High-temperature thermoelectric properties of single-crystal Ca3Co2O6

We measured the high-temperature thermoelectric properties of single-crystal Ca3Co2O6, which consists of parallel one-dimensional Co2O66− chains separated by Ca2+ ions. The resistivity (ρ) along the c-axis decreases rapidly upon increasing temperature from 2×104 to 8 mΩ cm in a temperature region of 300 to 1073 K. The Seebeck coefficient (S) is positive and is 230 and 160 μV/K at 373 and 1073 K, respectively. The thermal conductivity (κ) is as low as 8 W/mK at room temperature and decreases linearly with the increase of temperature to 4.6 W/mK at 773 K. Thus, the estimated dimensionless figure-of-merit [ZT=(S2/ρκ)T (T: absolute temperature)], is about 0.15 at 1073 K. As the thermoelectric figure-of-merit (Z), shows a sharp rise in the measured temperature range, Ca3Co2O6 is expected to possess high thermoelectric efficiency at higher temperatures, and is considered to be a potential candidate for use as a thermoelectric material at high temperatures by virtue of being chemically stable up to 1300 K.