Spontaneous stoichiometry change in single crystals of superconducting (Ba 1-x K x )Fe 2As 2 grown by a rapid-heating Sn-flux method

Abstract

To prevent the loss of K in growing single crystals of Ba 1-x K x Fe 2As 2 we developed a rapid-heating Sn-flux method. Large single crystals with the optimal superconducting transition temperature T C≈38 K were obtained and their structural, chemical and superconducting properties were investigated. Additionally, the effect of post-growth annealing on these crystals at different temperatures was examined. Scanning electron microscopy microprobe studies on a crystal with the composition goal of Ba 0.25K 0.75Fe 2As 2 revealed a well defined separation of two phases with compositions that are suggestive of rational ratios of the K and Ba content. © 2008 Springer Science+Business Media, LLC.