Papers by Keyword: Thermoelectric

Abstract: Polyaniline has attracted a lot of attention for thermoelectric (T.E) applications, however their drawback materials is that they possess low power factors than the state-of-the-art materials such as BiTe-based, BiSb-based, PbTe-based, etc. ^[1-4]. Currently, in order to enhance the T.E properties, hybrids between the polymer and other components such as carbon materials, other polymers, and even inorganic materials are being investigated. In this work, the effect of MoS₂ addition on the T.E properties of polyaniline was investigated. The MoS₂ nanoflowers were first synthesized via hydrothermal process at 200 °C for 24 hrs after which they were used for templated in situ polymerization of polyaniline. The scanning electron microscope (SEM) image showed that the MoS₂ nanoflowers were covered with the polyaniline during the polymerization process and this was confirmed from the X-ray diffraction (XRD) analysis which showed existence of both the polyaniline and MoS₂ in the synthesized material. The electrical conductivity of polyaniline was reported to be 10^-3 S cm^-1 and it was noticed that addition of minute amounts of MoS₂ into polyaniline resulted in an enhancement of the electrical conductivities of up to two orders of magnitude. Nanocomposite with 5 % MoS₂ (PMX-5) showed optimized power factor values ranging from 6.30 x 10^-2 - 1.12 x 10^-3 μW m^-1 K^-2 for the temperature range studied. This study therefore provides a facile approach for synthesis of polyaniline-molybdenum disulphide nanocomposites and the results obtained confirm that transition metal dichalcogenides (TMDs) have a potential for the enhancement of T.E properties of polyaniline.

Abstract: The objective of this article was to demonstrate the alternative method to produce the metal electrode on ceramic substrate. AA1100 aluminium alloy was thin-coated on alumina substrate by friction surfacing using a CNC milling machine. The properties of the coating layer were presented. After that, the coated ceramic substrate was connected to a thermoelectric material and used as thermoelectric electrode of the thermoelectric cell. Voltage, differential temperature and electrical current were measured. Power and efficiency of the thermoelectric cell were calculated. The maximum temperature at hot side of the thermoelectric cell was 171.48 °C. At this temperature, the voltage was 0.00027 mV and the power was 0.000655 W. Efficiency of the fabricated thermoelectric cell was 4.715 x 10^-7.

Abstract: The effects of Zn and Cu on the thermoelectric properties of ferrite thin films were studied in this paper. The Zn-Cu ferritethin film was fabricated using ink-jet printing method. A minimum of 50 print cycles was required to obtain continuous film with approximately 9 μm thick thin films. The thickness of Zn-Cu ferrite thin films was decreased with increasing sintering temperature from 200 oC (9.21 μm) to 400 oC (5.48 μm). The XRD traces of Zn_xCu_1-xFe₂O₄ exhibit as plane reflection for cubic spinel phase of Zn_xCu_1-xFe₂O₄ and there were no impurity peaks detected with increasing Zn content and sintering temperature. The electrical conductivity of Zn_xCu_1-xFe₂O₄ thin film decreased from 1.18x10^-3 S/cm (x=0.0) to 0.48x10^-3 S/cm (x=1.0) with increasing Zn content. Positive Seebeck values were observed for all the samples, which indicated the samples were p-type. The Seebeck coefficient of Zn_xCu_1-xFe₂O₄ thin film increased from 6.36 μV/K (x=0.0) to 17.46 μV/K (x=1.0) with increasing Zn content.

Abstract: Thermoelectric properties of SrTiO₃ doped with 8%Pm at Sr site were investigated using density functional theory and generalized gradient approximation. The transport properties were calculated based on BoltzTraP code at temperature range 300-1200K. In electronic properties study Fermi level were shifted to conduction band region due to high contribution 4f orbital in Pm. Present study thermoelectric figure of merit ZT result was 0.395 at 300K and 0.638 at 1200K. This shows a considerably good value of ZT for SrTiO₃ as n-type oxide. Compared to previous work, ZT were at the range of 0.21 - 0.37 for temperature of 300-1000K in Pr, La, Ta and Ho.

Abstract: This paper proposes a new vacuum sensor with CMOS Metal-N-Poly thermoelectric materials which works for both thermoelectric sensing and resistive heating. A new method of vacuum measurement with self-heating is proposed based on the dual phases of heating and sensing for the same element which is realized with CMOS thermoelectric sensor. Using the TSMC 0.35 μm CMOS-MEMS process, the proposed thermoelectric sensor is designed and fabricated with standard CMOS materials of the 4th metal and N-polysilicon to form 64 pairs of central-symmetrical thermocouples. There is an air convection-sensing area at the center of membrane and is filled with array of micro-through-holes to enhance the effect of heat convection. When the air molecules move through the array of hole, the heat exchange will take away the heat to cause a temperature drop of sensing area which gives a weak voltage between the cold and hot end of the thermocouples. The heating of thermopile itself is designed at the first phase and sensing the output voltage at the second phase subsequently. According to a careful investigation of the measurement with a wide range of 10m~10k torr, our proposed sensing scheme based on a thermoelectric type sensor is proved for practical vacuum detection and most of all it is proved as a new approach to use a commercial thermopile without heater, which is easier to include than a special custom design.

