Adul Harnwunggmoung

Chalcopyrite CuGaTe2: A High‐Efficiency Bulk Thermoelectric Material

CuGaTe(2) with a chalcopyrite structure demonstrates promising thermoelectric properties. The maximum figure of merit ZT is 1.4 at 950 K. CuGaTe(2) and related chalcopyrites are a new class of high-efficiency bulk thermoelectric material for high-temperature applications.

High-temperature thermoelectric properties of thallium-filled skutterudites

The high temperature thermoelectric (TE) properties of polycrystalline Tl-filled skutterudites TlxCo4Sb12 (x=0, 0.05, 0.10, 0.15, 0.20, and 0.25) were examined from room temperature to 750 K. All samples exhibited negative Seebeck coefficients. The electrical resistivity, absolute values of the Seebeck coefficient, and the lattice thermal conductivity were found to decrease with increasing Tl content. Tl0.25Co4Sb12 exhibited the best TE performance; the maximum value for the dimensionless figure of merit ZT was 0.90 at 600 K.

Thermoelectric properties of Ga-added CoSb3 based skutterudites

Filled skutterudite compounds are known as excellent thermoelectric (TE) materials. It is known that the voids in the structure of the skutterudite compounds, such as CoSb3, can be filled or partially filled with a variety of different atoms, and, thus, obtained filled skutterudite compounds exhibit quite low thermal conductivity (κ). In the present study, we tried to fill Ga into the voids of CoSb3. The polycrystalline samples of GaxCo4Sb12 (x = 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) were prepared, and the TE properties were examined from room temperature to 750 K. All the samples were composed of two phases: GaxCo4Sb12 (x = ∼0.02) as the matrix phase and Ga metal as the second phase. All the samples exhibited negative values of the Seebeck coefficient (S). The Hall carrier concentration slightly increased with increasing x, while the carrier mobility decreased. Although the maximum Ga filling ratio was really low, the κ was reduced effectively by Ga adding. The maximum value of the dimensionless figure...

High-temperature thermoelectric properties of Cu2Ga4Te7 with defect zinc-blende structure

Here we show the high-temperature thermoelectric (TE) properties of Cu2Ga4Te7 with the defect zinc-blende structure in which one-seventh of the cation sites are structural vacancies. Cu2Ga4Te7 exhibited relatively low electrical resistivity (ρ) and thermal conductivity (κ) and moderate positive Seebeck coefficient (S) at high temperatures, making this compound a promising high-performance p-type TE material. At 940 K, the S, ρ, and κ were +215 μV K−1, 10.1×10−5 Ω m, and 0.67 Wm−1 K−1, respectively, which resulted in the maximum dimensionless figure of merit ZT (=S2T/ρ/κ, where T is the absolute temperature) of 0.64.

Enhancement of thermoelectric properties of CoSb3-based skutterudites by double filling of Tl and In

Thermoelectric (TE) generators can directly generate electrical power from waste heat, and thus could be an important part of the solution to future power supply and sustainable energy management. The main obstacle to the widespread use of TE materials in diverse industries, e.g., for exhaust heat recovery in automobiles, is their low efficiency in converting heat to electricity. The conversion efficiency of TE materials is quantified by the dimensionless figure of merit, ZT, and the way to enhance ZT is to decrease the lattice thermal conductivity (κlat) of the material, while maintaining a high electrical conductivity, i.e., to create a situation in which phonons are scattered but electrons are unaffected. Here, we report skutterudites filled by Tl and In, Tl0.1InxCo4Sb12, which allow a dramatic reduction of κlat, yielding a ZT of 1.2 at 700 K. We demonstrate that the reduction of κlat is due to the effective phonon scattering induced both by the rattling of Tl and In and by the naturally formed In2O3 n...

Enhancement of thermoelectric properties of CoSb3 skutterudite by addition of Ga and In

Filled skutterudites are known as excellent thermoelectric (TE) materials. The voids in the structure of skutterudites such as cobalt antimonide (CoSb3) can be filled or partially filled with a variety of different atoms. In the present study, we tried to fill both gallium (Ga) and indium (In) into the voids of CoSb3. The polycrystalline samples with nominal compositions of Ga0.2InxCo4Sb12 (x = 0.15, 0.20, 0.25, and 0.30) were prepared and their TE properties were examined from room temperature to 773 K. Ga and In added to CoSb3 partly filled the voids and most of the residual precipitated as nanoparticles at the grain boundaries. A tiny amount of Ga substituted for Sb at the Sb site of CoSb3, while it was more likely for In to fill the voids than Ga. All the samples exhibited negative values for the Seebeck coefficient. The lattice thermal conductivity was reduced effectively by the co-addition of Ga and In without degrading the power factor. The maximum dimensionless figure of merit (ZT) value of 0.95 at 725 K was obtained for the sample with the nominal composition Ga0.2In0.3Co4Sb12.

