Showing papers on "Seebeck coefficient published in 2006"
TL;DR: In this article, the Czochralski method was used to grow a 46mm-long crystal of the Ba8Ga16Ge30 clathrate, which was cut into disks that were evaluated for thermoelectric performance.
Abstract: The Czochralski method was used to grow a 46-mm-long crystal of the Ba8Ga16Ge30 clathrate, which was cut into disks that were evaluated for thermoelectric performance. The Seebeck coefficient and electrical and thermal conductivities all showed evidence of a transition from extrinsic to intrinsic behavior in the range of 600–900K. The corresponding figure of merit (ZT) was found to be a record high of 1.35 at 900K and with an extrapolated maximum of 1.63 at 1100K. This makes the Ba8Ga16Ge30 clathrate an exceptionally strong candidate for medium and high-temperature thermoelectric applications.
401 citations
TL;DR: It is reported that the Ag-free system Na1 xPbmSbyTem+2, with appropriate combinations of m, y, and x, achieves record-high ZT values for a p-type bulk thermoelectric material, and shows that the high performance of these materials derives mainly from a low thermal conductivity.
Abstract: Thermoelectric materials are special types of semiconductors that function as “heat pumps” and as heat-to-electricity converters. Thermoelectric power generation allows for small size, high reliability, and quiet operation. Efficient thermoelectric-based heat-to-electricity converters require higher performance materials than are currently available. Direct conversion of heat to electricity could be achieved with solidstate devices based on thermoelectric materials. These devices could play an important role in future energy production, conversion, management, and utilization. When a temperature gradient is created across a thermoelectric module, a voltage is generated, owing to the Seebeck effect. This voltage can be used to drive an external load. Currently, there is a strong scientific and technological drive to identify new materials with enhanced thermoelectric figures of merit ZT= (sS/k)T (where s is the electrical conductivity, S the thermopower or Seebeck coefficient, k the thermal conductivity, and T the temperature). The numerator sS is called the power factor PF. Several classes of materials are currently under investigation, including complex chalcogenides, doped PbTe and its solid solutions, such as Pb1 xSnxTe, [5,6] superlattice thin films, and quantum-dot superlattices. Also of interest are skutterudites, metal oxides, and intermetallic clathrates. The superlattice thin-film structures of Bi2Te3/Sb2Te3 grown from chemical vapor deposition, and of PbSe0.98Te0.02/PbTe formed by molecular beam epitaxy (MBE) have figures of merit greater than ZT= 2 (at approximately 300 and 550 K, respectively). The MBE-grown thin films PbSe0.98Te0.02/PbTe are n-type materials and contain pyramid-shaped “nanodots” of PbSe of uniform size (approximately 20 nm), which form spontaneously inside a matrix of PbTe. Because energyconversion applications require materials in large quantities, we seek bulk analogues of these systems with similar figures of merit. A recent contribution to these efforts was the discovery of the n-type Ag-based tellurides AgSbTe2/PbTe, which can exhibit high figures of merit (ZT 1.7 at 700 K) when properly doped. To construct a fully functioning optimal thermoelectric device, both nand p-type materials are needed. To date, there is no p-type counterpart to AgSbTe2/ PbTe with similar performance. The highest figure of merit reported for p-type bulk materials (ZT 1.2 at 700 K) is exhibited by the so-called TAGS system (based on Te, Ag, Ge, and Sb: (GeTe)1 x((Ag2Te)1 y(Sb2Te3)y)x). [23] These Ge-containing materials, though more efficient than PbTe, have found limited use, owing to their high cost and to a lowtemperature phase transition. Recently, we described the ptype materials Ag(Pb1 ySny)mSbTe2+m, which show outstanding thermoelectric properties, reaching a maximum figure of merit of ZT 1.45 at 630 K. Herein, we report that the Ag-free system Na1 xPbmSbyTem+2, with appropriate combinations of m, y, and x, achieves record-high ZT values for a p-type bulk thermoelectric material. The effect of the composition on the thermoelectric properties is profound. We show that the high performance of these materials derives mainly from a low thermal conductivity. High-resolution transmission electron microscopy (HRTEM) demonstrates pervasive nanostructuring in Na1 xPbmSbyTem+2, which may be the root cause for the remarkably low thermal conductivity. The Na1 xPbmSbyTem+2 system was selected for study because it should be naturally prone to create Na,Sb-rich clusters in the lattice. The distribution of Na and Sb ions in the Pb sublattice cannot be random, as would be