Effect of the Addition of Copper Particles on the Thermoelectric Properties of the Ca3Co4O9 + \u03b4 Ceramics Produced by Two-Step Sintering

A I Klyndyuk,R S Latypov,V M Kononovich,S V Shevchenko,E A Chizhova

doi:10.1134/s0036023622020073

A I Klyndyuk, R S Latypov + Show 3 more

Open Access

https://doi.org/10.1134/s0036023622020073

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Abstract

Composite thermoelectric materials based on layered calcium cobaltite Ca3Co4O9 + δ doped with copper particles were synthesized by two-step sintering, and their microstructure, and electrotransport and thermoelectric properties were studied. It was determined that the introduction of copper particles into the ceramics improves their sinterability at moderate sintering temperatures (Tsint ≤ 1273 K), leading to a decrease in the porosity of the samples and an increase in their electrical conductivity and power factor, whereas the oxidation of copper to less conductive copper(II) oxide significantly decreases the electrical conductivity and power factor of the ceramics sintered at elevated temperatures (Tsint ≥ 1373 K). The power factor is maximum for the Ca3Co4O9 + δ + 3 wt % Cu ceramic sintered at 1273 K (335 μW/(m K2) at a temperature of 1100 K), which is by a factor of 2.3 higher than the power factor of the base material Ca3Co4O9 + δ with the same thermal history (145 μW/(m K2) at 1100 K) and more than 3 times higher than the power factor of the Ca3Co4O9+δ ceramic synthesized by the conventional solid-phase method.

Highlights

Layered calcium cobaltite Ca3Co4O9+δ has both high electrical conductivity σ and Seebeck coefficientS, and low thermal conductivity λ
We studied the effect of the addition of copper particles on the microstructure, and electrotransport and functional properties of thermoelectric Ca3Co4O9 + δ ceramics obtained by twostep sintering
P is maximum for the Ca3Co4O9 + δ + 3 wt % Cu sample sintered at 1273 K and is 335 μW/(m K2) at 1100 K, which is by a factor of 2.3 higher than the power factor of the copper-unmodified Ca3Co4O9+δ ceramic with the same thermal history (P⊥,1100 = 145 μW/(m K2)) and is by a factor of 33 higher than that for the high-porosity

Summary

INTRODUCTION

An alternative method to produce Ca3Co4O9 + δ ceramics with reduced porosity and, as a consequence, elevated electrical conductivity is two-step sintering [9–13] In this case, at the first step, samples are sintered at high temperatures (1373–1473 K). We studied the effect of the addition of copper particles on the microstructure, and electrotransport (electrical conductivity and Seebeck coefficient) and functional (power factor) properties of thermoelectric Ca3Co4O9 + δ ceramics obtained by twostep sintering. The electrical conductivity of the sintered ceramics was measured at direct current (I ≤ 50 mA) by the four-point probe method (V7-58 and V7-53 digital voltmeters, B5-47 current source) in air in the temperature range 300–1100 K in dynamic mode at a heating and cooling rate of 3–5 deg/min with an error of δ(σ) ≤ ±5%.

RESULTS AND DISCUSSION

CONCLUSIONS

CONFLICT OF INTEREST