Abstract
The effect of cationic composition and sintering conditions on the electrotransport and thermoelectric properties of Ca3CoxO (x = 3.8, 4.0, and 4.2) had been investigated. It had been found that increase of cobalt oxide content in the samples increase their electrical conductivity, creation of phase inhomogeneity improves their thermo-EMF coefficient, and sintering above temperature of peritectoid decomposition increase their apparent density, which, in the whole, improves thermoelectric properties of ceramics based on the layered calcium cobaltate Ca3Co4O . So, power factor values of phase inhomogeneous ceramics Ca3Co4.2O , sintered in air below and above temperature of peritectoid decomposition of Ca3Co4O , at 800℃ were equal 255 and 273 respectively, which was 2.1 and 2.4 times larger than for the Ca3Co4O . It had been also found that sintering of phase inhomogeneous ceramics both in oxidizing or reducing atmospheres resulted in improving of its functional properties. So, power factor values of Ca3Co3.8O (sintered in oxygen at 970℃) and Ca3Co4.2O (sintered in nitrogen at 920℃) at 800℃ were equal 422 and 378 respectively, which was 3.5 and 3.1 times larger than for the Ca3Co4O .
Highlights
The growth of global energy consumption and the negative environmental impact of many modern energy conversion technologies have led to increased activity in the search for alternative energy sources
The indicated drawbacks are largely absent for oxide thermoelectrics, including materials based on the layered calcium cobaltate Ca3Co4O9+δ, which in recent years are considered as a promising basis for the development of p-branches of high-temperature thermoelectric generators [2, 3]
The aim of this work was to study the influence of the cationic composition and thermal prehistory of ceramics based on Ca3Co4O9+δ on its phase composition, physicochemical and functional properties, as well as to study the possibility of improving the thermoelectric characteristics of materials based on the layered calcium cobaltate by creating of phase inhomogeneity in it
Summary
The growth of global energy consumption and the negative environmental impact of many modern energy conversion technologies (for example, the burning of hydrocarbon fuels) have led to increased activity in the search for alternative energy sources. The functional (thermoelectric) characteristics of ceramics based on the Ca3Co4O9+δ can be essentially improved by using instead of the traditional ceramic methods the “soft” low-temperature synthesis methods [4, 5], using special techniques for sintering ceramics – hot pressing [6], spark plasma sintering [7,8,9], and by partial substitution of calcium ions in it by bismuth [3, 10,11,12] or rare earth elements ions [3, 13, 14] or of cobalt ions by 3d-metal ions [3, 15, 16] It was shown in [11, 17,18,19] that thermoelectric characteristics of oxide ceramics can be improved by creating phase inhomogeneity in it
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