demanded by a solid solution, because Coulombic forces alone tend to drive the system to clustering at the nanoscale, thereby lowering the overall energy. The results described herein are in agreement with long-standing theoretical predictions that nanostructuring in semiconductors would lead to enhanced thermoelectric figures of merit. The Na1 xPbmSbyTem+2 materials could find applications in devices for power generation from a wide variety of hot sources, for example, vehicle exhausts, coal-burning installations, or electric power utilities. Na1 xPbmSbyTem+2 (y 1) samples (see Supporting Information for synthesis details) exhibit p-type conduction from 300 to 700 K. Ingots with the composition Na0.95Pb19SbTe21 (m= 19, x= 0.05, y= 1) exhibit an electrical conductivity of s= 1422 Scm 1 with a positive thermopower of S= 105 mVK 1 at room temperature. This leads to the relatively high power factor of PF= 15.6 mWcm K . The temperature dependence of the electrical conductivity and the thermopower of Na0.95Pb19SbTe21 are shown in Figure 1A. The conductivity decreases with increasing temperature, which is consistent with degenerate semiconductors, and reaches s= 150 Scm 1 at 700 K. However, the thermopower increases rapidly to S= 357.6 mVK 1 at 700 K, yielding a much higher power factor of PF= 19 mWcm K . For samples of composition Na0.95Pb20SbTe22 (m= 20, x= 0.05, y= 1), an electrical conductivity of s= 1541 Scm 1 and a [*] Dr. P. F. P. Poudeu, Prof. M. G. Kanatzidis Department of Chemistry Michigan State University East Lansing, MI 48824 (USA) Fax: (+1)517-353-1793 E-mail: kanatzid@cem.msu.edu
375 citations
TL;DR: In this paper, the authors explore electron filtering as a technique to increase the Seebeck coefficient and the thermoelectric power factor of heterostructured materials over that of the bulk.
Abstract: In this paper, we explore electron filtering as a technique to increase the Seebeck coefficient and the thermoelectric power factor of heterostructured materials over that of the bulk We present a theoretical model in which the Seebeck coefficient and the power factor can be increased in an ${\mathrm{In}}_{053}{\mathrm{Ga}}_{047}\mathrm{As}$-based composite material Experimental measurements of the cross-plane Seebeck coefficient are presented and confirm the importance of the electron filtering technique to decouple the electrical conductivity and Seebeck coefficient to increase the thermoelectric power factor
335 citations
TL;DR: In this article, the role of spin entropy contributions to thermopower was presented, in connection with strong electron correlation and triangular lattices, and it was found that good junctions can be formed using Ag paste including p- and n-type oxide powders.
Abstract: Layered CoO2 materials are excellent candidates for potential thermoelectric applications. Their single crystals show good p-type thermoelectric properties at temperatures higher than 800K in air.Recently, the mechanism of thermoelectric properties was clarified through a discussion of electronic and crystallographic structure. In order to fabricate thermoelectric modules possessing good power-generation properties, thermoelectric materials and metallic electrodes must be connected with low contact resistance and high mechanical strength.It has been found that good junctions can be formed using Ag paste including p- and n-type oxide powders.The role of spin entropy contributions to thermopower will be presented, in connection with strong electron correlation and triangular lattices.
327 citations
TL;DR: The conducting layered cobaltate NaxCoO2 exhibits several interesting electronic phases as the Na content x is varied, including water-induced superconductivity4 and an insulating state that is destroyed by field5.
Abstract: Research on the oxide perovskites has uncovered electronic properties that are strikingly enhanced compared with those in conventional metals. Examples are the high critical temperatures of the cuprate superconductors and the colossal magnetoresistance in the manganites. The conducting layered cobaltate Na(x)CoO2 exhibits several interesting electronic phases as the Na content x is varied, including water-induced superconductivity and an insulating state that is destroyed by field. Initial measurements showed that, in the as-grown composition, Na(x)CoO2 has moderately large thermopower S and conductivity sigma. However, the prospects for thermoelectric cooling applications faded when the figure of merit Z was found to be small at this composition (0.6 0.75, S undergoes an even steeper enhancement. At the critical doping x(p) approximately 0.85, Z (at 80 K) reaches values approximately 40 times larger than in the as-grown crystals. We discuss prospects for low-temperature thermoelectric applications.
