Thermoelectric properties of Bi2Sr2Co2Ox polycrystalline materials

Bi2Sr2Co2O9 (BC-2202) polycrystalline materials with a layered structure have been prepared by partial melting. The chemical compositions of the samples are Bi2Sr2Co2Ox (2202), Bi1.8Sr2Co2Ox (Bi-1.8), and Bi2Sr1.8Co2Ox (Sr-1.8). All three samples are p-type conductors. The electric properties, namely, the Seebeck coefficient (S) and electric resistivity (rho), of the samples are dependent on chemical composition. The S values increase with temperature at T > 673 K and, at 973 K, reach 100, 110, and 150 mu V K-1 for the 2202, the Bi-1.8, and the Sr-1.8 samples, respectively. Thermal conductivity (kappa) for all samples is lower than for ordinary conducting oxides. The figure of merit (Z) increases with temperature for all samples. Z values at 973 K are 0.77x10(-4), 0.61x10(-4), and 2.0x10(-4) K-1 for the 2202, Bi-1.8, and Sr-1.8 samples, respectively. The thermoelectric properties depend on the chemical composition of the BC-2202 phase. The BC-2202 material thus appears to be a promising thermoelectric material due to its high performance at high temperature (similar to 1000 K). (C) 2000 American Institute of Physics. [S0003-6951(00)02217-8].