Papers by Keyword: Thermoelectric Property

Abstract: Novel poly (selenophene-co-3-methylthiophene) was successfully achieved by directly electrochemical oxidation of the monomer mixtures of selenophene and 3-methylthiophene (3MeT) in boron trifluoride diethyl etherate. The effect of monomer concentration ratios on the copolymerization were investigated by cyclic voltammetry. The structures of as-prepared copolymers were characterized by UV-vis and infrared spectroscopy. The conductivity and thermoelectric measurements revealed the incorporation of 3MeT into the polyselenophene (PSe) chain improved significantly the conductivity and thermoelectric property of PSe.

Abstract: The reaction behavior of CuAlO₂ during the annealing at high temperatures was investigated. The relationship between thermoelectric properties including electrical resistivity, excess oxygen doping and decomposition of CuAlO₂ was discussed. The evolution of CuAlO₂ compact during the annealing mainly included excess oxygen doping, decomposition of CuAlO₂ into CuAl₂O₄ and CuO and complete decomposition of CuAlO₂ as following pattern : CuAlO₂ → CuAlO_2+x → CuAlO₂+CuO+ CuAl₂O₄ → CuAl₂O₄+CuO. Electrical resistivity of the compacts was decreased with excess oxygen doping, but increased when CuO and CuAl₂O₄ were formed. Thermoelectric performance of the compacts was improved due to the excess oxygen doping.

Abstract: Analysis model of finite element method with a random distribution for thermoelectric composites was built. Thermoelectric properties including electrical resistivity, Seebeck coefficient and thermal conductivity of M/TiO_2–x (M = Cu, Ni, 304 stainless steel (304SS)) thermoelectric composites were investigated by the proposed model. Cu/TiO_2–x composite showed a large decrease in electrical resistivity while 304SS/TiO_2–x composite thermal conductivity was slightly increased. Calculated dimensionless figure-of-merit, ZT of Ni/TiO_2–x composite was higher than those of TiO_2–x and the other composites in a wide range of metal volume fractions because Ni has large absolute values of Seebeck coefficient, power factor and dimensionless figure-of-merit compared to the other two metals. It was found that power factor and dimensionless figure-of-merit of thermoelectric composites depended on the balance among electrical resistivity, thermal conductivity and Seebeck coefficient. The results revealed that it is important for M/TiO_2–x composites to choose suitable addition metal with high power factor and dimensionless figure-of-merit.

Abstract: Ca₃Co₄O₉ powders were synthesized by a solid-state reaction method. Porous Ca₃Co₄O₉ ceramics with parallel sheet shaped pores were prepared by a template sacrifice method using epispastic polystyrend (EPS) hollow spheres as the templates. During compaction of the green body, the EPS hollow spheres change into EPS discs due to the pressing force. After sintering, the pores in the Ca₃Co₄O₉ ceramics are sheet shaped, well distributed and parallel to the pressing surface of compaction. The value of ZT merit of the porous Ca₃Co₄O₉ sample obtained with 10 wt% EPS spheres is 0.0489. It was found that the ZT merit value can be improved by changing the density of sample to achieve a high ratio of electrical conductivity to thermal conductivity.

Abstract: The relations between electronic structure and thermoelectric property of misfit layered cobaltite of Ca3Co4O9 and La-doped series are studied from the calculation by density function and discrete variation method (DFT-DVM). The highest valence band (HVB) and the lowest conduction band (LCB) near Fermi level are only mainly from O 2p and Co 3d in Ca2CoO3 layer. Therefore, the semiconductor, or thermoelectric property of Ca3Co4O9 should be mainly from Ca2CoO3 layer, but have no direct relation to the CoO2 layer, which is consistent with that binary oxides hardly have thermoelectric property, but trinary oxide compounds have quite good thermoelectric property. With the amount of La-doped increase, the gap between HVB and LCB firstly decrease, then reaches the minimum, finally increase. The gap affects the thermoelectric property. Therefore, there is a best amount of Na-doped to improve thermoelectric property, which is consistent with the experiment.