257 citations
TL;DR: In this article, the authors discuss the potential for low-temperature thermoelectric cooling applications in the oxide perovskites, and discuss the possibility of low temperature applications.
Abstract: Research on the oxide perovskites has uncovered electronic properties that are strikingly enhanced compared with those in conventional metals. Examples are the high critical temperatures of the cuprate superconductors and the colossal magnetoresistance in the manganites. The conducting layered cobaltate $\rm Na_xCoO_2$ displays several interesting electronic phases as $x$ is varied including water-induced superconductivity and an insulating state that is destroyed by field. Initial measurements showed that, in the as-grown composition, $\rm Na_xCoO_2$ displays moderately large thermopower $S$ and conductivity $\sigma$. However, the prospects for thermoelectric cooling applications faded when the figure of merit $Z$ was found to be small at this composition (0.6$ $0.75, $S$ undergoes an even steeper enhancement. At the critical doping $x_p\sim$ 0.85, $Z$ (at 80 K) reaches values $\sim$40 times larger than in the as-grown crystals. We discuss prospects for low-temperature thermoelectric applications.
248 citations
TL;DR: In this paper, the authors investigated the thermoelectric properties of polycrystalline samples Ca1−xAxMnO3 (A=Yb, Tb, Nd, and Ho) and showed that the thermal conductivity is mainly driven by the atomic weight of the A site and decreases with it.
Abstract: CaMnO3 is an electron-doped compound which belongs to the perovskite family. Despite its high Seebeck coefficient S value, the figure of merit at high temperature remains low due to its large resistivity ρ(ρ300K=2Ωcm). To optimize the performance of this material in terms of thermoelectric properties, several substitutions have been attempted on the Ca site to decrease the ρ. Structure and thermoelectric properties of polycrystalline samples Ca1−xAxMnO3 (A=Yb, Tb, Nd, and Ho) have been investigated. Although ρ strongly depends on the ionic radius ⟨rA⟩ and carrier concentration, we have shown that the thermal conductivity κ is mainly driven by the atomic weight of the A site and decreases with it. Therefore, it seems that the S, ρ, and κ could be controlled separately. For instance, the highest dimensionless ZT (=0.16) has been obtained at 1000K in the air for Ca0.9Yb0.1MnO3.
222 citations
TL;DR: The efficiency of a thermoelectric material is determined by the dimensionless figure of merit as discussed by the authors, which is a function of the temperature difference between the hot and cold ends of the material.
Abstract: Thermoelectric materials convert a temperature difference into electricity and vice versa. [1–3] Such materials utilize the Seebeck effect for power generation and the Peltier effect for cooling. In the Seebeck effect, a temperature difference across a material causes the diffusion of charged carriers across that gradient, thus creating a voltage difference between the hot and cold ends of the material. Conversely, the Peltier effect explains the fact that when current flows through a material a temperature gradient arises because the charged carriers exchange thermal energy. Thermoelectrics perform these functions without moving parts or toxic gases, which make them unique among power generation and cooling methods. Presently, thermoelectrics find only limited use because of their poor efficiency. The efficiency of a thermoelectric material is determined by the dimensionless figure of merit
189 citations
TL;DR: In this article, thermoelectric bismuth telluride thin films were prepared on SiO2/Si substrates by radiofrequency (RF) magnetron sputtering.
164 citations
TL;DR: Ohta et al. as discussed by the authors compared the intrinsic thermoelectric properties of heavily Nb-doped TiO2 to those of heavy Nbdoped SrTiO3 at high temperatures (300-900K).
Abstract: To compare the intrinsic thermoelectric (TE) properties of heavily Nb-doped TiO2 to those of heavily Nb-doped SrTiO3 [S. Ohta et al., Appl. Phys. Lett. 87, 092108 (2005)], the electrical conductivity (σ), carrier concentration (ne), Hall mobility (μHall), and Seebeck coefficient (S) of heavily Nb-doped TiO2 (anatase) epitaxial films were measured at high temperatures (300–900K). The epitaxial films were grown on the (100)-face of LaAlO3 single-crystalline substrates by a pulsed-laser deposition technique at 800°C. The carrier effective mass (m*) of the anatase TiO2 epitaxial films was ∼1m0, which is an order of magnitude smaller than that of Nb-doped SrTiO3 (∼10m0). The estimated TE power factor (S2σ) of the ∼2%-Nb-doped anatase TiO2 film (ne∼5×1020cm−3) was ∼2.5×10−4Wm−1K−2 at 900K, which is approximately 15% of the 20%-Nb-doped SrTiO3 (1.5×10−3Wm−1K−2). The present findings will help establish a future TE material design concept for Ti-based metal oxides.
