Influence of ionic size of rare-earth site on the thermoelectric properties of RCoO3-type perovskite cobalt oxides

Thermoelectric properties of Ca-doped RCoO3 (R=Pr, Nd, Sm, Gd, Dy, Ho) perovskites were studied in the temperature range of 373–1173 K. Electrical conductivity increased and Seebeck coefficient decreased with increasing the ionic radius of rare-earth elements (Ho3+<Dy3+<Gd3+<Sm3+<Nd3+<Pr3+). At low temperatures, Seebeck coefficient (p-type) was fairly high for all compositions and attained low and constant values at high temperatures indicating semi-metallic behavior. Similar phenomena were observed when the ionic radius of dopants (Ca2+<Sr2+<Ba2+) increased for (Pr0.9Ca0.1)CoO3. Electronic contribution to the thermal conductivity also increased with increasing the ionic radius of rare-earth element.