Preparation and Electric Properties of Sr-doped and Cr-doped NaCo_2O_4 Thermoelectric Materials

NaCo2O4 is a potential thermoelectric material due to its good electric properties. Doping can affect the physical and chemical properties of materials. In this paper, NaCo2O4 thermoelectric materials with Na-site doping by Sr and Co-site doping by Cr are prepared by self-flux method. The effect of two doping elements and their amounts on the electric properties of NaCo2O4 are investigated by XRD phase composition analyzing and electric properties measurements of the samples. As a result, both Sr and Cr can increase Seebeck coefficients of the materials. When doping amount of each element reaches at 0.3, the Seebeck coefficients are to a maximum value of 180 μVK-1for Sr and 185 μVK-1for Cr at 823 K, respectively. When Sr doping amount is x=0.1, the increase of the Seebeck coefficient is greater than the decrease of electric conductivity, so as to the power factor of NaCo2O4increase(the maximum value is 870 μWm-1K-2at 823 K) although their electric conductivities decrease, indicating the thermoelectric properties of NaCo2O4 can be improved effectively by regulating the amount of Sr.