Synthesis and properties of materials based on layered calcium and bismuth cobaltites

Abstract

Materials based on layered calcium (Ca3Co4O9 + δ) and calcium-bismuth (Bi2Ca2Co1.7O y ) cobaltites were derived based on a technique of solid-phase reactions. Their thermal expansion, electrical conductivity, and thermoelectric power were found. It was demonstrated that these materials are p-type semiconductors with a coefficient of linear thermal expansion (11.4–12.8) × 10–6 K–1. It was found that the phase separation of the material leads to a reduction in the electrical conductivity and an increase in the Seebeck coefficient and power factor, which reaches its maximum value (0.24 mW m–1 K–2 at T = 1100 K) for materials containing approximately equal amounts of phases Ca2.7Bi0.3Co4O9+δ and Bi2Ca2Co1.7O y . Ffunctional characteristics of the thermoelectric material are evidence of its promising use in high temperature thermoelectric generators.