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, Cd, Dy, Ho) pe rovskites were studied in the temperature range of 373-1173 K. Electrical c onductivity increased and Seebeck coefficient decreased with increasing the ionic radius of rare-earth elements (Ho3+ < Dy3+ < Gd3+ < Sm3+ < Nd3+ < Pr 3+). 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)CoO 3. Electronic contribution to the thermal conductivity also increased with increasing the ionic radius of rare-earth element. (C) 2001 Elsevier Scienc e B.V. All rights reserved.