Anek Charoenphakdee

Crystal-structure dependent domain-switching behavior in BaTiO3 ceramic

Crystal-structure dependent dynamic scaling behavior was investigated for BaTiO3 ceramic. The scaling relation of the form 〈 〉∝ Af E mn 0 , (where 〈〉 A is the area under the hysteresis loop, while f and E0 represent the frequency and amplitude of the applied electric field signal) was used to determine the values of parameters m and n at various temperatures in the range of �90 °C to 170 °C. The variations in the values of parameters m and n with temperature are explained in terms of the effect of the crystallographic nature of BaTiO3. The values of parameters m and n obtained for the paraelectric regime suggest that the hysteresis in the P–E (polarization–electric field) loops is related to the dielectric loss rather than any domain-related phenomenon.

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.

Thermoelectric Properties and Power Generation of p–Ca3Co4O9 and n–Sr0.87La0.13TiO3 Thermoelectric Modules

The Ca3Co4O9 (CCO) and Sr0.87La0.13TiO3 (SLTO) are good property of oxide thermoelectric (TE) materials. They synthesized by solid state reaction (SSR) method to study thermoelectric properties and fabrication of thermoelectric module. It was found that, synthesis of CCO shows that Seebeck coefficient, electrical resistivity, thermal conductivity and values are 130 μV K–1, 8.31 mΩ cm, 0.82 W m–1 K–1 and 0.08, respectively at 473 K. The Seebeck coefficient, electrical resistivity, thermal conductivity and ZT values of SLTO are –359 μV K–1, 2.9 mΩ m, 18.09 W m–1 K–1 and 1.13×10–3, respectively at 473 K. TE modules of CCO and SLTO were fabricated by ultra sonic soldering method. The power generation of TE modules were measured with temperature difference (ΔT) of 10–180 K. The 1 pair and 2 pairs TE modules for a maximum power generation of matching load are 19 k and 30 k, respectively. The maximum output power of 2 pairs TE module is larger than 1 pair TE module about two times.

Effect of Strong Correlation of Mg2+-doped into Cr3+ Sites of CuCrO2 on Thermoelectric Properties

This study aims to investigate the strong correlation effect of spin and charge carriers for the Mg2+-substituted into Cr3+ sites of CuCrO2 delafossite on thermoelectric properties. The CuCr0.98Mg0.02O2 sample was synthesized by a solid state reaction. The starting powder CuO, Cr2O3 and MgO were ball milled with poly vinyl alcohol solution for 24 h. The ball milled powder was pressed and sintered in air atmosphere at temperature 1050 C for 6 h. The crystal structure was characterized by XRD, TGA, XPS and the thermoelectric properties were measured at high temperature. The XRD displayed peaks of the pure phase CuCrO2 structure as hexagonal delafossite-type structure space group: Rm. The Seebeck coefficient of the samples displayed positive sign as p-type (hole) conductor. The XPS results displayed Mg2+, Cu1+, Cr3+ and Cr4+ ion states. The Mg2+ induced mixed-valance Cr3+/Cr4+ states resulting in enhanced Seebeck coefficient due to a strong correlation of the spin-entropy. The experimental results of Seebeck value were close to calculated results by the extended Heikes formula confirming of the strong correlation effect. In addition, the Mg-doped CuCrO2 resulted in increased electrical conductivity and reduced thermal conductivity with increasing temperature. These indicate that the Mg2+-substituted for Cr3+ of CuCrO2 delafossite enhance the thermoelectric properties.

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.

Reinvestigation the Thermal and Electrical Transport Properties of Tl7Sb2

The authors examined the thermal and electrical transport properties of Tl7Sb2 at temperatures ranging from room temperature to 400 K. The crystal system of Tl7Sb2 is cubic with the lattice parameter a = 1.16053 nm and the space group is Im3m. The polycrystalline samples were prepared by melting stoichiometric amounts of thallium and antimony. Although, usually the thermal conductivity of thallium compounds is very low (<1 Wm-1K-1), that of Tl7Sb2 was relatively high (~13 Wm-1K-1 at room temperature). This is because of the large electronic contribution to the thermal conductivity.