Preparation And Microfabrication Of Bismuth Telluride Thermoelectric Materials

Bismuth telluride (Bi₂Te₃)-based alloys are one of the most widelystudied and used thermoelectric materials, whose thermoelectric propertiesare better than other materials. Currently, much attention has been paid to theimprovement of the thermoelectric properties of Bi₂Te₃ and the preparation ofits thermoelectric micro-devices. The Bi₂Te₃ was chosen as thermoelectricmaterial in this thesis. The synthesis of Bi₂Te₃ powders and thethermoelectric properties of Bi₂Te₃ compacts as well as the electrophoreticdeposition micro-preparation technology were systematically studied.Firstly, we synthesized fine-grained Bi₂Te₃ powders by using themechanical alloying, and then prepared the bulk samples by using the sparkplasma sintering method. The influence of MA time on the thermoelectricproperties was also investigated. Furthermore, the nano-SiC particles weredispersed in the Bi₂Te₃ to improve the thermoelectric properties. The resultsshowed that MA process produced very fine Bi₂Te₃ particles, whose particlesize ranged from 1 to 2μm. The sample with the MA time of 12h exhibitedthe best thermoelectric properties among those pure Bi₂Te₃ samples. Thenano-SiC dispersion in the Bi₂Te₃ matrix increased the Seebeck coefficientand reduced the thermal conductivity, resulting in an improvement ofthermoelectric properties. The maximum ZT value was obtained in the 0.1vol% SiC-Bi₂Te₃ sample, which is 0.66 around 440K. This value is higherthan that of the Bi₂Te₃ sample without SiC dispersion.Using the MA synthesized Bi₂Te₃ powders as the starting materials, wefabricated the Bi₂Te₃ thick-films by using an electrophoretic depositionmethod. In this study, the effects of electrophoretic deposition factor, such assolution, electrode, substrate, voltage, current, on deposition film weresystematically studied. The results showed that crack-free and smooth Bi₂Te₃thick-films were deposited on silicon wafers, which were stuck on a Taelectrode in acetone solution under the condition of 100V, 3mA, with adepositing time for 10min. The Bi2Te3 thick-films were well sintered at 773Kfor 10min in an Ar atmosphere using a rapid-annealing furnace.In this study, we successfully deposited Bi2Te3 powder into the 60μm-diameter micro-hole array in a silicon wafer under the optimal electrophoreticdeposition condition. This established a technical basis of the preparation ofthe thermoelectric micro-devices through silicon molding process.