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 Co₂O₆^6- chains separated by Ca²⁺ ions. The resistivity (ρ) along the c-axis decreases rapidly with increasing temperature from 2 x 10⁴ to 8 mΩcm in a temperature region of 300-1073 K. The Seebeck coefficient (S) is positive and is 230μV/K and 160μV/K at 373 and 1073 K, respectively. The thermal conductivity (K) 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.