Papers by Keyword: CoSb3

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Authors: H. Cheng, H.H. Hng, Jan Ma
Abstract: Thermoelectric (TE) materials are attracting renewed attention for clean energy conversion. Reducing the dimension of materials to 2D/1D (e.g. thin film and nanowire) is one major approach to achieve high figure of merit (ZT) in the existing TE materials system. Electrodeposition has been widely used in fabricating various low dimensional TE materials. However, electrodeposition behavior of CoSb3 skutterudites is rarely reported. In this work, we report the co-deposition behavior of cobalt and antimony in citric based solutions by electrodeposition. The effects of deposition potential and concentration of cobalt and antimony containing precursors were studied. The focus of the study will be on the crystalline properties and chemical composition of the deposited films.
Authors: Soon Chul Ur, Joon Chul Kwon, Il Ho Kim
Abstract: Fe doped skutterudite CoSb3 with a nominal composition of FexCo1-xSb12 (0≤x≤2.5) have been synthesized by mechanical alloying (MA) of elemental powders, followed by vacuum hot pressing. Phase transformations during mechanical alloying and vacuum hot pressing were systematically investigated using XRD. Single phase skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. However, second phase in the form of marcasite structure FeSb2 was found to exist in case of x≥2, suggesting the solubility limit of Fe with Co in this system. Thermoelectric properties as functions of temperature and Fe contents were evaluated for the hot pressed specimens. Fe doping up to x=1.5 with Co in FexCo4-xSb12 appeared to increase thermoelectric figure of merit (ZT) and the maximum ZT was found to be 0.78 at 525K in this study.
Authors: Jae Yong Jung, Soon Chul Ur, Il Ho Kim
Abstract: The encapsulated induction melting was attempted to prepare the Sn-filled CoSb3 skutterudites and their electronic transport properties were investigated. Single phase δ-CoSb3 was successfully obtained by the subsequent isothermal heat treatment at 823K for 6 days in vacuum. The Sn-filled CoSb3 showed p-type conductivity at 300K to 700K at it is a highly degenerate semiconductor. Lattice contribution was dominant to thermal conductivity and it was considerably reduced by Sn filling in the CoSb3 skutterudite.
Authors: Tao Sui, Jing Feng Li, Song Zhe Jin
Abstract: The fabrication of electrodes is one of the key techniques in constructing thermoelectric elements for the practical applications. In this work, the commercial active brazing alloy “Incusil-ABA” was used for the joining of CoSb3 to the Cu surface of the graded electrode materials (Cu/AlN/Cu) by using spark plasma sintering (SPS). The bonding was performed in vacuum at temperatures 500°C for 10min. The brazing and diffusion bonding process were investigated by analyzing the crystal structure and microstructure of the bonding interface using X-ray diffraction and scanning electron microscopy, and its composition distribution was also analyzed by energy dispersive X-ray.
Authors: Moon Kwan Choi, Soon Chul Ur, Joon Chul Kwon, K.W. Cho, Il Ho Kim, Young Geun Lee, Sung Lim Ryu
Abstract: In an effort to synthesize homogenized single phase d-CoSb3, this study considers the mechanical alloying (MA) of elemental Co and Sb powders using a nominal stoichiometric composition followed by hot pressing. Single phase, undoped CoSb3 skutterudites were successfully produced by vacuum hot pressing using MA powders without subsequent annealing. Phase transformations during mechanical alloying, powder annealing, and hot pressing were systematically investigated using XRD and SEM. Thermoelectric properties were measured and compared with the results of similar studies. Temperature dependences were also evaluated, and their correlations to phase transformation were examined.
Authors: Wei Shu Liu, Bo Ping Zhang, Jing Feng Li, Heng Wang
Abstract: Single-phase polycrystalline CoSb3 skutterudite was prepared through a new combination of mechanical alloying (MA) and spark plasma sintering (SPS). In order to investigate the influence of MA conditions on the microstructure and thermoelectric properties, MA synthesis were carried out under various conditions with different milling times. The powder sample MAed for 6h still consisted of metal Sb, and then transformed to CoSb3 with a little amount of metal Sb and CoSb2 phases after MA for 15h. Further prolonging the MA time resulted in the decomposition of CoSb3 to CoSb2 phase. The average grain size of the SPSed samples decreased from 650nm to 250nm as MA-time was prolonged from 6 to 24h. Lattice parameters estimated form XRD patterns increase with the increasing MA time. All samples SPSed at 600°C for holding 5 min show an n-type conduction. The electrical resistivity was 1030, 895, 410, 260 μm for the samples from the MA-derived powders with MA-time of 6, 15, 24 and 33h at room temperature, respectively, then reduced to 60 μm at 400°C for all samples. An optimum MA time is 24 h in which the sample shows the highest power factor 612μW/m*K2 at 150°C.
