High thermoelectric performance in Bi2-xPbxBa2Co2Oy promoted by directional growth and annealing

Abstract

Bi2-xPbxBa2Co2Oy (x=0.0, 0.2, 0.4, and 0.6) misfit compounds were grown by the laser floating zone technique. Microstructural analysis has shown the formation of thermoelectric grains together with high amount of secondary phases. Thermoelectric grains orientation is increased until 0.4Pb, while further substitution drastically destroys the preferential grain orientation. Electrical resistivity is very low compared with the values obtained in sintered materials, spectacularly increasing power factor. Moreover, the performance of these materials was further improved subjecting the as-grown samples to a postannealing step due to the rise of thermoelectric phase content. These microstructural modifications led to a high decrease of electrical resistivity, improving power factor in around a factor two at room temperature, compared with the as-grown samples. Moreover, the low thermal conductivity of the textured annealed samples leads to a maximum estimated ZT value of 0.53 for the 0.2 Pb-doped samples, much higher than the reported in literature.