Spontaneous stoichiometry change in a single crystal of (Ba1-x Kx)Fe2As2 produced by rapid heating method

To prevent the loss of K in growing single crystals of Ba1-x Kx Fe2 As2 we developed a rapid heating Sn-flux method. Large single crystals with the optimal superconducting transition temperature TC about 38K were obtained and their structural, chemical and superconducting properties were investigated. Additionally, the effect of post growth annealing at different temperatures were also examined on these crystals. Scanning electron microscopy microprobe studies on a samples with the composition goal of Ba.25 K.75 Fe2 As2 revealed a sharp separation of two phases with compositions that are suggestive rational ratios of the K and Ba content.