The effect of environmental conditions on the mechanical and thermoelectric properties of Bi2Ca2Co1.7Ox textured rods

The effect of environmental conditions on the microstructural, mechanical and thermoelectric properties of highly textured Bi2Ca2Co1.7Ox thermoelectric materials was investigated by powder X-ray diffraction, scanning electron microscopy, three point bending test, electrical resistivity, and thermopower measurements. Textured thin rods were directionally grown from the melt through a laser floating zone melting technique. The mechanical and thermoelectric properties of Bi2Ca2Co1.7Ox were determined as a function of two different environmental conditions, air and water. Flexural strength data showed that these oxide materials possess an unsuspected degradation resistance. These good results have been related to the presence of a very thin (~250 µm) low porosity region and relatively small grain sizes, which avoids the internal degradation by water infiltration through the porosity. Moreover, thermoelectric performances, evaluated through the power factor are maintained practically unchanged, independently of the environmental conditions.