Effect of annealing and potassium substitution on the thermoelectric and magnetic properties of directionally grown Bi2Sr2Co2Oy ceramics

Bi2Sr2−xKxCo2Oy (x=0.0, 0.025, 0.050, 0.075, 0.100, 0.125, and 0.15) ceramic materials have been fabricated using a classical ceramic process, followed by texturing through directional solidification. SEM analysis of samples, before and after annealing has shown that grains were aligned along the growth direction. While as-grown samples have several phases, besides the thermoelectric one, the annealed ones show much higher thermoelectric phase content. In addition, K-substitution increases the thermoelectric phase content and enhances grain orientation. These improvements decrease the electrical resistivity without significant changes in Seebeck coefficient. The maximum power factor value for 0.10K-substituted annealed samples has been found as 0.20mW/K2m. This is superior to the highest reported for hot-pressed materials. However, all samples have similar magnetic properties.