Thermoelectric Characteristics of N-type Bi-Te Materials by Powder-Based Sintering Process
Authors: Koo Hye Young , Ha Gook Hyun , Park Min Soo 
Published: February 2020

Thermal technology is one by using the Seebeck and the Peltier effect of converting thermal energy and electrical energy to each other reversibly by utilizing the semiconductor material used in power generation and cooling technology. The technology has been attracting attention as one eco-friendly energy technology that can improve energy conversion efficiency. The energy conversion efficiency of thermoelectric materials are presented by ZT, which is the dimensionless figure of merit, ZT = [(σα2)T]/κ where σ is electrical conductivity, α is Seebeck coefficient, T is absolute temperature, and κ is electronic and phonon thermal conductivity, respectively.
Bismuth-telluride-based alloys are widely used as thermoelectric materials because of its high thermoelectric performance ZT near the room temperature in 273~473K As thermoelectric systems are constructed by connecting pairs of p-type and n-type materials in series, it is necessary to improve the performance of both p- and n-type materials to increase the value of ZT. For the Bismuth-telluride based alloys materials, research on improving the performance of n-type material is necessary because it is lower than that of p-type material. To improve the thermoelectric performance, materials with a high electrical conductivity (σ) and low thermal conductivity (κ) are required. Research on adding dopants to improve the electrical conductivity or on material nanostructuring, dispersed.
In this study, In order to improve the performance of the n-type materials, the improvement of the characteristics was carried out by using the powder-based sintering process
Considering the anisotropy of the synthesized thermoelectric materials, their physical properties were measured in both the vertical and horizontal directions with respect to the pressure direction. XRD (D/Max 2500, Rigaku) was used to analyze the phase characteristics of the sintered bodies, and the microstructural characteristics of the fracture surfaces of the sintered bodies were analyzed using a field-emission scanning electron microscope (FESEM, JSM- JEOL). To measure the electrical characteristics of the thermoelectric materials, the Seebeck coefficient and electrical conductivity were measured at temperatures ranging from room temperature to 423 K using the four-probe method (ZEM-3, Ulvac-Riko). The thermal conductivity was obtained by multiplying the thermal diffusivity, the specific heat of a sample, and its density after taking samples from the sintered bodies and measuring the thermal diffusivity using the laser flash method (LFA-467, Netzsch Co.). In this case, the average value of the specific heats of the samples of 0.167 was used, which was obtained by measuring the specific heats of multiple specimens using DSC (Pyris-1, Perkin Elmer). In addition, samples were taken from the sintered bodies, and their carrier concentrations and mobilities were measured through the Hall effect using the van der Pauw method (HMS-3000, Ecopia).
Keyword : Bi2Te3, Thermoelectric materials, Powder, Sintering