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Investigation of Thermoelectric Performance and Power Generation Characteristics of Dual-Doped Ca1–xRE′x/2RE″x/2MnO3 (RE′/RE″ = Dy, Gd, Yb, Lu; 0.05 ≤ x ≤ 0.1)

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journal contribution
posted on 08.06.2018, 00:00 by Rapaka S. C. Bose, Abanti Nag
The dual-doped Ca1–xRE′x/2RE″x/2MnO3 (RE′/RE” = Dy, Gd, Yb, Lu; 0.05 ≤ x ≤ 0.1) based n-type thermoelectric oxides were synthesized by the sol–gel methodology. The sol–gel method of synthesis lowered the sintering temperature; this enhanced the density of the system close to the theoretical value. Rare-earth doping at the Ca site drastically reduced the electrical resistivity by 2 orders of magnitude, compared to that of undoped CaMnO3. This was due to the formation of Mn3+ (t2g3eg1) ions with eg1 electrons in the Mn4+ (t2g3eg0) matrix of Ca1–xRE′x/2RE″x/2MnO3. The temperature dependence of electrical resistivity revealed a change from semiconductor to metallic at lower doping levels (Ca0.95RE′0.025RE″0.025MnO3), while at higher doping levels (Ca0.9RE′0.05RE″0.05MnO3) the ρ­(T) curve had a semiconducting nature in the entire temperature range. In contrast, the Seebeck coefficient showed linear temperature dependence for all the compositions. The power factor (PF) of Ca1–xRE′x/2RE″x/2MnO3 (RE′/RE” = Dy, Gd, Yb, Lu; 0.05 ≤ x ≤ 0.1) was much higher than the PF of undoped CaMnO3 and the highest PFs obtained were 530 μW m–1 K–2 for Ca0.95Dy0.025Yb0.025MnO3 and 580 μW m–1 K–2 for Ca0.9Lu0.05Yb0.05MnO3 at 950 K. The proof-of-concept experiment of power generation with Ca3Co4O9 as p-type element resulted in a power output of 160 μW at 500 °C for a unicouple module.