Effect of Laser Wavelength on the Thermoelectric Properties of Bi1.6Pb0.4Sr2Co2O8 Textured Ceramics Processed by LFZ

Bi1.6Pb0.4Sr2Co2O8 samples have been textured by the Laser Floating Zone (LFZ) process using Nd:YAG, and CO2 laser radiation. Using different wavelengths resulted in significant structural and microstructural modifications. Powder XRD patterns showed that the thermoelectric phase is the major one in both cases. Microstructural studies revealed that all samples presented the same phases but with much lower content of secondary ones in those processed with the CO2 laser. Electrical resistivity showed different behavior for the two types of samples, being in general, lower for the CO2 grown rods. Seebeck coefficient is lower for the CO2 grown samples up to 300 degrees C, and higher in the high-temperature range, reaching 240 mu V/K at 650 degrees C, which is one of the highest values obtained so far in these compounds. Moreover, thermal conductivity at 600 degrees C for these samples (0.93 W/ K m) is among the lowest reported in the literature. As a consequence, ZT values at 600 degrees C reached 0.42 in CO2 textured materials, about two times higher than the obtained in Nd:YAG ones. This value is among the highest reported so far in the literature, and is comparable to the performance attained for the same composition containing nanoparticles addition. All these properties, combined with the fact that the processed materials can be directly integrated into thermoelectric modules, render them highly attractive for industrial production.