The　nonequilibrium　epitaxial　growth　process　of　MgxCa1-xO　solid-solution　films　at　600　degrees　C　is　carefully　investigated.　No　obvious　phase　separation　is　observed　until　annealing　at　800　degrees　C　despite　a　large　miscibility　gap.　The　solid-solution　film　is　featured　with　disorder　alloy　as　confirmed　by　transmission　electron　microscopy　(TEM).　Spinodal　decomposition　caused　by　uprising　diffusion　happens　after　short-time　annealing　which　explicitly　indicates　the　structure　stability　of　the　metastable　solid-solution　films　does　result　from　diffusion　quenching.　(c)　2007　American　Institute　of　Physics.