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1.
G. Rogl A. Grytsiv E. Royanian P. Heinrich E. Bauer P. Rogl M. Zehetbauer S. Puchegger M. Reinecker W. Schranz 《Acta Materialia》2013,61(11):4066-4079
Using thermoelectricity to directly convert (waste) heat energy into useful electricity faces a number of challenges. Not only are optimised thermal and electrical transport properties required resulting in a high figure of merit ZT and a high thermal–electric conversion efficiency η over a wide temperature range, thermoelectric (TE) materials must have sufficient mechanical integrity to survive continuous heating–cooling cycles. Thermal expansion of the material as well as the mechanical properties play an important role, i.e. their values should be as similar as possible for p- and n-type alloys to avoid stresses when used in a TE device. In this paper multiple filled p- and n-type skutterudites (Ba,Sr,DD,Yb)y(Fe1–xNix)4Sb12 with a ZT > 1 and η ≈ 13% are presented, for the first time showing, in contrast to hitherto investigated skutterudites, nearly identical thermal expansion coefficients and elastic moduli. The ZT values of these skutterudites could be further enhanced by more than 20% after severe plastic deformation via high-pressure torsion. 相似文献
2.
Norbert Mattern Ulla Vainio Jin Man Park Jun Hee Han Ahmed Shariq Do Hyang Kim Jürgen Eckert 《Journal of Alloys and Compounds》2011
The influence of Gd addition on phase separation of rapidly quenched Cu46Zr47?xAl7Gdx metallic glasses (x = 2,5,7) was studied. For low Gd content (x = 2), a homogeneous glass is obtained for the as-quenched state. Annealing leads to cluster formation by nucleation and growth prior to crystallization. For the Gd contents x = 5 and 7, early stages of spinodal decomposition are observed in the as-quenched glasses. Further annealing increases the amplitude of the compositional fluctuations prior to crystallization. Atom probe tomography gives evidence of the presence of Gd-enriched clusters of 2–5 nm size for the Cu46Zr42Al7Gd5 glass. The structure formation as a function of the Gd content is essentially determined by the composition dependence of the miscibility gap of the metastable undercooled melt. Early stages of spinodal decomposition or almost homogeneous glassy states are obtained if the critical temperature of liquid–liquid phase separation is close or below to the glass transition temperature. 相似文献
3.
《Journal of Alloys and Compounds》2006,407(1-2):314-317
Polycrystalline samples of Na1.5Co2−xAgxO4 (x = 0, 0.1 and 0.2) were synthesized from powder precursors prepared by a polymerized complex (PC) method. The thermoelectric power (S) and electrical resistivity (ρ) of Na1.5Co2−xAgxO4 (x = 0, 0.1, 0.2) were measured simultaneously in a helium atmosphere, in the temperature range from room temperature to 973 K. The thermoelectric power and power factor of Na1.5Co1.8Ag0.2O4 are higher than that of Na1.5Co2O4 over a wide range of temperatures. 相似文献
4.
《Intermetallics》2007,15(9):1202-1207
The thermoelectric properties of Sb-doped Mg2Si (Mg2Si:Sb = 1:x(0.001 ≦ x ≦ 0.02)) fabricated by spark plasma sintering have been characterized by Hall effect measurements at 300 K and by measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) between 300 and 900 K. Sb-doped Mg2Si samples are n-type in the measured temperature range. The electron concentration of Sb-doped Mg2Si at 300 K ranges from 2.2 × 1019 for the Sb concentration, where x = 0.001, to 1.5 × 1020 cm−3 for x = 0.02. First-principles calculation revealed that Sb atoms are expected to be primarily located at the Si sites in Mg2Si. The electrical resistivity, Seebeck coefficient, and thermal conductivity are strongly affected by the Sb concentration. The sample x = 0.02 shows a maximum value of the figure of merit ZT, which is 0.56 at 862 K. 相似文献
5.
The thermoelectric properties of Ag-doped compounds (Zn1?xAgx)4Sb3 (x = 0, 0.0025, 0.005, 0.01) have been studied at the temperatures from 15 to 300 K. The results indicate that low-temperature (T < 300 K) thermal conductivity of the moderately doped (Zn1?xAgx)4Sb3 (x = 0.0025 and 0.005) reduced remarkably as compared with that of Zn4Sb3 due to enhanced impurity (dopant) scattering of phonons. Electrical resistivity and Seebeck coefficient were found to increase first and then decrease obviously with the increase in the Ag content, which could be ascribed to the change of carrier concentration presumably due to different Zn positions occupied by Ag upon increasing doping content. Moreover, the lightly doped compound (Zn0.995Ag0.005)4Sb3 exhibited the best thermoelectric performance due to the improvement in both its electrical resistivity and thermal conductivity, whose figure of merit (at 300 K), ZT, is about 1.3 times larger than that of β-Zn4Sb3 obtained in the present study. Present results suggest that proper Ag doping in Zn4Sb3 is a promising way of improving its thermoelectric properties. 相似文献
6.
