Effects of KCl Addition on the K2CO3Flux Growth of Ca3Co4O9Crystals for a Thermoelectric Device

Crystals of Ca3Co4O9 were grown by a solution method. We found that an appropriate amount of KCl addition to the K2CO3 flux can facilitate the growth of Ca3Co4O9 crystals and suppress the crystallization of Ca3Co2O6, which is the decomposed phase of Ca3Co4O9. Using a flux composition of K2CO3:KCl=4:1, we obtained large single Ca3Co4O9 crystals possessing a well-grown ab-plane. The largest crystal formed had a size of about 4.5×2.5×0.02 mm3. The in-plane electrical resistivity and Seebeck coefficient at 300 K are 12 mΩcm and 150 µV/K, respectively. The Seebeck coefficient exhibited is slightly larger than previously reported values.