Authors: De Gang Zhao, Li Wang, Yan Hong Cai, Wan Jiang, Li Dong Chen
Abstract: In this study, we designed a suitable electrode material was designed, Cu-W alloy, which achieved a good thermal match with CoSb3 thermoelectric (TE) material. By means of spark plasma sintering (SPS), Cu-W alloy was introduced into CoSb3/Ti/Cu-W TE element successfully. Finite element analysis showed that the maximum thermal residual stress appeared at the cylindrical surface zone close to the CoSb3/electrode interface. SEM and EPMA results showed that an intermetallic compound (IMC) layer formed at the CoSb3/Ti interface and EDS analysis confirmed the IMC layer was TiSb phase. Shear tests showed that the shear strength of CoSb3/Ti/Cu70W30 joint was about 50Mpa. The potential profile of the interface area was measured by the four-probe method and the result showed no abrupt change in voltage was found around the interface. The high temperature reliability evaluation showed the joint had high thermal duration stability.
Authors: Il Ho Kim
Abstract: In0.25Co4-xNixSb12 skutterudites were synthesized by encapsulated induction melting and consolidated by hot pressing, and their thermoelectric properties were examined at temperatures from 323 to 823 K. A single δ-phase was obtained successfully by subsequent heat treatment at 823 K for 24 h. In0.25Co4-xNixSb12 was an n-type semiconductor at all temperatures examined, indicating that Ni atoms acted as electron donors by substituting for Co atoms. The thermal conductivity was reduced considerably by In filling and Ni doping due to an increase in phonon scattering and impurity scattering. The thermoelectric properties were improved due to the low thermal conductivity as a result of In filling and the optimum carrier concentration caused by Ni doping.
Authors: Il Ho Kim
Abstract: Sn-filled and Fe-doped CoSb3 skutterudites were synthesized by encapsulated induction melting. A single δ-phase was obtained by subsequent annealing, as confirmed by X-ray diffraction. The as-solidified ingot consisted of mixed phases of -CoSb, -CoSb2, δ-CoSb3 and elemental Sb. The phases could be transformed by annealing, and the phases of the as-solidified ingot annealed at 773 K for 24 h transformed to δ-CoSb3. The temperature dependence of the Seebeck coefficient, electrical resistivity and thermal conductivity were examined from 300 K to 700 K. The positive Seebeck coefficient confirmed p-type conduction. The electrical resistivity increased with increasing temperature, which showed that the SnzCo3FeSb12 skutterudite is highly degenerate. The thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. The thermoelectric figure of merit was enhanced by Sn filling and its optimum composition was considered to be Sn0.3Co3FeSb12.
Authors: Ke Gao Liu, Wei Ping Zhang, Lei Shi
Abstract: For investigating the effect of wet milling time on thermoelectric properties, bulk CoSb3 was prepared via wet milling and sintering. The phases of samples were analyzed by X-ray diffraction and their thermoelectric properties were tested by electric constant instrument and laser thermal constant instrument. Experimental results show that, the major phases of the samples sintered from the powders wet-milled 2 and 6 hours are CoSb3 while the samples sintered from powders wet-milled 12 and 20 hours have more impurity phases under the experimental conditions in this work. The electric resistivities of the samples sintered from the powders wet-milled 2 and 6 hours increase with rising temperature, which show the characteristic of typical semiconductor electricity and P-type conducting due to the positive Seebeck coefficients. However, the samples sintered from powders wet-milled 12 and 20 hours show N-type conducting due to their negative Seebeck coefficients. The ZT values of the samples sintered from the powders wet-milled 2 and 6 hours are relatively higher than other samples, which increases with the temperature rising at 100~400 °C, the highest value is 0.078.
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