Transport properties of p-type Ca3-xLnxCo4O9-Ag (Ln = Lu,Yb; 0.1≤x≤0.2) oxides

Thermoelectric transport properties of p-type Ca_3-xLn_xCo₄O₉/yAg oxides (Ln = Lu & Yb; 0.1 ≤ x ≤ 0.2; 0.05 ≤ y ≤ 0.1) synthesized by sol-gel methodology were investigated in this paper. The structural analyses (SEM, XRD and TEM) confirmed the presence of two phases, viz, Ca_3-xLn_xCo₄O₉ and Ag-metallic phases. The contribution of rare earth doping in one hand and presence of Ag as secondary phase on the other hand were studied. The resistivity measurements indicated the reduction of electrical resistance at the grain boundary leading to an overall decrease in electrical resistivity with increasing Ag-concentration. The enhancement of Seebeck coefficient is attributed to the substitution of Ln³⁺ at Ca²⁺ sites that in turn reduces hole concentration through formation Co³⁺ for charge concentration counter balance in Ca_3-xLn_xCo₄O₉/yAg matrix. The tuning of electrical transport properties through Ca_3-xLn_xCo₄O₉ and Ag-metallic bi-phasic formation resulted high power factor of 582 μW m^?1 K^?2 for Ca_2.8Ln_0.2Co₄O₉/0.05Ag and 548 μW m^?1 K^?2 for Ca_2.8Yb_0.2Co₄O₉/0.05Ag at 950 K highlighting its potential application on small scale energy harvesting to power sensor and wireless sensor network where requirement of power is in the milliwatt range.