Improving thermoelectric properties of Ca₃Co₄O_9+δ through both Na doping and K addition at optimal values

Ca_2.93Na_0.07Co₄O_y/x wt% K₂CO₃ (x = 0.00, 0.01, and 0.03) polycrystalline ceramics were prepared by conventional solid-state method. XRD results have shown that all samples predominantly include Ca₃Co₄O₉ phase together with small amounts of secondary phases. SEM images show that all samples have randomly oriented plate-like grains in different sizes. The electrical resistivity measurement showed that electrical properties of Ca₃Co₄O₉ ceramics can be improved significantly by both, Na doping and K addition at their optimal values. The effect of dopants on thermoelectric properties of Ca₃Co₄O₉ was examined by both, Seebeck coefficient and power factor, being higher in K-added than in the pure samples, indicating that thermoelectric properties of samples are positively affected when alkaline elements enter into their structure.