The misfit-layered cobalt oxide [Ca 2-w CoO 3-d ][CoO 2 ] 1.62 is a promising material for hightemperature thermoelectric heat recovery. Here, we show that discrepancies in the numerously reported thermoelectric performances can result from Co 3 O 4 impurities or a change of the defects, i.e., the relative Co content in the [Ca 2-w CoO 3-d ][CoO 2 ] 1.62 phase. We observe that increasing the relative Co content in the [Ca 2-w CoO 3-d ][CoO 2 ] 1.62 phase leads to a larger figure of merit ZT. We

more »

... attribute this increase of ZT to additional p-type charge carriers introduced by Ca vacancies and the resulting reduction of the electrical resistivity. For Co/Ca ratios above the miscibility limit, the increase in thermal conductivity due to the formation of Co 3 O 4 impurities leads to a reduction of ZT when the volume fraction of the Co 3 O 4 phase is increased from 1% to 3%. Hence, the best figure of merit is expected close to the upper phase boundary of the [Ca 2-w CoO 3-d ][CoO 2 ] 1.62 phase. Published by AIP Publishing. [http://dx.FIG. 3. Effective hole carrier concentration for different amounts of Co 3 O 4 impurity phase. The mobility of the charge carriers is presented in the inset. 215101-6 B€ uttner et al.