, individual Bi2Te3 nanostructures tend to perform less efficiently than bulk Bi2Te3. We report a greater-than-order-of-magnitude enhancement in the thermoelectric properties of suspended Bi2Te3 nanoribbons, coated in situ to form a Bi2Te3/F4-TCNQ core-shell nanoribbon without oxidizing the core-shell interface. The shell serves as an oxidation barrier but also directly functions as a strong electron acceptor and p-type carrier donor, switching the majority carriers from a dominant n-type carrier concentration (∼1021 cm-3) to a dominant p-type carrier concentration (∼1020 cm-3). Compared to uncoated Bi2Te3 nanoribbons, our Bi2Te3/F4-TCNQ core-shell nanoribbon demonstrates an effective chemical potential dramatically shifted toward the valence band (by 300-640 meV), robustly increased Seebeck coefficient (∼6× at 250 K), and improved thermoelectric performance (10-20× at 250 K).

First-Principles Calculations of the Phonon, Elastic, and Thermoelectric Properties of a Ti2CO2 Monolayer.

The phonon, elastic, and thermoelectric properties of Ti2CO2 are investigated by first-principles calculations. The dynamic and mechanical stabilities of Ti2CO2 are confirmed. The Ti2CO2 monolayer exhibits strong acoustic-optical coupling with the lowest optical frequency of 122.83 cm-1. The TA mode originates from the contribution of Ti(XY) vibrations and has the largest gruneisen parameter at the Γ point; the LA mode has the main contribution of O(XY) and Ti(XY) vibrations and has the lowest gruneisen parameter at the M point. The analysis of the phonon spectrum indicates that the vibration contributions from C, O, and Ti atoms are mainly located in the low-, middle-, and high-energy regions, respectively. The Seebeck coefficient and electronic conductivity increase with increasing carrier concentration under room temperature. The analysis of mechanical properties shows that Ti2CO2 possesses a larger Young's modulus and bending modulus, which has a better ability to resist deformation. Thermal properties are further investigated.

Highly Conductive n‐Type Polymer Fibers from the Wet‐Spinning of n‐Doped PBDF and Their Application in Thermoelectric Textiles

AbstractThe field of electronic textiles currently lacks n‐type polymer fibers that can complement the more established p‐type polymer fibers. Here, a highly conductive n‐type polymer fiber is obtained via wet‐spinning of n‐doped poly(3,7‐dihydrobenzo[1,2‐b:4,5‐b’]difuran‐2,6‐dione) (n‐PBDF). The electrical conductivity of the fibers increases from 1000 to 1600 S cm−1 with increased draw during processing and correlates well with Young's modulus. Wide‐angle X‐ray scattering reveals the existence of a bimodal orientation of the polymer chains, favoring parallel alignment to the fiber axis with increased draw. After 14 d in 80% humid air, fiber conductivity stabilizes maintaining 81% of the initial conductivity. Although the electrical conductivity drops slightly over time, the Seebeck coefficient increases, resulting in the highest thermoelectric power factor being measured at 91 µW m−1 K−2 for the most drawn fiber 14 d after its fabrication. A proof‐of‐concept two‐couple thermoelectric textile is crafted by embroidering bundles of n‐type PBDF fibers and p‐type PEDOT:PSS fibers. The device generates 2.40 nW at a 22 °C temperature gradient. This work represents the initial steps and a crucial advancement toward fabricating high‐performance n‐type polymer fibers that can complement their p‐type counterparts to close the existing performance gap.

Discoveries on the link between the properties of thermoelectric and infrared radiation

Both thermoelectric conversion materials and infrared (IR) radiation materials enjoy broad applicability in energy utilization and aerospace. Therefore, it is essential to study the relationship between the physical properties of these two materials. This paper investigates the connection between the thermoelectric properties and the IR radiation properties using a SrTiO3-based thermoelectric material. As a result, we have demonstrated the correlation between a material's Seebeck coefficient and IR emissivity using experimental data and theoretical calculations. With increasing Seebeck coefficient, the IR emissivity increases. The material's IR emissivity falls as its electrical conductivity rises, and vice versa. When the material's thermal gradient is low, its IR emissivity influences its IR radiation energy. As the thermal gradient of the material increases, the IR radiation energy incident on the material surface is mainly influenced by the material's thermal conductivity. This work provides a fresh perspective on modulating the IR radiation and thermoelectric properties using the connection found in this study. The results provide theoretical guidance for studies at the intersection of thermoelectric and IR materials.