152 citations
TL;DR: In this paper, a polycrystalline K-filled CoSb3 was synthesized and the uplimit for K filling is at least 0.45, being higher than those of either alkaline earth (AE) or rare-earth (RE) metals but being in consistent with our earlier theoretical prediction.
Abstract: Polycrystalline K-filled CoSb3 are synthesized successfully. The uplimit for K filling is at least 0.45, being higher than those of either alkaline-earth (AE) or rare-earth (RE) metals but being in consistent with our earlier theoretical prediction. The measured transport properties (300–800K) show that K filling does not lower thermal conductivity much in comparison with AE or RE filling due to the relatively low mass of K atom. However, it improves electrical conductivity, retains large Seebeck coefficient, and leads to a reasonably good thermoelectric performance for the filled skutterudites. The maximum figure of merit ZT reaches 1 at 800K for K0.38Co4Sb12.
TL;DR: In this article, Bi2Te3 thin and superlattices were grown epitaxially by molecular beam epitaxy on BaF2 substrates with periods of 12 and 6nm, respectively.
Abstract: Multi-quantum-well structures of Bi2Te3 are predicted to have a high thermoelectric figure of merit ZT. Bi2Te3 thin films and Bi2Te3∕Bi2(Te0.88Se0.12)3 superlattices (SLs) were grown epitaxially by molecular beam epitaxy on BaF2 substrates with periods of 12 and 6nm, respectively. Reflection high-energy electron diffraction confirmed a layer-by-layer growth, x-ray diffraction yielded the lattice parameters and SL periods and proved epitaxial growth. The in-plane transport coefficients were measured and the thin films and SL had power factors between 28 and 35μW∕cmK2. The lattice thermal conductivity varied between 1.60W∕mK for Bi2Te3 thin films and 1.01W∕mK for a 10nm SL. The best figures of merit ZT were achieved for the SL; however, the values are slightly smaller than those in bulk materials. Thin films and superlattices were investigated in plan view and cross section by transmission electron microscopy. In the Bi2Te3 thin film and SL the dislocation density was found to be 2×1010cm−2. Bending of the ...
TL;DR: In this paper, the authors investigated thermoelectric properties of 20-nb-doped SrTiO 3 at high-temperature (300-1000 K) using single-crystalline epitaxial film, poly-crystaline film (average grain size ∼200 nm).
Abstract: We investigated thermoelectric properties of 20-%-Nb-doped SrTiO 3 at high-temperature (300-1000 K) using single-crystalline epitaxial film, polycrystalline film (average grain size ∼200 nm) and ceramic (average grain size ∼20 μm) samples to clarify the effect of grain boundaries on the thermoelectric performance. Although carrier concentration and Seebeck coefficient of all samples showed no significant differences, Hall mobility of the polycrystalline film was extremely small (<<10 -1 cm 2 V -1 s -1 at 300 K) as compared to those of the epitaxial film and the ceramic sample (∼3 cm 2 V -1 s -1 ). However, it drastically increased with increasing temperature and exhibited the value similar to those of the epitaxial film and the ceramic sample above 700 K. The thermoelectric figure of merit for 20%-Nb-doped SrTiO 3 was found to reach 0.35 at 1000 K irrespective of the grain size.
TL;DR: In this article, a combined process of mechanical alloying and spark plasma sintering was used to obtain a high power factor of 1766mW∕mK2 for the Ag08Pb22SbTe20 sample, which corresponds to a high dimensionless figure of merit.
Abstract: Polycrystalline AgnPbmSbTem+2n thermoelectric materials, whose compositions can be described as Ag08Pb18+xSbTe20 were prepared using a combined process of mechanical alloying and spark plasma sintering Electric properties of the sintered samples with different Pb contents were measured from room temperature to 700K The maximum power factor of 1766mW∕mK2 was obtained at 673K for the Ag08Pb22SbTe20 sample, which corresponds to a high dimensionless figure of merit, ZT=137 This best composition is different from that reported before
TL;DR: In this paper, a solgel dip coating technique with different percentages of Al on glass and silicon substrates was used to synthesize Al doped SnO2 thin films and X-ray diffraction studies confirmed the proper phase formation and atomic percentage of aluminium doping in the films was obtained by energy dispersive Xray studies.
