Effect of B4C addition on mechanical and electrical properties of Ca3Co4O9

Abstract B4C added Ca3Co4O9 in different proportions (0, 0.1, 0.25, 0.5, and 0.75 wt.%) have been fabricated using solid-state method. Powder XRD patterns have shown that only Ca3Co4O9 phase can be identified in all the samples. Microstructural observations have allowed determining that B4C compound has been superficially oxidized, producing liquid B2O3 phase during sintering, which has reacted with the Ca3Co4O9 grains to produce bridges between them. In spite of the increase of porosity, these bridges led to an important raise (more than two times) of mechanical properties. On the other hand, while B4C addition has not significantly influenced S values, it has decreased electrical resistivity, thermal conductivity, and thermal expansion. Consequently, ZT values have been also increased, reaching 0.24 in 0.25 wt.% B4C containing samples, which is very close to the best values reported in the literature for Ca3Co4O9 compounds, and two times higher than the obtained in pure materials in this work.