Preparation, Characterization and Finite Element Computation of Cu(Al1/2Fe1/2)O2 Delafossite-Oxide Themoelectric Generator Module

The CuAl1/2Fe1/2O2 delafossite oxide has been synthesized by solid state reaction method for studying thermoelectric properties and measuring thermoelectric generator output electric power. The Finite Element technique was used to compute the output voltage of thermoelectric generator in applying temperature difference on a single bar and a module model with compared to the measurement results. The measurement results of positive sign Seebeck coefficient confirm the p-type conductor of the sample. The properties of Seebeck coefficient, electrical conductivity, and thermal conductivity are range from 260 to 310μV/K, from 7 to16 S/cm and from 2.5 to 3.5 W/cm-K,respectively, in the temperature range of 300 to 960 K. The output voltage of the single bar in dimension 4.2 × 2.5 × 20 mm3 obtained 0.5 to 3 mV on applying temperature difference from 1 to 10 K closely to the Finite Element result. The computing results of the thermoelectric single bar and module in high temperature reveal the output electric voltage of CuAl1/2Fe1/2O2 oxide raises with the temperature and the number of thermoelectric leg increase. In important results, the high value of electric voltage is obtained 0.2 and 0.4 V for the single bar and the module at 950 K.

Synthesis and Thermoelectric Properties of Cu0.95Pt0.05Fe0.97Sn0.03O2 Delafossite-Oxide

The Cu0.95Pt0.05Fe0.97Sn0.03O2 delafossite sample, which is the simultaneous substitution of the Pt for Cu sites and the Sn for Fe sites of CuFeO2 delafossite, has been investigated the simultaneous effect on electrical conductivity and Seebeck Coefficient for thermoelectric materials due to the previous reports of Cu0.95Pt0.05FeO2 compound displaying high enhancement effect of electric conductivity and the CuFe0.97Sn0.03O2 exhibiting large increasing of Seebeck coefficient. The sample of Cu0.95Pt0.05Fe0.97Sn0.03O2 was synthesized by solid state reaction method. The crystal structure was characterized by XRD, and the valency oxidation state of the sample was evaluated by XPS. The electrical conductivity, Seebeck coefficient, and thermoelectric conductivity were measured in the high temperature range of 320 to 860 K. The measurement results show that, the sign of Seebeck value and result of XPS reveal the sample displaying p-type thermoelectric materials as confirming the simultaneous Pt and Sn-substituted contributing hole carrier. For the effect of simultaneous substitution, the Seebeck coefficient is enhanced in temperature lower than 650 K, while electrical conductivity displays small value in all temperature range. In surprising value, the thermal conductivity of the sample is smallest value in all temperature range. Totally, the ZT value of sample is obtained 0.07 at 860K as higher than that of the reference-based. This experiment confirms that the simultaneous Pt-doped and Sn-doped of Cu0.95Pt0.05Fe0.97Sn0.03O2 compound show high ZT value in temperature higher than 700 K.

Effect of Annealing Temperature on Structure and Optical Properties of Ta2O5 Thin Films Prepared by DC Magnetron Sputtering

Tantalum oxide (Ta2O5) films at 400 nm thickness were prepared at room temperature by DC reactive magnetron sputtering. The effect of annealing temperature on film crystallinity, microstructure and optical properties were investigated. In order to indentify the crystalline structure and film morphology, X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM) measurements were performance. The optical properties were determined by UV-Vis spectrophotometer and spectroscopic ellipsometry (SE). The result showed that, with the annealing treatment at high temperature (700-900°C), the as-deposited films were crystallized to orthorhombic phase of tantalum pentaoxide (β-Ta2O5). In addition, the transmittance spectrum percentage indicated 87%, which corresponded to the obtained optical characteristic. The refractive index varied at 550 nm from 2.17 to 2.21 with increased of the annealing temperature.

High temperature thermoelectric properties of delafossite CuBO 2

CuBO₂ is prepared by a solid-state reaction method to investigate thermoelectric properties in high temperature. The XRD result confirms the CuBO₂ compound existing in this method. The Seebeck reveals the compound displays p-type thermoelectric material. The experimental results of electrical resistivity exhibited results of 0.004 S/cm to 0.038 S/cm with the temperature range of 650 to 830 K. The Seebeck value is in the range of 450 μV/K to 950 μV/K, and the thermal conductivity is in the range of 1.4 × 10^-5 to 5.3 × 10^-5 W/m-K² with the same temperature. The maximum PF and ZT is 5.3 × 10^-5 W/m-K² and 0.0016, respectively, at 960 K. This work demonstrates that the CuBO₂ delafossite-oxide compound displays the p-type thermoelectric materials.