Synthesis, mechanical and magnetic properties of transition metals-doped Ca3Co3.8M0.2O9

We report the synthesis of a thermoelectric oxide Ca3Co4O9 using a sol–gel method with polyvinyl alcohol as the dispersion agent. The transition metals (Cr, Fe, Ni, Cu and Zn) were doped at the Co-site to form Ca3Co3.8M0.2O9. The single phases of the doped Ca3Co3.8M0.2O9 were confirmed by thermogravimetric and differential thermal analysis, and X-ray diffraction patterns. Relatively high porosity was observed in scanning electron micrographs. The density of the samples was the highest for Cu-doped Ca3Co3.8M0.2O9 (78% of the theoretical density). The Young's modulus and shear modulus measured by the sound velocity method were found to be in the order of tens of GPa, and also found to be highly correlated to the density of the samples. The magnetic properties of the transition metals-doped Ca3Co3.8M0.2O9 were found to be insensitive to the doping and all sintered samples showed paramagnetic behaviour, with susceptibility of ∼10−6 emu/(Oe g), at room temperature.