We model Ba In Figure , DG m is negative for all values of x suggesting the formation of a complete solid solution. More interestingly, our calculations reveal site selectivity of the disorder depending on whether the alloy composition is Ba-rich (x < 0.5) or Sr-rich (x > 0.5). Specifically, we find that for Ba-rich compositions (x < 0.5), it is energetically more favorable to fully occupy site 1 with Ba while confining Ba/Sr disorder to site 2 as compared to fully occupying site 2 and confining disorder to site 1. Disorder on both sites 1 and 2 is energetically even more unfavorable for all x < 0.5 and x > 0.5. Similarly, for Srrich compositions (x > 0.5), the full occupancy of site 2 by Sr and confining Ba/Sr disorder to site 1 is energetically favorable. This site selectivity is a direct consequence of the relative ionic size of Ba and Sr and the space available in the interlayer and intralayer sites of the layered structure of Ba 2(1 x) Sr 2x CdP 2 . Figure shows the site selectivity for representative Ba-rich (x = 0.2) and Sr-rich (x = 0.8) compositions.