Microstructural refinement and enhanced transport properties in binary doped NdFeAsO superconductor

Abstract

We report the synthesis of Nd1 xCaxFeAsO1 2xF2x superconductors using CaF2 as a binary dopant that provides both holes and electrons by simultaneous substitution of Ca2þ ions and F ions at Nd3þ and O2 sites, respectively. The sample with x¼0.2 exhibits a maximum critical temperature (TC) of 52.3K and transport critical current density (JC) of 1240 A/cm2 at 12 K. An interesting feature observed for binary doped samples is the preferential alignment of (00l) planes and the refinement of microstructure both in terms of grain size and grain connectivity. NdFeAsO based superconductors are already known for their very high critical fields and field independent JC(H) performance. However, the development of the bulk superconductors with oriented large grains and good grain connectivity has not been reported so far and hence the present work will be definitely a step towards the progress in NdFeAsO based conductor development.