Synthesis and characterization of (Ba, Sr)Fe2(As, P)2 iron pnictide superconductors

► We made polycrystalline samples of (Ba0.5Sr0.5)Fe2(As1−xPx)2 ((BaSr)122:P) superconductors. ► Structural and superconducting properties were investigated. ► The sample with x = 0.4 showed the highest Tc of 29 K, being nearly identical to those of Ba122:P and Sr122:P. ► The structure of the Fe2(As, P)2 block was almost identical regardless of different alkaline earth elements.