Microstructure and thermoelectric properties of CoSb2.75Ge0.25−xTex prepared by rapid solidification
Xianli Su Han Li Yonggao Yan Guoyu Wang Hang Chi Xiaoyuan Zhou Xinfeng Tang Qingjie Zhang Ctirad Uher 《Acta Materialia》2012,60(8):3536-3544
Since the vibration modes of the pnicogen rings in CoSb3-based skutterudites fall within the range of frequencies of heat-carrying phonons, disruption of the rings by doping should have a strong influence on heat transport in this material. To test the premise, single-phase double-doped CoSb2.75Ge0.25?xTex (x = 0.125–0.20) compounds were synthesized by combining melt spinning with a spark plasma sintering method. Following the melt-spinning process, the side of the ribbons contacting the copper drum is featureless and reflects its amorphous nature while the free surface of the ribbons is composed of 30–80 nm grains. After spark plasma processing the average grain size of the bulk samples is about 200 nm. High-resolution transmission electron microscopy images show an in situ nanostructure consisting of circular, 15 nm diameter dots of Te- and Ge-enriched skutterudite phase embedded in the skutterudite matrix. Transport properties were measured from 2 to 800 K as a function of Te and Ge content on the pnicogen (Sb) rings and the results were correlated with the structural data. Double-doping on pnicogen rings with Ge and Te, and using melt-spinning processing, results in binary skutterudite compounds that possess an impressive figure of merit of ZT ~ 1.1 at 750 K. 相似文献
7.
R.C. Mallik R. Anbalagan G. Rogl E. Royanian P. Heinrich E. Bauer P. Rogl S. Suwas 《Acta Materialia》2013,61(18):6698-6711
Skutterudites Fe0.2Co3.8Sb12?xTex (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) were synthesized by induction melting at 1273 K, followed by annealing at 923 K for 144 h. X-ray powder diffraction and electron microprobe analysis confirmed the presence of the skutterudite phase as the main phase. The temperature-dependent transport properties were measured for all the samples from 300 to 818 K. A positive Seebeck coefficient (holes are majority carriers) was obtained in Fe0.2Co3.8Sb12 in the whole temperature range. Thermally excited carriers changed from n-type to p-type in Fe0.2Co3.8Sb11.9Te0.1 at 570 K, while in all the other samples, Fe0.2Co3.8Sb12?xTex (x = 0.2, 0.3, 0.4, 0.5, 0.6) exhibited negative Seebeck coefficients in the entire temperature range measured. Whereas for the alloys up to x = 0.2 (Fe0.2Co3.8Sb11.8Te0.2) the electrical resistivity decreased by charge compensation, it increased for x > 0.2 with an increase in Te content as a result of an increase in the electron concentration. The thermal conductivity decreased with Te substitution owing to carrier–phonon scattering and point defect scattering. The maximum dimensionless thermoelectric figure of merit, ZT = 1.04 at 818 K, was obtained with an optimized Te content for Fe0.2Co3.8Sb11.5Te0.5 and a carrier concentration of ~n = 3.0 × 1020 cm?3 at room temperature. Thermal expansion (α = 8.8 × 10?6 K?1), as measured for Fe0.2Co3.8Sb11.5Te0.5, compared well with that of undoped Co4Sb12. A further increase in the thermoelectric figure of merit up to ZT = 1.3 at 820 K was achieved for Fe0.2Co3.8Sb11.5Te0.5, applying severe plastic deformation in terms of a high-pressure torsion process. 相似文献
8.
Norihiko L. Okamoto Tatsuya Koyama Kyosuke Kishida Katsushi Tanaka Haruyuki Inui 《Acta Materialia》2009,57(17):5036-5045
Phase relationships of manganese-substituted ruthenium sesquisilicide alloys have been investigated by using X-ray powder diffraction and scanning and transmission electron microscopy. A series of chimney–ladder phases Ru1?xMnxSiy (0.14 ? x ? 0.97, 1.584 ? y ? 1.741) are formed over a wide compositional range between Ru2Si3 and Mn4Si7. The compositions of these chimney–ladder compounds deviate slightly from the composition line connecting Ru2Si3 and Mn4Si7, which corresponds to the ideal composition line satisfying VEC (valence electron counting) = 14 rule. The occurrence of this compositional deviation is discussed in terms of the VEC rule and the atomic packing. The thermoelectric properties of the directionally solidified Ru1?xMnxSiy alloys (0.55 ? x ? 0.90) have also been investigated as a function of the Mn content and temperature. The dimensionless figure of merit (ZT) for those alloys with a high Mn content (x ? 0.75) increased with the increase in Mn content. The ZT value for a crystal with x = 0.90 was as high as 0.76 at 874 K. 相似文献
9.