Abstract: Al doped SnO2 thin films have been synthesized by a sol-gel dip coating technique with different percentages of Al on glass and silicon substrates. X-ray diffraction studies confirmed the proper phase formation in the films and atomic percentage of aluminium doping in the films was obtained by energy dispersive X-ray studies. SEM studies showed the particle sizes lying in the range 100–150 nm for the undoped films and it decreased with increase of Al doping. Optical transmittance spectra of the films showed high transparency (∼80%) in the visible region and the transparency increases with the increase of Al doping in the films. The direct allowed bandgap of the films have been measured for different Al concentration and they lie within the range of 3.87–4.21 eV. FTIR studies depicted the presence of Sn–O, Al–O, bonding within the films. The room temperature electrical conductivities of the films are obtained in the range of 0.21 S cm−1 to 1.36 S cm−1 for variation of Al doping in the films 2.31–18.56%. Room temperature Seebeck coefficients, SRT of the films were found in the range +56.0 μVK−1 to −23.3 μVK−1 for variation of Al doping in the films 18.56–8.16%. It is observed that the Seebeck coefficient changes its sign at 12.05% of Al in the films indicating that below 12.05% of Al doping, SnO2:Al behaves as an n-type material and above this percentage it is a p-type material.
TL;DR: In this article, the authors measured the thermoelectric properties of ZrNiSn-based alloy in the temperature range of 300-900K and showed that the performance can be improved by inducing appropriate nanoinclusions into the matrix.
Abstract: The Zr0.5Hf0.5Ni0.8Pd0.2Sn0.99Sb0.01∕ZrO2 nanocomposites have been prepared by spark plasma sintering technique. The thermoelectric properties were measured in the temperature range of 300–900K. Thermal conductivity for the nanocomposites is considerably reduced, because the nanophase scatters the thermal phonons which transport most of the heat in the ZrNiSn-based alloy. Seebeck coefficient for the nanocomposites is enhanced due to the potential barrier scattering. The dimensionless figure of merit ZT is improved, with ZT≈0.75 at 800K for the samples containing 9vol% ZrO2 nanoinclusions. The results obtained suggest that considerable improvements in the thermoelectric figure of merit may be obtainable by inducing appropriate nanoinclusions into the matrix.
TL;DR: In this article, the effects of SiC dispersion on the thermoelectric properties of the SPS-sintered Bi2Te3 alloys were investigated and it was shown that SiC nano-particles increased the absolute value of Seebeck coefficient.
Abstract: Nano-SiC dispersed Bi2Te3 was synthesized by mechanical alloying (MA) followed by spark plasma sintering (SPS). The effects of SiC dispersion on the thermoelectric properties of the SPS-sintered Bi2Te3 alloys were investigated. The results revealed that SiC dispersion in the Bi2Te3 matrix increased the absolute value of Seebeck coefficient. Although the electrical resistance was increased somewhat, Bi2Te3 with 0.1 wt% SiC showed a higher power factor than Bi2Te3 without SiC. Because the dispersion of SiC nano-particles reduced the thermal conductivity at the same time, 0.1 wt% (∼0.24 vol% SiC) addition of SiC nano-particles increased the figure of merit of Bi2Te3 by 18%. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, a series of copolymers consisting of both 2,5-dimethoxy-substituted phenylenevinylene units and unsubstitution units (P(MeOPV- co -PV)) were evaluated from the viewpoint of their thermoelectric properties.
TL;DR: In this article, the electrical resistivity, Seebeck coefficient, and thermal conductivity for a series of misfit-layered oxides Ca3Co4−xFexO9+δ (x=0, 0.05 and 0.15, respectively) were measured using powder x-ray diffraction data.
Abstract: The authors report measurements of the electrical resistivity, Seebeck coefficient, and thermal conductivity for a series of misfit-layered oxides Ca3Co4−xFexO9+δ (x=0, 0.05, 0.1, 0.15, 0.2) prepared by solid state reaction. Structural parameters are refined with superspace group of X2∕m(0b0)s0 using powder x-ray diffraction data. With partial substitution of Fe+2 for Co+3, the resistivity decreases, while the thermopower increases simultaneously. The x=0.05 sample exhibits a higher figure of merit (Z=3.01×10−4K−1) than that of Ca3Co4O9+δ (0.33×10−4K−1) at 300K, indicating much improvement of thermoelectric characteristics via partial substitution of Fe for Co.
