RuSr2GdCu,0, (Ru-12 12) has a layered structure in which insulating (30, plane and conductive RuO, plane are piled up alternatively. Thermoelectric properties of Ru-12 12 have been evaluated from room temperature to 600 "C and these results are compared with those of SrRuO, with a three dimensional perovskite structure. SrRuO, shows a metallic 0-T behavior, whereas a semiconducting-like transport is observed in the Ru-1212. At temperatures T < 4OO0C, the Seebeck coefficient values of Ru-1212 are larger than those of SrRuO, by more than twice. The thermal conductivity of Ru-1212 is lower than that of SrRuO, whole the measured temperature range. In the viewpoint of Seebeck coefficient and thermal conductivity, making an insulatingkonducting superlattice structure is effective to enhance the thermoelectric performance.
IntroductionConventional thermoelectric materials such as metal chalcogenides [ 1-31, transition metal disilicides [4-61, and SiGe [7-91 alloys are suffered from vaporization, surface oxidation, decomposition and melting at high temperature in