Gangjian Tan Wei Liu Hang Chi Xianli Su Shanyu Wang Yonggao Yan Xinfeng Tang Winnie Wong-Ng Ctirad Uher 《Acta Materialia》2013,61(20):7693-7704
FeSb2Te, a ternary derivative of binary CoSb3, displays anomalous electrical and thermal transport properties because of considerable modifications in the band structure induced by Fe and significant mixed valence state (namely Fe2+ and Fe3+) scattering of phonons. The substitution of Te for Sb generates more holes without notably affecting the band structure, while markedly improving the electrical conductivity and retaining a high Seebeck coefficient due to the enhanced density of states, thereby leading to dramatically increased power factors. Furthermore, the heat carrying phonons are strongly scattered with increasing x value because of the formation of solid solutions between two end members: □FeSb2Te and □FeSb3 (where □ can be viewed as a vacancy). Consequently, high thermoelectric figures of merit were achieved in the FeSb2+xTe1?x compounds, with the largest ZT value reaching ~0.65 for the sample with x = 0.2. This is the highest value among all p-type unfilled skutterudites and is comparable with some filled compositions. Prospects for further improving the performance of p-type FeSb2Te-based skutterudites are discussed. 相似文献
10.
《Acta Materialia》2007,55(4):1441-1446
Ti1−xAlxN films have been shown to exhibit superior mechanical and thermal properties and are thus widely used for industrial applications. We have recently reported, that metastable NaCl-structure (c) Ti1−xAlxN decomposes to form c-TiN and c-AlN domains, and that the chemical requirement for spinodal decomposition is fulfilled over a broad composition and temperature range. Ab initio calculations showed that the maximum metastable solubility limit of AlN in c-TiN is in the range of 0.64–0.74, depending on the configurational entropy. The enthalpy change for decomposition of supersaturated c-Ti1−xAlxN into c-TiN and c-AlN has a maximum of ∼0.146 eV/at (28.18 kJ/mol) at x ∼ 0.61. Here, we use continuum mechanical investigations in addition to ab initio calculations to consider also the previously not described contribution of strain and surface energy on the energetic balance for this decomposition process. Based on these results a simple kinetic model for the decomposition process of c-Ti1−xAlxN can be developed. 相似文献
11.
Pb-alloyed AgSbTe2 (PbxAg20Sb30?xTe50 (x = 3, 4, 5 and 6)) composites were synthesized using a modified Bridgman method with a graphite mold to form plate-like samples. The Bridgman-grown specimens were dense, with few solidification cavities, and were sufficiently mechanically robust for a variety of electronic/thermal transport measurements. Inhomogeneity was found on the grain boundary, and was embedded with the nanoprecipitates of δ-Sb2Te with a feature size of 100 nm of the 5 at.% Pb and 6 at.% Pb specimens. A combined effect of alloying, inhomogeneity and nanoprecipitates leads to a low thermal conductivity of 0.3–0.4 W m?1 K?1, which approaches the theoretical minimum thermal conductivity of the amorphous material (κmin ~ 0.36 W m?1 K?1). A peak of the zT value, ranging from 0.7 to 0.8, is achieved at 425 K. Further annealing at 673 K increases the grain size and causes a reduction in the value of the zT peak to 0.4. 相似文献
12.
Single-phase polycrystalline dual-element-filled skutterudites BaxCeyCo4Sb12 (0 < x < 0.4, 0 < y < 0.1) are synthesized by the melting–quenching–annealing and spark plasma sintering methods. The electrical conductivity, Seebeck coefficient, thermal conductivity and low-temperature Hall data of these compounds are reported. Our results suggest that there is essentially no difference in electrical transport properties between the dual-element-filled BaxCeyCo4Sb12 and single-element-filled BayCo4Sb12 systems. The Ba–Ce co-filling is more effective in lattice thermal conductivity reduction than Ba single filling in the temperature range of 300–850 K. Very low lattice thermal conductivity values less than 2.0 W m?1 K?1 are obtained at room temperature. Consequently, enhanced thermoelectric figure of merits (ZT) for these dual-element-filled CoSb3 skutterudites are achieved at elevated temperatures, in particular ZT = 1.26 at 850 K for Ba0.18Ce0.05Co4Sb12.02. 相似文献
13.
