High temperature thermoelectric properties of ceramics.

The Na doping effects on the high temperature thermoelectric properties of ( = 0, 0.05, 0.10, 0.15, 0.20 and 0.30) ceramics were investigated from 343 K to 973 K. When , the electrical resistivity of decreases with increasing Na doping amount due to the hole-doping effect, which exhibits metallic electrical conductivity behavior. While, at the temperature range of 480-830 K, the samples with exhibit semiconductor electrical conductivity behavior instead. The Seebeck coefficients are improved by Na doping at lower temperature, but they decrease slightly at higher temperature except for . Roughly, the thermal conductivity is depressed by the doping defects. As an overall result, the dimensionless figure of merit of reaches the maximum value of 0.3 K at 973 K, which is nearly twice the value of the undoped sample . [ABSTRACT FROM AUTHOR]