Thermoelectric Properties of a Phase-Heterogeneous Ceramic Based on Ca3Co4O9+δ, Prepared by Hot Pressing

A phase-heterogeneous ceramic based on layered calcium cobaltite Ca 3 Co 4 O 9+δ was prepared by solid-phase reactions followed by hot pressing. The phase composition, microstructure, electrical conductivity, and thermoelectromotive force (thermo-emf) of the ceramic were studied, and the power factor ( P ) was calculated. Hot pressing allows preparation of a high-density ceramic with high electrical conductivity, and the phase heterogeneity considerably increases its thermo-emf coefficient, which in total can be considered as a procedure for preparing a ceramic with improved thermoelectric characteristics. The ceramic of the nominal composition Ca 3 Co 4.4 O 9+δ , containing an impurity Co 3 O 4 phase, has the highest power factor ( P 1100 = 427 μW m –1 K –2 ), which is 1.5 times higher than that of Ca 3 Co 4 O 9+δ ( P 1100 = 280 μW m –1 K –2 ) and more than 4 times higher than that of the low-density ceramic Ca 3 Co 4 O 9+δ prepared by the traditional solid-phase method.