The structures were solved with ShelXT 54 , using Olex2 as the graphical interface. Further refinement of the crystal structures was performed using SHELXL, which utilizes a full-matrix least-squares method, on F 2 . Such refinements include the necessary modeling of occupational disorder at the divalent alkaline earth metal sites, such that the measured electron density at each site is properly accounted for. The important crystallographic data from the series of structures with the general formula, Ba 2(1 x) Sr 2x CdP 2 , can be found in Table to S6 for the Ba-poor and Ba-rich compositions respectively.