Complex microstructure induced high thermoelectric performances of p-type Bi–Sb–Te alloys

In this research, we have fabricated the complex microstructure features along with the high density of twin boundaries using the combination of magnetic pulse compaction (MPC) and spark plasma sintering (SPS), which are exclusively improved the thermoelectric transport properties of p-type Bi0.5Sb1.5Te3 alloys via effective scattering of carriers and phonons at the grain boundary interfaces. The texture analysis confirmed the formation of bimodal (mixed grains) microstructural features in MPC + SPS specimens sintered at 350 °C, and 400 °C respectively due to the adhesion of fine grains (grain growth) and initiation of recrystallization at high temperatures. In addition to high density of twin structure, high-angle grain boundaries have also been identified. The power factor of 3.53 mW/m.K2 was obtained for the MPC + SPS at 400 °C due to increased Seebeck coefficient and larger electrical conductivity values. The maximum reduced thermal conductivity of 1.14W/mK was recorded due to a significant reduction in lattice thermal conductivity, which is mainly owing to strong scattering of phonons at the formation of mixed grain microstructures with high-density dislocations. As a result, maximum figure of merit, ZT = 1.17was achieved for MPC + SPS at 400 °C temperature.

Realizing the thermoelectric performance in cobalt doped p-CuO semiconductor by valance band flattening and effective phonon scattering approach

In this work we investigated the thermoelectric properties of CuO microcrystals through band structure modification and effective scattering of charge carriers and phonons. Synergetic improvement in carrier concentration, band effective mass and magnetic moment of CuO through ferromagnetic cobalt doping has extensive impact for the simultaneous increase of electrical conductivity and Seebeck coefficient. Band conduction model was employed to study the conduction mechanism in detail. Modification in the electronic band structure through band flattening results average S2σ of 5.52 μW/mK2 in the temperature range of 300–873 K for an optimum doping level of 0.5 at% of Co, this is 3.5 times superior to undoped CuO. Moreover enormous phonon scattering centers such as point defects suppressed the lattice thermal conductivity from 4.43 W/mK to 1.92 W/mK at 873 K. These viable strategies aided to enhance the thermoelectric efficiency of our prepared samples to efficiently utilize non-exploited thermal energy into green energy production.

Effective decoupling of grain boundaries and secondary phase interfaces for enhanced thermoelectric performance of Cu1.8S/WS2 nanocomposites

Copper Sulfide (Cu1.8S) has influentially concerned the increasing attention in mid-temperature thermoelectric materials. The inherent low Seebeck coefficient and high thermal conductivity of Cu1.8S hinders the thermoelectric performance. The superionic conductivity exhibited by Cu1.8S phase possess characteristic phonon-liquid electron-crystal property eliminate transverse phonon vibrations. In this study, improved thermoelectric performance for the Cu1.8S material was obtained through the efficient strategy of compositing with WS2 nanoparticles. A minimum thermal conductivity of 1.4 W/mK at 753 K for the Cu1.8S/5 wt. % WS2 nanocomposite. Along with the increased Seebeck coefficient values, the thermal conductivity is suppressed by WS2 composite due to the formation of Cu2WS4 secondary phase which strengthens the phonon scattering. The evident reduction in the thermal conductivity, coupled with less affected Seebeck coefficient, led to increased figure of merit (zT) of 0.46 at 753 K, which is 95 % higher than that of pure Cu1.8S. This work provides a distinguished improvement in the performance of Cu1.8S thermoelectric material thereby enabling its employment in the application of waste heat harvesting.

Tuning the Radius Ratio to Enhance Thermoelectric Properties in the Zintl Compounds AM2Sb2 (A = Ba, Sr; M = Zn, Cd)

Five novel Zintl phase solid solutions in the Ba1–xSrxZn2–yCdySb2 (0 ≤ x ≤ 0.13(1); 0 ≤ y ≤ 0.32(2)) system were successfully synthesized by the molten Pb metal-flux method, and the powder X-ray diffraction and single-crystal X-ray diffraction analyses proved that all five title compounds adopted the BaCu2S2-type phase having the orthorhombic Pnma space group (Z = 4, Pearson code oP20) with five crystallographically independent atomic sites. The previously studied BaCu2S2-type antimonides demonstrated a limited tolerance for doping in contrast to the CaAl2Si2-type antimonides. To understand the relatively narrower phase width and limited dopability of the title BaCu2S2-type phase than the CaAl2Si2-type phase in the overall Ba1–xSrxZn2–yCdySb2 system, the radius ratio of cations and anionic elements r+/r– for two structure types were thoroughly investigated. For the first time, the r+/r– ratio was identified as a critical factor for the phase selectivity: (1) r+/r– > 1 favored the BaCu2S2-type phase, and (2) r+/r– < 1 favored the CaAl2Si2-type phase. We also revealed the structural transformation mechanism from the more widely observed CaAl2Si2-type phase to the title BaCu2S2-type phase as the relatively larger cationic elements were introduced to the system. A series of DFT calculations using the three hypothetical models indicated that a resonance peak near EF in the density of states curves was descended from the relatively flat band structure at several special symmetry points rationalizing the enhanced Seebeck coefficients of Ba0.94(1)Sr0.06Zn1.86(3)Cd0.14Sb2 and Ba0.96(1)Sr0.04Zn1.68(2)Cd0.32Sb2. Electron localization function analysis rationalized the correlation between the polarity change of anionic Zn/Cd–Sb bonds and the charge carrier mobility on the anionic frameworks. Temperature-dependent thermoelectric properties were studied for the four title compounds, and the results proved that the Sr and Cd doping in the title Ba1–xSrxZn2–yCdySb2 system successfully enhanced the ZT values through the increased Seebeck coefficients and the reduced total thermal conductivities.

