Effects of addition of Bi2Ca2Co2O y on the thermoelectric properties of Ca3Co4O9 polycrystalline ceramics

Thermoelectric properties of Ca3Co4O9 polycrystalline ceramics with sheet grains were optimized by adding Bi2Ca2Co2O (y) phase. Therefore, the (1 - x) Ca3Co4O9/x Bi2Ca2Co2O (y) (0 <= x <= 1) composites were prepared. The phase constitution and micro-structure of the samples were analyzed by XRD and SEM, respectively. With the addition of Bi2Ca2Co2O (y) , the apparent density D (a) and the relative density D (r) of the samples continuously increases. When x <= 0.4, the electrical resistivity of the samples declines, however, when x >= 0.4, the electrical resistivity of the samples increases. The Seebeck coefficient of the samples grows with the increase of the x monotonously. The power factor of the 0.6 Ca3Co4O9/0.4 Bi2Ca2Co2O (y) samples reaches 0.24 mW m(-1)K(-2) at 973 K. Thermal conductivity kappa of the 0.6 Ca3Co4O9/0.4 Bi2Ca2Co2O (y) monotonously decreases with the temperature rising, achieving the minimum about 1.34 W m(-1)K(-1) at 973 K. The ZT of 0.6 Ca3Co4O9/0.4 Bi2Ca2Co2O (y) composites gets to 0.18, which is comparable to that of most doped Ca3Co4O9 polycrystalline ceramics, implying higher ZT can be realized by combining the strategy of doping and introducing the Bi2Ca2Co2O (y) .