Abstract
Ca3−xLaxCo4O9+δ (x=0, 0.05, 0.10, 0.15 and 0.25) ceramic samples were prepared under two-step external magnetic field during both processes of sol–gel and pre-press, and the influence of La doping and external magnetic field on their microstructure and electrical transport properties has been investigated systematically. Due to La-doping, both the Seebeck coefficient (S) and resistivity (ρ) were increased simultaneously, which resulted in a slight improvement of the power factor (PF). After using external magnetic field, the textured structures of all the samples were enhanced dramatically, as a result, the electrical resistivity were substantially decreased. For example, the ρ value for the sample with x=0.15 subjected to the magnetic field was about 25.46% smaller than for the corresponding sample without magnetic field at room temperature. Moreover, the Seebeck coefficient can be improved by increasing spin-orbital degeneracy of Co4+ ions under external magnetic field. These combined effects resulted in observable enhancement of PF over the entire temperature range. Thus, the application of magnetic field can effectively improve electrical transport properties of Ca3Co4O9+δ based materials.
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