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LaCoO3 displays a high Seebeck coefficient that makes it a potential candidate for future thermoelectric applications. In this study we provide data on the improvement of the thermoelectric efficiency of LaCoO3 by double substitution with nickel and iron. The improvement is achieved by balancing the opposite effects of nickel and iron ions. Double-substituted perovskites LaCo1–x (Ni0.5Fe0.5) x O3 with compositions having equal amounts (0 < x ≤ 0.25) of Ni and Fe are examined. The perovskites are obtained from freeze-dried citrate precursors at 900 °C. Structural and morphological characterizations are carried out by powder XRD and SEM analyses. The thermoelectric efficiency of the perovskites is determined by the dimensionless figure of merit (ZT) calculated from the independently measured Seebeck coefficient, electrical resistivity, and thermal conductivity. Compared with LaCoO3, the double-substituted perovskites display a higher electrical conductivity which does not depend on the total Ni+Fe content. This is a consequence of the increase in the carrier density. It is shown that the effect of Ni ions (for partial electron delocalization) is more pronounced in comparison with that of Fe ions (for electron localization). The synergic effect of Ni and Fe is demonstrated by the effective reduction of the thermal conductivity in comparison with the single-substituted perovskites. As a result, the perovskite with a composition LaCo0.8Ni0.1Fe0.1O3 exhibits the best thermoelectric efficiency with ZT = 0.16, which is an order of magnitude higher than that of LaCoO3 at room temperature.

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