High temperature thermoelectric properties of Bi2−xNaxSr2Co2Oy ceramics

Abstract

The Na doping effects on the high temperature thermoelectric properties of [Formula: see text] ([Formula: see text] = 0, 0.05, 0.10, 0.15, 0.20 and 0.30) ceramics were investigated from 343 K to 973 K. When [Formula: see text], the electrical resistivity of [Formula: see text] 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 [Formula: see text] 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 [Formula: see text]. Roughly, the thermal conductivity is depressed by the doping defects. As an overall result, the dimensionless figure of merit [Formula: see text] of [Formula: see text] reaches the maximum value of 0.3 K at 973 K, which is nearly twice the value of the undoped sample [Formula: see text].