Defect-Associated Thermoelectric Transport Properties of Dual-Substituted CaMn^sub 1−x^Nb^sub x/2^M^sub x/2^O3 (M = Mo, W; 0.02 ≤ x ≤ 0.06)

We report thermoelectric transport properties of dual-substituted CaMn1−x Nb x/2M x/2O3 (M = Mo, W; 0.02 ≤ x ≤ 0.06) synthesized by conventional solid-state methodology. The electrical resistivity decreases with the increase of the doping level, which indicates an increase in charge-carrier concentration in the system. The increase in carrier concentration leads to the formation of Mn3+ ions with e g 1 electrons in the Mn4+ matrix of CaMn1−x Nb x/2M x/2O3 (M = Mo, W). The electrical resistivity shows non-metal-like temperature dependence. In contrast, the Seebeck coefficient of CaMn1−x Nb x/2M x/2O3 (M = Mo, W) initially decreases with temperature up to 550 K and then increases. The dual substitution by pentavalent Nb and hexavalent Mo or W at the Mn-site causes partial reduction of Mn4+ → Mn3+ and produces a defect center in the Mn-sublattice of CaMn1−x Nb x/2M x/2O3 (M = Mo, W). This defect center acts as a static point-like defect center to cause an additional contribution to the entropy of the system which results in an increase of the Seebeck coefficient with temperature. The highest power factor obtained is of 192 μW m−1 K−2 at 950 K for CaMn0.96Nb0.02Mo0.02O3.