High‐Temperature Electrical Transport and Thermoelectric Power of Partially Substituted Ca₃Co₄O₉‐Based Ceramics

Abstract

We present high‐temperature electrical transport and thermoelectric power of K and/or La‐doped Ca3Co4O9‐based ceramics. Temperature and doping dependence of electrical transport properties indicate that both K and La substitutions can increase electrical conductivity at a high temperature, which are mainly related to an increase in carrier concentration and carrier mobility. A metallic‐to‐semiconducting transition temperature (T*) can be observed and shifts to a lower temperature as the doping content increases. However, activation energy is almost independent of the doping. All of the samples show positive thermoelectric power, and the temperature dependence of the thermoelectric power exhibits a simple linear behavior at T>T*. Our experimental data indicate that all of the Ca3Co4O9‐based ceramic samples exhibit large thermoelectric power (∼120 to 180 μV/K).

Effects of Eu and Fe co-doping on thermoelectric properties of misfit-layered Ca3Co4O9+δ

“…Thus, the electrical resistivity increases. Similar results were also reported by some groups [11][12][13][14][15][16]28]. As for the x = 0.1 and y = 0.1 sample, its semiconducting-like character is clear at measured temperature.…”

“…Eu, Y, Lu and Dy etc.) can enhance the thermopoower, but also increase the resistivity [11][12][13][14][15][16]. In contrast, doping in Co-site is more complicated due to the intrinsic feature of multiple oxidation states of the transition metals as dopants as well as the presence of two nonequivalent Co sites in the [Ca 2 CoO 3 ] and [CoO 2 ] subsystems [7,9,[17][18][19].…”

Effect of grain size and porosity on phonon scattering enhancement of Ca3Co4O9

“…The Ca 3 Co 4 O 9 composition can be obtained by solid-state [39][40][41][42] coprecipitation of oxalates [43] or various sol-gel methods [44][45][46]. The sol-gel method is one of the best synthesis methods that yield homogeneous nano-particles [47,48].…”

Waste Thermal Energy Harvesting (I): Thermoelectric Effect

“…Therefore, the increase in the figure of merit due to the doping is moderate. Codoping of with La increases electrical conductivity, without significant effect on Seebeck coefficient [154].…”

“…Both sodium (Na) and potassium (K) have been used to relapse Ca of Ca 3 Co 4 O 9 and Ca 3 Co 2 O 6 [144,148,154,155]. Na is also used as a codopant with other elements, such as Mn and Nd, because single-doping with Na has very weak effect in increasing the Seebeck coefficient of Ca 3 O 4 O 9 [144,[155][156][157].…”