Enhanced thermoelectric properties in Bi2Sr2-xBaxCo2Oy via doping and texturing for integration in more efficient thermoelectric generators

Abstract

Bi₂Sr_2-xBa_xCo₂O_y (0 ≤ x ≤ 0.15) thermoelectric samples have been sintered, and textured through the laser floating zone process using a Nd:YAG laser. Powder XRD studies showed that the thermoelectric phase is the major one in all cases, with higher amount of secondary phases in the textured ones due to their incongruent melting. Microstructural characterization revealed a drastic microstructural modification in the textured samples, when compared to the sintered ones, producing much larger and well oriented grains along the growth direction. These characteristics led to lower electrical resistivity in textured samples, reaching the minimum at 650 °C (14.8 mΩ cm) in 0.125Ba-doped samples, which is lower than those typically reported in this system. On the other hand, no significant variation in Seebeck coefficient has been found between the samples. This behaviour is associated to the isovalent doping which does not modify the charge carrier concentration in the material, and the highest values at 650 °C (166 μV/K) are in the order of the reported in the literature. As a consequence, power factor values are mainly driven by the electrical resistivity values, leading to the highest values at 650 °C in 0.125Ba-doped textured samples (0.19 mW/K²m) due to their lowest resistivity. These values are higher than the reported for textured materials and in the order of the best reported for this compound in bulk form. All these properties, together with the possibility of the direct integration of these compounds in thermoelectric modules, make them very attractive for practical applications ensuring access to affordable, reliable, and sustainable energy for all.