Low temperature thermoelectric properties of K-substituted Bi2Sr2Co2Oy ceramics prepared via laser floating zone technique

In the present study, Bi2Sr2-xKxCo2Oy (x = 0.0, 0.050, 0.075, 0.100, and 0.15) ceramic precursors have been produced using the classical ceramic route, followed by texturing through the laser floating zone technique. XRD results show that the thermoelectric phase is the major one in all cases. Moreover, K-substitution decreases the secondary phases content, when compared to the undoped sample. SEM observations indicate that grain orientation is significantly enhanced when K-content is increased. K-doping decreases electrical resistivity from 32 10(-5) Omega m (in undoped samples) to 20-22 10(-5) Omega mat 300 K, while increasing Seebeck coefficient from 55 mu V/K to 100-117 mu V/K at 300 K. On the other hand, thermal conductivity is slightly lower in undoped samples (0.93 W/K m, compared to 1.10-1.28 W/K m for doped ones at 300 K), due to their lower electrical conductivity. Finally, ZT values are higher when the K-content increases up to x = 0.10, reaching 0.029 at around 400 K, and slightly decreasing for higher doping levels.