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

Single crystals of cobaltite Ca3Co4O9 having sizes up to 10 x 6 x 0.2 mm(3) 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 (rho(ab)) and out-of-plane (rho(c)) electrical resistivities were measured in the temperature range 30-300 K. rho(ab)(T) exhibited a metal-to-semiconductor transition at around 80 K. Analysis of the semiconducting region revealed the opening of an energy gap of similar to 10 meV. On the other hand, rho(c)(T) showed semiconducting behavior over the whole temperature range with a crossover from 3D to 1D variable range hopping conduction at similar to 120K. The temperature dependence of magnetization revealed two transitions at 30 and 19 K. (c) 2005 Elsevier B.V. All rights reserved.