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

A phase-heterogeneous ceramic based on layered calcium cobaltite Ca3Co4O9+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 Ca3Co4.4O9+δ, containing an impurity Co3O4 phase, has the highest power factor (P1100 = 427 μW m–1 K–2), which is 1.5 times higher than that of Ca3Co4O9+δ (P1100 = 280 μW m–1 K–2) and more than 4 times higher than that of the low-density ceramic Ca3Co4O9+δ prepared by the traditional solid-phase method.