Electrical transport properties and high-temperature thermoelectric performance of (Ca_0.9M_0.1)MnO₃ (M = Y, La, Ce, Sm, In, Sn, Sb, Pb, Bi)

The electrical transport properties of (Ca_0.9M_0.1)MnO₃(M = Y, La, Ce, Sm, In, Sn, Sb, Pb, Bi) are investigated in terms of a new material for high-temperature thermoelectric conversion. The substitution at the Ca site causes a marked increase in the electrical conductivity σ, along with a moderate decrease in the absolute value of the Seebeck coefficient S. The plots of log σT vs 1/T show a negative linear relation, indicating that hopping conduction occurs in these oxides. The σ values at room temperature increase with increasing ionic radii of the cation substituents, implying an increase in the carrier mobility due to larger intersite distance for hopping. The sample of (Ca_0.9Bi_0.1)MnO₃ attains the largest power factor, 2.8 × 10^-4/W m^-1K^-2, at 800°C and leads to the figure of merit 0.7-0.75 × 10^-4K^-1 over the wide range of temperatures 600-900°C. The oxide shows a maximum ZT value of 0.085 at 900°C.