Preparation And Mechanical Properties Of N-Type Bismuth Telluride Thermoelectric Materials

Thermoelectric material is a functional material that can be used to convert thermal energy into electrical energy directly with carriers. It has a long performance life and good stability and environmental benign. Bi2Te3-based solid solutions exhibit the best thermoelectric performance around room temperature and have been widely used for cooling and temperature control in various areas. Bi2Te3-based materials have a rhombohedral structure with space group R3m, and are generally grown by means of zone melting, Bridgman and Czochralsky techniques due to the strong anisotropies on thermoelectric properties. The unidirectionally solidified ingots have the most excellent thermoelectric performance along the crystal growth direction. However, the poor mechanical property due to the lamellar crystallographic structure and weak Van der Waals bonding between Te-Te layers causes difficulties in fabrication process and potential problems in the reliability for the applications especially in the miniature thermoelectric modules. MSP (Modified Small Punch) tests are evaluation methods for mechanical properties by using small specimens, which are appropriate for ceramic materials since they combine the characteristics of small punch tests and biaxial bending tests. Testing with small specimens of square or disk samples, MSP tests have many advantages including very small specimens, easy preparation of samples, proper place of samples during tests even at elevated temperatures, and accurate determination of plastic deformation displacement at higher temperatures, so the methods have been widely employed in ambient and high-temperature evaluation of mechanical properties of ceramic materials.In this research, starting with the commercialized zone melted n-type Bi2Te3 material; we employed spark plasma sintering (SPS) technique to obtain densified bulk material. The measurement of electrical conductivity and laser flash system were used to characterize the n-type Bi2Te3 bulk materia. Results indicated that at the room temperature(300K), the power factor (α2σ) were 30.6×10-4W/mK2(400℃), 31.2×10-4W/mK2(420℃) and 30.8×10-4W/mK2(440℃), respectively. The ZTmax of SPS-400℃sample could resch 0.79 at 405K.MSP was first used to research Bi2Te3 bulk materials. Corresponding to the preparation of 400℃,420℃,440℃, n-type Bi2Te3 bulk materials at room temperature of the MSP strength were 104MPa,108MPa and 119MPa, respectively. Furthermore, zigzag load-deflection curves could be observed in MSP tests from Bi2Te3 bulk materials. MSP tests are quite competitive in fatigue estimation since it is convenient to fix specimens.