Abstract: Hydrochloric acid doped polyaniline and camphor sulfonic acid doped polyaniline were prepared by oxidative chemical polymerization and grinding, respectively. The structures of polyaniline samples were measured by Fourier transform infared spectroscopy. The Seebeck coefficient and electrical conductivity of the composites were investigated as protonic acid content in the temperature range from room temperature to 380K. The highest electrical conductivity of the 1M hydrochloric acid doped polyaniline reaches 5.57×10²S/m at 320K, and the mass ratio of 1:1 camphor sulfonic acid doped polyaniline reaches 5.97×10²S/m at 380K. This work suggests that a new method improves the thermoelectric properties of conducting polymers.

Abstract: Bi₂Te₃ bulk materials were prepared by combining chemical bath method and hot pressing at 80 MPa and 375 °C for 1 h. The samples before and after hot pressing were examined by X-ray diffraction, and the fracture surface of the bulk materials was observed by field emission scanning electron microscopy (FESEM). The electrical transport properties of the bulk materials were measured from room temperature up to 250 °C under Ar. The results indicate that sulfur addition can prevent the oxidation of Bi₂Te₃ nanostructures; however, it is not good to the thermoelectric properties of Bi₂Te₃ under the present synthesis conditions.

Abstract: The relations between electronic structure, chemical bond and thermoelectric property of misfit layered cobaltite of Ca₃Co₄O₉ and 3d transitional metal (Ti, Cr, Mn, Fe and Cu) doped series are studied using density function and discrete variation method (DFT-DVM). Ca₃Co₄O₉ consists of two layers of CoO₂ and Ca₂CoO₃. The highest valence band (HVB) and the lowest conduction band (LCB) near Fermi level are only mainly from O 2p and Co 3d in Ca₂CoO₃ layer. Therefore, the semiconductor, or thermoelectric property of Ca₃Co₄O₉ should be mainly from Ca₂CoO₃ layer, but it seems to have no direct relation to the CoO₂ layer, which is consistent with that binary oxides hardly have thermoelectric property, but trinary oxide compounds have quite good thermoelectric property. The variation of electronic structure, chemical bond strength and thermoelectric property of doping series is discussed. The improvement of thermoelectric property of Cu-doped Ca₃Co₄O₉ is the most obvious.

Abstract: In the present study, the TiO₂-Ti compacts with Magneli phases Ti_nO_2n-1 were fabricated using the mixed powder of TiO₂ powder and addition Ti powder by spark plasma sintering (SPS). The composition and the crystal types of Magneli phases Ti_nO_2n-1 were examined. The results showed that various Magneli phases Ti_nO_2n-1 (single or multi Magneli phases) with the composition of Ti_1+yO_2-x were obtained. The Magneli phases Ti_nO_2n-1 were formed in the transformation from the mother phase rutile TiO₂ to TiO with increase in Ti addition fraction. In addition, the thermoelectric properties of the sintered compacts were also measured. The electrical resistivity of the sintered compacts decreased with increase in Ti addition fraction. The thermoelectric performance of the sintered compacts was improved by the formation of Magneli phases Ti_nO_2n-1 with the composition of Ti_1+yO_2-x.

Abstract: Ca₃Co₄O₉ and Ca_3-xSm_xCo₄O9 powders were prepared by sol-gel process. The Ca-Co-O thermoelectric material ceramics were prepared. The ceramics materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microstructure and thermoelectric properties of ceramics were researched. The results indicate that the crystal of Ca_3-xSm_xCo₄O₉ with Sm adding growth ideally, the material had high density and low pore rate. The Ca_3-xSm_xCo₄O₉ ceramics contain directional array plate-shaped grains with layered structure. The thermoelectric properties of Ca_3-xSm_xCo₄O ceramics were excellent. There were high Seebeck coefficient and high electrical conductivity for Ca_3-xSm_xCo₄O₉ ceramics. The power factor increased with temperature increasing.