Thermal sublimation of atomically homogeneous Zn x Cd1_x S powders from a single source results in films that are nonuniform in a direction normal to the substrate. This is attributed to initial preferential sublimation of Cd from the charge and is verified by energy dispersive x-ray analyses of film cross sections and of the charge residue. These results are related to the utility of this technique for forming Zn x Cd1_x S films for photovoltaic applications.