Sputtering Codeposition and Metal-Induced Crystallization to Enhance the Power Factor of Nanocrystalline Silicon.

The power factor of highly boron-doped nanocrystalline Si thin films with controlled doping concentration is investigated. We achieve a high degree of tuning of boron content with a charge carrier concentration from 1018 to 1021/cm3 and with the electrical conductivity by varying the boron magnetron power from 10 to 60 W while maintaining the power of a SiB source constant during codeposition from two independent sputtering sources. Along with the increase in the electrical conductivity with increased boron doping, we observe a steady decrease in the Seebeck coefficient from 500 to 100 μV/K. These values result in power factors that exhibit a marked maximum of 5 mW/K2m for a carrier concentration of around 1021/cm3 at room temperature. Temperature-dependent measurements up to 650 °C show, with increasing doping concentration, a change of the resistivity from a semiconducting to a metallic behavior and an increase of both Seebeck coefficient and power factor, with this last one peaking at 9.8 mW/K2m in the 350-550 °C temperature range. For higher concentrations, scanning electron microscopy and energy-dispersive X-ray spectroscopy show a partial segregation of boron on particles on the surface. These results exemplify the great advantage of sputtering codeposition methods to easily tune and optimize the thermoelectric performance in thin films, obtaining in our specific case highly competitive power factors in a simple and reliable manner.

Effect of Zn atomic diffusion due to pulsed electric field treatment on the thermoelectric properties of Zn–Sb films

Zn4Sb3 has brought into sharp focus by its low cost and excellent thermoelectric (TE) properties in the medium temperature range. Zn atoms can diffuse in the Zn4Sb3 matrix under the treatment of temperature or current. This provides a way to control its TE performance. In this study, the TE properties of the Zn4Sb3 films were improved by the Zn atomic diffusion under the treatment of periodic pulsed electric field. The Zn atomic diffusion is caused by the electrostatic interaction of the pulsed electric field and the diffusion mode is related to the pulse period. When the pulse period is smaller than 10 s, the interstitial Zn atom diffuses first. The Zn vacancy increases, leading to the increase of the carrier concentration and the decrease of the resistivity. When the pulse period increases to 100 s, more Zn(1) atoms diffuse through the interstitial position, resulting in a small amount of ZnSb phase. Thereby in the Zn4Sb3 films, the carrier concentration decreases and the Seebeck coefficient increases. This kind of the synergistic effect decreases the resistivity and increases the Seebeck coefficient. The power factor of the Zn4Sb3 films treated with a pulse period of 100 s is more than 4500 μW m−1 K−2 in the range of 373 K–573 K. This study presents a new method to control atomic diffusion by periodic pulsed electric field, and the TE properties of the Zn4Sb3 films are improved.

Different concentrations of Ti4+ as a donor and electronic properties of Bi2-xTixO3

Bi(2-x)TixO3 (x = 0, 0.01, 0.03. &amp;amp; 0.05) (BO-xT) ceramics are prepared by conventional solid-state route followed by low sintering temperatures. X-ray diffraction analyses show the presence of the monoclinic phase of Bi2O3. The electrical conductivities at room temperature concerning the frequency (ranging from 25 kHz to 5 MHz) and Seebeck Coefficient ranging from 50°C to 400°C were measured. With an increase in Ti (dopant) content, the conductivity and Seebeck Coefficient increased with the temperature increment. The BO-0.03T has the highest Seebeck value (47 μV/°C), which shows a higher carrier concentration. In terms of electrical conductivities, the BO-0.05T ceramic shows the maximum electrical conductivity, i.e. 2.0 × 10−9 μS/m as compared to other samples, which exhibit the presence of free electrons. Moreover, relative permittivity (dielectric constant) and dielectric loss are also measured concerning the frequency at room temperature to investigate the dielectric behaviour of the ceramics. This low-temperature sintering ceramics will open new applications in the domain of electronic materials.