The objective of this study is to investigate the formation of Ti3SiC2 from Ti/Si/C powders using the arc melting method. The results show that the sample sintered at 80 s produced a near single-phase of Ti3SiC2 (99.2 wt.%) with a relative density of 88.9%. These results were confirmed by phase determination using XRD analysis and were supported with micrographs from FESEM/EDX analyses. The relative density and porosity of all samples were dependent on the formation of macropores in bulk samples and micropores in TiCx grains. The proposed reaction mechanisms for the synthesis of Ti3SiC2 by arc melting is that Ti3SiC2 might be formed from TiCx + Si, Ti5Si3Cx + C, and Ti5Si3Cx + TiCx at early arcing time (≤ 10 s), while TiCx + TiSi2 take place at 15 s to 80 s. After 80 s, decomposition of Ti3SiC2 into TiCx, TiSi2 and C was observed. 相似文献
14.
Cui Yu Tie-Jun Zhu Rui-Zhi Shi Yun Zhang Xin-Bing Zhao Jian He 《Acta Materialia》2009,57(9):2757-2764
Half-Heusler thermoelectric materials Hf1?xZrxNiSn1?ySby (x = 0, 0.25, 0.4, 0.5; y = 0.02, 0.04, 0.06) have been prepared by levitation melting followed by spark plasma sintering or hot pressing. X-ray diffraction analysis and scanning electron microscopy observation show that single-phased half-Heusler compounds without compositional segregations have been obtained by levitation melting in a time-efficient manner. A small amount of Sb doping can improve the electrical power factor but undesirably increases the thermal conductivity due to the increased carrier thermal conductivity. The isoelectronic substitution of Zr for Hf substantially decreased the lattice thermal conductivity. A state-of-the-art ZT value of 1.0 has been attained at 1000 K for the levitation-melted and spark-plasma-sintered Hf0.6Zr0.4NiSn0.98Sb0.02, which is one of the highest achieved ZT values for half-Heusler thermoelectric alloys. 相似文献
15.
Michihiro Ohta Shuhei Satoh Toshihiro Kuzuya Shinji Hirai Masaru Kunii Atsushi Yamamoto 《Acta Materialia》2012,60(20):7232-7240
Titanium disulfide (TiS2) powder was prepared by sulfurizing TiO2 powder with CS2 gas at 1073 K for 4 h. Because CS2 gas is a powerful sulfurizing agent for TiO2, CS2 sulfurization can be performed at a low temperature. The TiS2 powder thus prepared was first mixed with sulfur powder in a mass ratio of 1:0.04 and pressure sintered at 973 K for 1 h under a uniaxial pressure of 50 MPa in vacuum. The addition of a small amount of sulfur powder to the TiS2 powder prevents sulfur deficiency in the sintered compact, resulting in the formation of a near-stoichiometric Ti1.008S2 composition. X-ray diffraction patterns show that the crystalline ab-axis is preferentially oriented perpendicular to the pressing direction. The Seebeck coefficient, electrical resistivity and thermal conductivity of the oriented TiS2 sintered compacts with near-stoichiometric and sulfur-poor (titanium-rich) compositions were measured in the temperature range 300–723 K. The thermoelectric figure of merit ZT was enhanced by prevention of sulfur deficiency and formation of the oriented texture. The highest ZT of 0.34 was observed at 663 K in Ti1.008S2 for the direction perpendicular to the pressing axis. 相似文献
16.
A systematic study of optical absorption spectra of Mo6S9?xIx (x = 6) molecular wire dispersions in ethanol, fractionated into different bundle diameter populations shows that electronic transitions shift significantly as a function of bundle diameter. Two electronic transitions show significant shifts: the Mo–S charge transfer peak shifts from 1.8 to 1.5 eV and the next inter-band transition shifts from 2.7 to 2.4 eV with increasing bundle diameter d, in the range 5–100 nm. This empirical observation hugely simplifies characterization of Mo6S9?xIx wire dispersions according to diameter, opening the way to rapid advances in processing of these materials. We discuss the possible origin of the shift, dismissing quantum size effects, impurities and solvatochromism as well as stoichiometric variations between x = 6 and x = 4.5. 相似文献
17.
