High‐Temperature Electrical Transport and Thermoelectric Power of Partially Substituted Ca ₃ Co ₄ O ₉ ‐Based Ceramics

We present high‐temperature electrical transport and thermoelectric power of K and/or La‐doped Ca 3 Co 4 O 9 ‐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 Ca 3 Co 4 O 9 ‐based ceramic samples exhibit large thermoelectric power (∼120 to 180 μV/K).