Effects of Forming Pressure and Doping on the Properties of Na_(1.4)Co_2O_4-Based Materials

Na1.4Co2O4-based thermoelectric materials were prepared by sol-gel method,where the Na-site doping was done separately with Sr and Li in different amounts of 0.1,0.2,0.3 and 0.4.The effects of forming pressure and doping on the thermoelectric properties of the materials were investigated,such as the electric conductivity,Seebeck coefficient and power factor.The phase composition of the materials was analyzed by XRD.The results showed that the principal crystalline phase of the prepared Sr/Li-doped Na1.4Co2O4-based materials is γ-Na1.4Co2O4.The electric conductivity,Seebeck coefficient and power factor of the materials can all be increased obviously by increasing the forming pressure and Li-doping.When the doping amount of Li is 0.4,the power factor of the materials prepared under 310A4!MPa comes up to 7.44A4!mW·m-1·K-2,which is much higher than that of the materials without doping.The thermoelectric properties of Na1.4Co2O4-based materials can also be improved to a certain extent by Sr-doping in proper amount.