Granularity and annealing effects in superconductivity of the electron doped cuprate system Nd_1.85Ce_0.15CuO₄

We have observed large granular effects in the superconducting behavior of the electron doped cuprate Nd_1.85Ce_0.15CuO₄ synthesized in polycrystalline form by solid state reaction. The resistive transition to the superconducting state reveals a staged behavior due to intra and inter-granular transitions, the former corresponding to superconductivity within the grains and the latter due to long range coherence between the grains. On the other hand the DC magnetization reveals the intrinsic behavior of the grains and a smooth transition from the paramagnetic state to the diamagnetic.Our investigations of electrical current dependence of inter and intra-granular transitions indicatesignificant changes in the former without any change in the latter. The behavior is in line with what is expected in granular superconductors which are related to intra granular and inter granular coupling. Scanning electron microscopy investigations provide morphological evidence of granularity in the material.