Abstract: The Bi–Te thermoelectric system shows an excellent figure of merit (ZT) near room temperature. Research on increasing the ZT value for n‑type Bi–Te is imperative because the thermoelectric properties of this compound are inferior to those of the p-type material. For this purpose, n-type Bi₂Te_3-ySe_y powders with various amounts of Se dopant (0.3 ≤ y ≤ 0.6) were synthesized by a vacuum melting-grinding process to improve the physical properties. The ZT value of the sintered bodies was investigated in the temperature range of 298–423 K with regard to the electrical and thermal characteristics. As the Se content increased, the electrical conductivity decreased owing to a reduction in the carrier concentration, which improved the overall value of ZT. The thermal conductivity clearly decreased as the Se content increased in the temperature range of 298–373 K due to increased alloy scattering, as well as a reduction in the lattice thermal conductivity caused by crystal grain boundary scattering. At room temperature, Bi₂Te_2.7Se_0.3 (y = 0.3) exhibited the highest ZT of 0.85. At increased temperatures, the ZT value was highest for Bi₂Te_2.55Se_0.45 (y = 0.45), indicating that the optimal effect of the Se dopants varies depending on the temperature range.

Abstract: Electrical conductivity plays an important role in the performance of thermoelectric semiconductor material. This study discusses the electrical conductivity measurements of Zinc Oxide (ZnO) doping Aluminium (Al) pellet as a material of thermoelectric using four-point probe method at high temperatures. Al-doped ZnO (2 wt%) pellet was sintered at the temperature of 1100°C, 1200°C, 1300°C, 1400°C, and 1500°C with the heating rate of 8°C/minute. SEM and XRD tests show that the higher sintering temperature effects to larger grain sizes, better crystallinity, and lower porosity. There is no electrical conductivity in the sintering sample at 1100°C due to the small grain sizes and high porosity. In the sintering sample at 1500°C, the phase of ZnAl₂O₄ erupted. The highest electrical conductivity of 5923.48S/m of Al-doped ZnO pellet was obtained at the sintering temperature of 1400°C with measurement temperature of 500°C.

Abstract: Polycrystalline Bi_1-xCuSeO (0 ≤ x ≤ 0.05) ceramics were prepared by self-propagating high-temperature synthesis followed by spark plasma sintering method. All the samples correspond with single BiCuSeO phase and high vacancies sample had higher density. The highest power factor of 4.71×10^-4 W.m^-1.K^-2 was obtained by 5% Bi vacancies at 873K, which is about 32% higher than that of the pristine sample. Along with slight reduction of thermal conductivity, the maximum ZT reached 0.68. The results show that vacancy engineering is a promising method for thermoelectric applications of BiCuSeO and related ceramics.

Abstract: We report on preparation of Mg₂(Si,Ge,Sn)-based thermoelectric materials by a direct induction melting method in Al₂O₃ crucible. A 40 g ingot of Mg₂Si_0.8Sn_0.1Ge_0.1 was prepared after addition to the batch 10 wt% of Mg excess. Evolution of crystal structure of the induction melted sample upon annealing and spark plasma sintering (SPS) was tracked by room-temperature X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. An evidence for the formation of Mg₂(Si,Ge,Sn) solid solution was obtained from the crystal lattice parameter of this phase which was found to be larger than that of undoped Mg₂Si. XRD and SEM indicated that alongside with the main phase of the Mg₂(Si,Ge,Sn) solid solution, an impurity phase of Mg₂Sn exists in the sample. Amount of the Mg₂Sn impurity phase is significantly reduced in spark plasma sintered sample.

Abstract: We present the thermoelectric properties of individual PbTe (lead telluride) nanowire (NW) grown by a stress induced method. Temperature-dependent thermoelectric power and electrical conductivity in PbTe NW with diameter 125 nm were investigated in temperature ranging of 300−400 K. The PbTe NW was found to have a Seebeck coeficient S and electrical conductivity σ of −121 μV K⁻¹ and 138 S cm⁻¹ at 300 K, respectively. The calculated power factor (PF) of PbTe NW (d = 125 nm) demonstrate an enhancement, wich is higher than that have been previously reported in PbTe NWs. Such an enhanced thermoelectric performance can in part be attributed to the size effect of nanowires.