Decrease of Ca3Co4O9+δ thermal conductivity by Yb-doping

Abstract

In this study, the effect of Yb-substitution on the structural, electrical and thermal transport properties of the Ca 3 Co 4 O 9 þ δ system has been investigated in the low temperature region (between 10 and 300 K). The resistivity of samples increases with raising the Yb-concentration in the system. All the samples show a metal-semiconductor transition below 85 K. In the analysis based on Strongly Correlated Fermi Liquid Model, an increased bandwidth and a reduced electronic correlation are found. It has also been found that the energy gap, E 0 , value also decreases with Ybsubstitution. The samples show positive thermoelectric power, indicating that dominant charge carriers are holes in all the samples. The thermoelectric power value decreases with Yb-substitution. From Mott equation, it is determined that the Fermi energy and hole concentration decrease in the Yb-susbtituted samples, compared to the undoped ones. Thermal conductivity, κ, is decreased in about 50% of the measured in undoped samples for the 0.01 and 0.03 Yb-doped samples at 300 K. Highest figure of merit, ZT, value is found to be 5.4 10 À 3 at 300 K for the unsubstituted sample and the ZT value decreases by the substitution.

Significant enhancement of the thermoelectric performance in Ca3Co4O9 thermoelectric materials through combined strontium substitution and hot-pressing process

“…In the first situation, Yb modifies the rock-salt layer size (raising ρ and S) and charge (decreasing the Co 4+ proportion, increasing S and ρ). Moreover, its high atomic mass enhances phonon scattering, leading to lower thermal conductivity [20]. This is a more complex situation than in isovalent substitution, where only modifications in the rock-salt layer dimensions, and effects on the phonon scattering, are present.…”