Ceramic composites based on Ca Co O and La NiO with enhanced thermoelectric properties

Abstract Ceramic composites were produced by combining the oxide materials Ca3Co4−xO9+δ and La2NiO4+δ. Both compounds were characterized by a plate-like crystal shape, but crystal sizes differed by around two orders of magnitude. The composite materials could be successfully prepared by using uniaxial pressing of powder mixtures and pressureless sintering to a porous ceramic. Possible reactions between both materials during sintering were analyzed. The ceramic composites with low amounts of La2NiO4+δ showed enhanced thermoelectric properties, caused by an increasing power factor and simultaneously decreasing thermal conductivity. For the evaluation of the thermoelectric properties, two different types of Ioffe plots were utilized. The maximum figure-of-merit zT at 1073 ​K was 0.27 for the pure Ca3Co4−xO9+δ as well as for the sample containing 5 ​wt% La2NiO4+δ. However, the average Z T ¯ in the temperature range of 373 K to 1073 K could be increased by 20% for the composite material.