Papers by Keyword: Thermoelectric Material

Abstract: The study of Hall effect of Kondo semiconductor CeFe₂Al₁₀ is reported as a candidate of thermoelectric material used at low temperatures. Single crystals of CeFe₂Al₁₀ with orthorhombic crystal structure were grown by Al self-flux method. An anisotropy of the Hall effect is clarified by measuring Hall resistance by changing the direction of electrical current, magnetic field, and voltage respect to all the three crystal axes of orthorhombic crystal structure. The Hall effect of CeFe₂Al₁₀ has a strong anisotropy against the direction of magnetic field but weak anisotropy against the directions of current and voltage. The value of carrier concentration indicates that CeFe₂Al₁₀ is matallic, which causes a low performance as a thermoelectric material. In order to improve the value of dimensionless figure of merit, the electrons should be doped to CeFe₂Al₁₀.

Abstract: In this article, the influence of structural and phase changes on the thermoelectric properties of PbTe doped with CdSe compounds of various molar concentrations were studied. The research showed that with a minimum value of the lattice parameter of the formed new phases in the PbTe matrix (at an impurity concentration of 0.5 mol%), the specific electrical conductivity and thermoEMF coefficient have a minimum value. A further increase in concentration leads to an increase in these parameters.

Abstract: In this work, p-type thermoelectric material was produced by hot extrusion of pre-synthesized in injection molding machine Bi_0.5Sb_1.5Te₃ solid solution. During the research radial distribution of the Seebeck coefficient was confirmed and described in material’s cross section using thermal measuring probe. Such nonuniformity of the Seebeck coefficient is correlated with the strain-stress state of extrudate specifically with the distribution of accumulated strain intensity, which was obtained by mathematical modeling of extrusion process using the software package DEFORM.

Abstract: Organic polymer composites are relatively simple to process and are therefore used in thermoelectric materials. The organic polymers are used as an adhesive agent between thermoelectric material grains. Thermoelectric effects of poly (vinyl alcohol) (PVA) composited with sodium cobalt oxide (Na_xCoO₂) were studied in this work. PVA is a low cost and an excellent biocompatibility polymer. High electrical conductivity, high Seebeck coefficient and low thermal conductivity are required in thermoelectric materials. As PVA is an insulating material, the PVA in between Na_xCoO₂ grain boundaries has an effect on the low electrical conductivity of Na_xCoO₂ composite. This results in a decrease in thermoelectric efficiency. However, PVA has been utilized to increase the Seebeck coefficient and also enhance thermoelectric efficiency. In order to improve the electrical conductivity of Na_xCoO₂ composite, PVA removal was produced by furnace heating at 500̊ C to eliminate PVA from Na_xCoO₂/PVA sample. The general thermoelectric parameters including the Seebeck coefficient, electrical conductivity and power factor of Na_xCoO₂/PVA and PVA removal sample were compared. X-ray diffraction patterns (XRD) and scanning electron microscope (SEM) images were used to identify the phase identification and morphology study, respectively. The results showed that the PVA removal sample had higher electrical conductivity than the Na_xCoO₂/PVA sample. However, Na_xCoO₂/PVA sample had higher thermoelectric performance than the PVA removal sample because the Na_xCoO₂/PVA sample showed higher Seebeck coefficient and power factor.

Abstract: In this study, nanometer WO₃ powder was uniformly dispersed into the Cu₂SnSe₃ powder by ball milling process, and the WO₃/Cu₂SnSe₃ thermoelectric composite was prepared by spark plasma sintering (SPS). The results showed that the nano-WO₃ particles were mainly distributed in the grain boundary of Cu₂SnSe₃ matrix, and the grain growth of Cu₂SnSe₃ was inhibited. The addition of nano-WO₃ could enhance the electrical conductivity of Cu₂SnSe₃, and while the Seebeck coefficient increased slightly for the 0.4% WO₃/Cu₂SnSe₃ composite. The thermal conductivity was not decreased until the content of WO₃ exceeded 1.6%. The highest thermoelectric figure of merit ZT of 0.177 was achieved at 700 K for 0.4% WO₃/Cu₂SnSe₃ composite. The enhancement of ZT value of WO₃/Cu₂SnSe₃ thermoelectric material was mainly attributed to the improvement of the electrical properties.

