Comparison of the high temperature thermoelectric properties for Ag-doped and Ag-added Ca₃Co₄O₉

A series of high-textured Ag-doped or/and Ag-added Ca₃Co₄O₉ ceramic specimens have been prepared by a cold-pressing technique and their thermoelectric properties were compared from room temperature to 1000 K. The substitution of Ag⁺ for Ca²⁺ causes the reduction of resistivity and the enhancement of thermoelectric power simultaneously, whereas the addition of metal Ag results in the decrease on resistivity together with thermoelectric power. Both Ag⁺ doping and Ag addition can enhance power factor; however, the doping of Ag⁺ is advantageous for the suppression of thermal conductivity whereas the addition of Ag facilitates thermal conductivity. Ca_2.7Ag_0.3Co₄O₉/Ag-10 wt% composite exhibits a quite respectable thermoelectric performance; the dimensionless figure of merit ZT can reach 0.5 at 1000 K.