TL;DR: In this article, the authors studied the properties of the thermoelectric material known as Zn 4 Sb 3, using X-ray diffraction techniques, resistance, and Seebeck coefficient measurements at various temperatures ranging from 4 to 773 K.
Abstract: Composition, crystal structures, polymorphic transformations, and stability of the thermoelectric material known in the literature as "Zn 4 Sb 3 " have been studied on a polycrystalline sample and Bi-flux-grown single crystals using X-ray diffraction techniques, resistance, and Seebeck coefficient measurements at various temperatures ranging from 4 to 773 K. Microprobe analysis yields the composition of the flux-grown crystals to be close to Zn 13 Sb 10 , with minor Bi doping. High-temperature X-ray and Seebeck coefficient studies show that the phase is unstable at high temperatures in a vacuum because of Zn losses. Both X-ray diffraction and resistivity measurements indicate the presence of two consecutive symmetry-breaking transitions below room temperature, in agreement with_our previous results on polycrystalline samples. Application of Landau theory suggests that the first R3c - C2/c symmetry breaking may be second-order in nature. The second, low-temperature symmetry breaking may proceed along two routes. One of these pathways, a first-order C2/c - Cl symmetry reduction, may lead to an incommensurate structure and is consistent with our experimental observations.
TL;DR: The role of these hybrid composite structures based on nanomaterials incorporated into the bulk matrix and the potential for enhanced performance is discussed in this paper, where the authors highlight the role of the hybrid composite structure based on carbon nanotubes and nanowires.
Abstract: Over a decade ago, Dresselhaus predicted that low-dimensional systems would one day serve as a route to enhanced thermoelectric performanceIn this article, recent results in the thermoelectric properties of nanowires and nanotubes are discussed Various synthesis techniques will be presented, including chemical vapor deposition for the growth of thermoelectric nanostructures in templated aluminaElectrical transport measurements of carbon nanostructures, such as resistivity and thermopower, have revealed some very interesting thermoelectric propertiesChallenges still remain concerning the measurement of individual nanostructures such as nanowiresMuch work has been performed on the thermoelectric properties of carbon nanotubes, and these results will be highlightedIn addition, routes for enhanced thermoelectric materials have focused on incorporating nanostructures within the bulk materialsThe role of these “hybrid composite structures” based on nanomaterials incorporated into the bulk matrix and the potential for enhanced performance are discussed
TL;DR: In this article, a small thermoelectric module composed of 140 pairs of oxide unicouples was used to charge a lithium-ion battery in a mobile phone, achieving 4.5V at a TH of 1072K in air.
Abstract: High power density is a strong point of thermoelectric generation. Exploitation of this salient characteristic would make thermoelectric modules promising candidates for mobile power applications. Here we show how power can be generated using a small thermoelectric module composed of 140 pairs of oxide thermoelectric unicouples. The module weighs 19.8g and its dimensions are 53mm long, 32mm wide, and 5.0mm thick. The hot-pressed thermoelectric oxide bulk materials used were connected with a Ag paste, incorporating oxide powder, and Ag electrodes. The module’s open circuit voltage increases with increasing hot-side temperature (TH) and reaches 4.5V at a TH of 1072K in air. No deterioration in output power was seen when power generation was carried out ten times at a TH of 723K with intermediate cooling to room temperature. The module was successfully used to charge a lithium-ion battery in a mobile phone.
TL;DR: In this paper, the thermoelectric properties of single-wall carbon nanotube (SWNT)/ceramic nanocomposites produced by spark-plasma-sintering have been investigated.
TL;DR: In this article, half-Heusler compounds of Sn-doped TiCoSb were prepared and their thermoelectric properties were measured above room temperature, and the maximum value of ZT for p-type material is 0.030 at 988 K in the sample of TiCoSn 0.05 Sb 0.95.
TL;DR: In this paper, the authors synthesized polycrystalline Sr2IrO4 and measured its magnetic susceptibility, electrical resistivity, specific heat, Seebeck coefficient, and thermal conductivity.