Abstract: In this paper ZnSb thin films were prepared by radio frequency magnetron sputteringfrom a stoichiometric Zn₄Sb₃ target followed by thermal annealing. The influence of sputteringconditions on microstructure, surface morphology, crystallinity and electrical transport propertieswere investigated. For the range of sputtering power of 50 W to 125 W and working pressure of 0.7Pa, it was found that the content of compound ZnSb phase in the films as well as film crystallinitycould be enhanced greatly by increasing the sputtering power, and this effect may be reinforced bydecreasing the working pressure to 0.2 Pa. At 0.7 Pa, A maximum value of 2.99 μW/cmK² of powerfactor measured at room temperature was obtained at 100 W. The sample prepared at the samepower and lower pressure of 0.2 Pa has a room temperature power factor of 5.46 μW/cmK² which isalmost doubled.

Abstract: In this study, we investigated a CuAl_0.9Fe_0.1O₂ compound prepared at two different sintering temperatures in order to find out the effect of sintering temperature on the compound's figure of merit of thermoelectric properties. The thermoelectric CuAl_0.9Fe_0.1O₂ compound was prepared from high purity grade Cu₂O, Al₂O₃ and Fe₂O₃ powders. The mixture of these powders were ground and then pressed with uniaxial pressure into pellets. The pellets obtained were sintered in the air at 1423 K and 1473 K. X-ray diffraction (XRD) patterns showed a single phase of CuAl_0.9Fe_0.1O₂ with rhombohedral structure, , along with a trace of CuO second phase. Moreover, the XRD peaks of the sample sintered at 1423 K indicated that more Fe³⁺ atoms replaced Al³⁺ atoms in this sample than they did in the sample sintered at 1473 K. The average grain size of the CuAl_0.9Fe_0.1O₂ compound prepared increased with increasing sintering temperature, whereas its mean pore size and porosity decreased with increasing sintering temperature. The dispersed small pores markedly decreased the thermal conductivity of the compound, while the Fe³⁺ substitution of Al³⁺ increased its electrical conductivity. The highest figure of merit (ZT) found was 0.021 at 973 K in the CuAl_0.9Fe_0.1O₂ sample sintered at 1423 K. Our findings show that this low-cost material with a reasonable figure of merit is a good candidate for thermoelectric applications at high-temperature.

Abstract: The shear property of the thermoelectric material Bi₂Te₃ is inextricably linked with its layer structure. By the molecular dynamics method, the mechanism of shearing deformation was studied in this paper. In the simulation, cubic single-crystal simulation cells with different layer directions inside were adopted, ensuring that the c axis of crystal lattice can be along, across and 45^o deviated from the shear stress. Compared with all the calculation models, the results show that when the shear stress increases, slip occurs along the Te1-Te1 adjacent layers which are connected by the weak van der Waals bonding, and ultimately leads to structural fracture. Furthermore, size effect and loading modes can also impact the behavior of shearing deformation, however, in very different ways. Future efforts should be focused on the influence of the creation and motion of defects during the deformation as well as temperature effect and strain rate effect.

Abstract: We report on the effect of Ni doping on the thermoelectric properties of p-type BiCuSeO oxyselenide, with layer structure composed of conductive (Cu₂Se₂)^2- layers alternately stacked with insulating (Bi₂O₂)²⁺ layers along c axis. After doping with Ni, enhanced electrical conductivity coupled with a moderate Seebeck coefficient leads to a power factor of ~231 μwm^-1K^-2 at 873 K. Coupled to low thermal conductivity, ZT at 873 K is increased from 0.35 for pristine BiCuSeO to 0.39 for Bi_0.95Ni_0.05CuSeO. However, the efficiency of Ni doping in the insulating (Bi₂O₂)²⁺ layer is low, and this doping only leads to a limited increase of the hole carriers concentration. Therefore Ni doped BiCuSeO has relatively low electrical conductivity which makes its thermoelectric figure of merit much lower than that of Ca, Sr, Ba and Pb doped BiCuSeO.

Abstract: Nanometer-sized (Sr_xCa_1-x)₃Co₄O₉ powders were prepared using the sol-gel process. Two Ca-Co-O ceramic thermoelectric materials were then prepared and characterized with X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The microstructure and thermoelectric properties of the ceramic materials were studied. The experimental results showed that the crystals of (Sr_xCa_1-x)₃CO₄ grew into materials with high density and low pore rate under optimal Sr-doped conditions. The (Sr_xCa_1-x)₃Co₄O₉ ceramic materials contain directional arrays with cube-shaped grains in a layered arrangement. The crystals were fully developed and the interface between layers was clear-cut. The thermoelectric properties of (Sr_xCa_1-x)₃Co₄O₉ ceramics were greatly improved, with high Seebeck coefficient and high electrical conductivity. The Seebeck Coefficient positively correlated with the rise of temperature.