Drastic enhancement of mechanical properties of Ca3Co4O9 by B4C addition

Ca3Co4O9 with B4C additions in different proportions (0, 0.10, 0.25, 0.5, and 0.75 wt.%) have been fabricated using the classical solid-state method. Powder XRD patterns have displayed that Ca3Co4O9 phase is the major one in all samples. Microstructural observations showed that B4C has been superficially oxidized, producing liquid B2P3 during sintering, and reacting 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 when compared to the pristine materials. On the other hand, while B4C addition has not influenced S values, it has decreased electrical resistivity, thermal conductivity, and thermal expansion. Consequently, ZT values have been also increased, reaching 0.24 at 800 degrees C in 0.25 wt.% B4C containing samples, which is very close to the best values reported in the literature, and two times higher than the obtained in pure materials in this work.