Thermoelectric properties of barium doped calcium cobaltite obtained by simplified chemical route

Abstract

Calcium cobaltite (CCO) thermoelectric ceramics in Ca₃Co₄O₉ and Ca_2.95Ba_0.05Co₄O₉ compositions were produced by a simplified chemical route developed in this study. Undoped ceramics sintered at 1193 K for 12 h presented a bulk density equivalent to 77% of the theoretical density, one of the highest values ever found for conventionally sintered undoped calcium cobaltite. The presence of barium improved densification, reaching 80% of the theoretical density. Thermoelectric properties were discussed based on X-ray diffraction patterns, scanning electron micrographs, Seebeck coefficient, electrical and thermal conductivity. Electrical characterizations presented values of about 6200 and 7000 S/m at 873 K for undoped and doped ceramics, respectively. However, all ceramics presented almost the same range of activation energy values, indicating the possibility of non-effective substitution through this methodology. The maximum global PF (power factor) was 0.10 mW.m^-1.K^-2 for the densest undoped sample and an overall ZT (dimensionless figure of merit) of 0.07 for the undoped ceramic at 873 K.

Keywords:
thermoelectric ceramics; calcium cobaltite; barium