High temperature thermoelectric properties of oxide Ca/sub 9/Co/sub 12/O/sub 28/

In recent years, more and more attention has been put on oxides as thermoelectric materials. In this work, we synthesized the oxide Ca/sub 9/Co/sub 12/O/sub 28/, analyzed its structure, and measured its electrical properties and Seebeck coefficient from room temperature to 700/spl deg/C. Both the electrical conductivity and the Seebeck coefficient increase with the increasing of temperatures. The electrical conductivity is 83.4 S/cm at 700/spl deg/C. The Seebeck coefficient is negative, and the value is 117.9 /spl mu/V/K at 700/spl deg/C. The calculated values of the power factor increase with increasing temperature, and reach 1.2/spl times/10/sup -4/ W/K/sup 2/.m at 700/spl deg/C. The thermal conductivity at room temperature is 1.93 W/m.K and decreases slightly with increasing temperature. At 700/spl deg/C, the figure of merit is 0.7/spl times/10/sup -4/ K/sup -1/. The substitution of Ca by Bi results in a great improvement of the thermoelectric performance with Z=2.0/spl times/10/sup -4/ K/sup -1/ at 700/spl deg/C.