Anisotropic electrical transport studies of Ca3Co4O9 single crystals grown by the flux method

Single crystals of cobaltite Ca3Co4O9 having sizes up to 10×6×0.2 mm3 were grown by the flux method. The morphology, structure and composition of the crystals were analyzed by scanning electron and atomic force microscopy, X-ray diffraction and energy-dispersive X-ray analysis, respectively. The results revealed that stoichiometric single crystals of Ca3Co4O9 grow via a two-dimensional layer-by-layer mechanism. The temperature dependences of in-plane (ρab) and out-of-plane (ρc) electrical resistivities were measured in the temperature range 30-300 K. ρab(T) exhibited a metal-to-semiconductor transition at around 80 K. Analysis of the semiconducting region revealed the opening of an energy gap of ∼10 meV. On the other hand, ρc(T) showed semiconducting behavior over the whole temperature range with a crossover from 3D to 1D variable range hopping conduction at ∼120 K. The temperature dependence of magnetization revealed two transitions at 30 and 19 K.