Abstract: We have synthesized polycrystalline Sr2IrO4 and measured its magnetic susceptibility, electrical resistivity, specific heat, Seebeck coefficient, and thermal conductivity. The magnetic susceptibility χ(T) shows a ferromagnetic transition at 250 K while the behaviour above the transition temperature is well described by a Curie–Weiss fit with a small effective moment μeff = 0.33 μB and a paramagnetic Curie–Weiss temperature, θCW = +251 K, consistent with previous studies on this compound. However, specific heat, Seebeck coefficient, and thermal conductivity are all dominated by the phonon contribution and show no anomalies at the ferromagnetic transition. Electrical resistivity, unlike the single crystal, shows a huge increase, three orders of magnitude, with decreasing temperature. The temperature dependence of resistivity is logarithmic at high temperatures (210 K
TL;DR: In this article, a preferentially orientated microstructure with the (1 1 0) plane parallel to and the basal planes (0 0 l) perpendicular to the pressing direction was formed, and the orientation factors of the (0 l) planes changed from 0.11 to 0.12 at different sintering temperatures.
Abstract: In the present work, starting from elemental bismuth, antimony and tellurium powders, p-type 25%Bi2Te3–75%Sb2Te3 thermoelectric materials with high density were prepared by mechanical alloying (MA) and plasma activated sintering (PAS). The single phase 25%Bi2Te3–75%Sb2Te3 alloys were obtained after MA for 12 h. The effect of sintering temperatures on microstructure and thermoelectric properties of the as-PASed samples was researched. Highly compact samples with relative density over 99% could be obtained when sintering temperature was over 653 K. A preferentially orientated microstructure with the (1 1 0) plane parallel to and the basal planes (0 0 l) perpendicular to the pressing direction was formed, and the orientation factors of the (0 0 l) planes changed from 0.11 to 0.12 at different sintering temperatures. The maximum power factor and figures of merit (Z) at room temperature were 3.10 × 10−3 W m−1 K−2 and 2.85 × 10−3 K−1, respectively. The Vickers microhardness reached 112.7 Hv, which was twice that of the single crystal samples prepared by zone-melting.
TL;DR: In this paper, it was shown that the Seebeck coefficient of misfit cobaltites is governed by the incommensurability ratio and/or the charge of the RS block.
Abstract: The ceramics of misfit cobaltites form a large family of layer oxides which exhibit large values of Seebeck coefficient (S 300K ≥ 90μV.K -1 ). They can be divided in two categories depending on the number of the rocksalt-type (RS) layers, n = 3 or n = 4, separating the [CoO 2 ] conducting layers. From the comparison of their structural features, it is found that the S values are governed by the incommensurability ratio and/or the charge of the RS block. This is clearly evidenced by making chemical substitutions at the level of the RS block: isovalent but with cations of different ionic radius (r Ba 2+ > r Sr 2+ > r Ca 2+ ) modifying the incommensurability ratio or aliovalent substitutions for cobalt (Pb 4+ , Ti 4+ ) which keep unchanged the structural incommensurability but make the RS charge changing.
TL;DR: DSC measurements and powder X-ray diffraction data indicate that this is a congruently melting phase at 1416 K and the negative Seebeck coefficient indicates transport processes dominated by electrons as carriers.
Abstract: A molten Al flux method was used to grow single crystals of the type I clathrate compound Ba8Al14Si31. Single-crystal neutron diffraction data for Ba8Al14Si31 were collected at room temperature using the SCD instrument at the Intense Pulsed Neutron Source, Argonne National Laboratory. Single-crystal neutron diffraction of Ba8Al14Si31 confirms that the Al partially occupies all of the framework sites (R1 = 0.0435, wR2 = 0.0687). Stoichiometry was determined by electron microprobe analysis, density measurements, and neutron diffraction analysis. Solid-state 27Al NMR provides additional evidence for site preferences within the framework. This phase is best described as a framework-deficient solid solution Ba8Al14Si31, with the general formula, Ba8AlxSi42-3/4x[]4-1/4x ([] indicates lattice defects). DSC measurements and powder X-ray diffraction data indicate that this is a congruently melting phase at 1416 K. Temperature-dependent resistivity reveals metallic behavior. The negative Seebeck coefficient indicat...
TL;DR: In this paper, the authors presented the temperature-entropy analysis, where the Thomson effect bridges the Joule heat and the Fourier heat across the thermoelectric elements of a cooling cycle to describe the principal energy flows and performance bottlenecks or dissipations.
TL;DR: In this article, the physical properties of an oxygen stoichiometric sample, YBaCo 4 O 7, have been studied by T -dependent measurements of the electrical resistivity ( ρ ), Seebeck coefficient (S ), and magnetization.