The elastic properties of xAg2O–(50 ? x) P2O5–50V2O5 glasses are investigated using ultrasonic pulse-echo measurements and their elastic properties have been characterized at room temperature. Results from the studies show that both longitudinal and transverse velocities decrease with increase of Ag2O concentration. The elastic constants C11, C44 and Young's modulus show decreasing trend while constant C12, bulk modulus and Poisson's ratio show an increasing trend as the fraction of Ag2O increases. Another notable observation is that the glass with 15 and 40 mol% of Ag2O concentrations exhibits the low velocities and low elastic moduli. This behavior of the elastic properties is related to the change in the structure of glasses as well as the interatomic bonding. 相似文献
18.
Nonstoichiometric ternary thermoelectric materials Ag2?ySbyTe1+y (y = 1.26, 1.29, 1.32, 1.35, and 1.38) were prepared by a direct melt-quench and hot press process. In situ composites of AgSbTe2 and Sb2Te3 were obtained over the entire composition range with a typical Widmanstätten pattern. Thermoelectric properties were measured from 300 K to 673 K, which changed systematically with Sb2Te3 ratio. The phase transition occurring at about 633 K, forming the single phased AgSbTe2, can significantly influence the electrical transport properties. Various crystallographic defects in different scales, such as atomic ordering, nanodomains, dislocations and stacking faults, have been observed by high-resolution transmission electron microscopy and their influences on lattice thermal conductivity have been discussed. Due to the extremely low thermal conductivity (about 0.6 W m?1 K?1) and large positive Seebeck coefficient of ~250 μV K?1 detected in Ag0.71Sb1.29Te2.29, the maximum dimensionless figure of merit ZT of 1.37 was obtained at 600 K. 相似文献
19.
Jing Fan Huili Liu Xiaoya Shi Shengqiang Bai Xun Shi Lidong Chen 《Acta Materialia》2013,61(11):4297-4304
P-type compounds Cu2GaxSn1 ? xSe3 (x = 0.025, 0.05, 0.075) with a diamond-like structure were consolidated using hot pressing sintering (HP) and spark plasma sintering (SPS) techniques. High-temperature thermoelectric properties as well as low-temperature Hall data are reported. Microstructural analysis shows that the distribution of Ga is homogeneous in the samples sintered by HP but inhomogeneous in the samples sintered by SPS, even with an electrically isolating and thermally conducting BN layer during the sintering. The Seebeck coefficients of the samples sintered by HP and SPS show similar dependence on the carrier concentration and are insensitive to the composition inhomogeneity. In contrast, the composition inhomogeneity results in lower carrier mobility and thus lower electrical conductivity in the samples sintered by SPS than those sintered by HP. Lattice thermal conductivity is further reduced through Ga doping; however, this effect is weakened by the inhomogeneous distribution of Ga. Due to their larger carrier mobility and lower lattice thermal conductivity, the samples sintered by HP exhibit 15–35% higher thermoelectric figure of merits (ZT) than those SPS samples with a high Ga doping level and without the coated BN layer, in which the composition homogeneity is worse. A ZT value of 0.43 is obtained for the HP Cu2Ga0.075Sn0.925Se3 sample at 700 K. 相似文献
20.
The influence of Mg value in the MoO3–Mg–C mixture on the molybdenum carbide formation and the mechanism of reactions during mechanochemical process were investigated. In keeping with this aim, magnesium and carbon contents of the mixture were changed according to the following reaction: 2MoO3 + (6 − x) Mg + (1 + x) C = (6 − x) MgO + Mo2C + x CO. The value of x varied from 0 to 6. Differential thermal analysis (DTA) results for sample with stoichiometric ratio (x = 0) revealed that in the early stage, carbon reduced the MoO3 to MoO2 and subsequently highly exothermic magnesiothermic MoO2 reduction occurred after magnesium melting. Also, it was indicated that the exothermic reaction temperature shifted to before magnesium melting in the 11 h-milled sample (x = 0) and all the exothermic reactions happened, simultaneously. According to the experimental findings, molybdenum carbide (Mo2C) was synthesized in the mixture powder with stoichiometric ratio (x = 0) after 12 h milling process and the type of reactions was mechanically induced self-sustaining reaction (MSR). However, at lower Mg content in the MoO3–Mg–C mixture (0 < x ≤ 2), the magnesiothermic reduction occurred in MSR mode and activated the carbothermal reaction. Further decrease in Mg value (2 < x ≤ 3) resulted in MSR mode magnesiothermic reaction and gradual carbothermal reduction. In samples with lower magnesium contents, partial molybdenum oxide reduction proceeded through a gradual mode magnesiothermic reaction. 相似文献