Enhancement of ZT by incorporation of large single crystals of Ca3Co4O9 in a Ca3Co4O9

Recently, large single crystals of (Ca2CoO3)CoO2 (Co-349) possessing high thermoelectric properties have been synthesized using a flux method in a high yield of about 30%. This makes possible to prepare Co-349 composites consisting of Co-349 single crystals and powder. Electrical resistivity p of the composite including the single crystals of 20 wt.% is lower than that of the bulk material without the single crystals. Improvement of the grain alignment and an effect of current bypassing grain boundaries through the large single crystals in the composite may suppress rho and, in consequence, thermoelectric figure of merit ZT is elevated up to 0.55 at 973 K in air.