Evaluation of Thermoelectric Properties of Cu_(3.21)Bi_(4.79)S_9 Bismuth Chalcogenide

摘要

Cu_(3.21)Bi_(4.79)S_9 was synthesized from Cu, Bi and S element powders using mechanical alloying method. The formation of Cu_(3.21)Bi_(4.79)S_9 was identified using XRD and the changes of morphologies of the mixtures of Cu, Bi, and S powders during milling were observed using table top SEM. The milled powders were sintered using Hot-isostatic pressing at 230°C with a pressure of 50 MPa. Electrical resistivity and Seebeck coefficient of sintered samples were measured using ZEM-3 (Electrical resistivity and Seebeck Coefficient measuring System). Cu_(3.21)Bi_(4.79)S_9 and some secondary phases were found in the 5h milled powder but single phase Cu_(3.21)Bi_(4.79)S_9 was only obtained after milling for 15 h. A minimum electrical resistivity of sintered Cu_(3.21)Bi_(4.79)S_9 sample was found to be 0.66 Q.m at 170°C. We observed that a n- to p-type conversion at temperature of around 75°C. However, a maximum n-type Seebeck coefficient of Cu3.21Bi4.79S9 was of-214 uV/K at 45°C. The Seebeck coefficient decreases with increasing temperature and it reaches zero value at around 75°C and then p-type Seebeck coefficient increases with increasing the temperature. The maximum p-type Seebeck coefficient was observed of 202 uV/K at 170°C.