ABSTRACT
The anisotropic structure of Bi2Te3-type thermoelectric materials makes them prone to mechanical vulnerabilities and inconsistent electrical and thermal properties according to microstructural orientation. In this study, sintered BiSbTe bodies were synthesized by spark plasma sintering (SPS), hot pressing (HP), and hot isostatic pressing (HIP) using p-type thermoelectric powders produced through oxide reduction. Changes in the microstructure and thermoelectric properties were investigated according to the sintering process. The thermoelectric properties of the samples produced by uniaxial methods (SPS and HP) were affected by the direction of pressing during sintering; the electrical and thermal conductivities differed by up to 30% depending on the orientation. In contrast, the hydrostatic HIP process did not impart such directionality; the difference in thermoelectric properties according to orientation was significantly reduced to less than 4%. Moreover, the sintered Bi2Te3 body produced by HIP showed outstanding thermoelectric performance at a much lower temperature than the samples produced by SPS or HP, with a maximum figure-of-merit (ZT) of 1.42 at 373 K.
ABSTRACT
In order to establish thinner dielectric layers in thick film electronic components such as MLCC (Multilayer ceramic capacitor), BaTiO3 nanoparticles have been utilized. However, studies on the synthesis of nanoparticles smaller than 20 nm, the characteristics of the BaTiO3 powder, and the powder's sintering are lacking. Therefore, this paper aims to synthesize BaTiO3 particles smaller than 20 nm by using the molten salt method and evaluate the microstructure and dielectric properties by varying the sintering temperature from 750 degrees C to 1200 degrees C. Through the molten salt method and by using KOH-KCl mixed salt, 20 nm BaTiO3 powder was synthesized at a low temperature of 150 degrees C. Sintering the pellets formed from the synthesized 20 nm BaTiO3 nano powder led to the observation of an unusual phenomenon where the particles grew to approximate sizes below 850 degrees C where densification progressed. At sintering temperatures above 950 degrees C, particles that expanded into rod shapes were observed and these particles were identified to be unreacted TiO2 based on the results of the EDX (Energy Dispersive X-ray Spectroscopy) analysis and phase analysis results.
ABSTRACT
In this study, bismuth telluride (Bi2Te3)-based nanopowders with particle size ranging from 100 to 300 nm are prepared by high-energy ball milling. Then, the prepared nanopowders are homogeneously mixed with organic binders to form a paste; this paste is used as the raw material to prepare thick-film thermoelectric modules. The thick film prepared by screen printing followed by hot pressing of p-type pastes show reproducible thermoelectric properties, exhibiting an electrical resistivity of 2.0 m Omega cm and a Seebeck coefficient of 298 muVK-1. The prepared p-type Bi2Te3 thick film has a high power factor because its Seebeck coefficient is significantly higher than that of Bi2Te3 based-bulk materials. These results indicate that a thick film prepared from bismuth telluride nanopowders has potential for use as high-performance thermoelectric modules in practical applications such as power generation and cooling system in electronic devices.
