Typical nanocomposite heterogeneous ZnSb-Al2O3 and ZnSb-ZnO phase-change materials were prepared. A direct comparison of the distinct structures in the amorphous, metastable, and stable states between two different materials was investigated systematically. Upon heating, ZnSb-Al2O3 films show a two-step crystallization process with the formation of the metastable orthorhombic ZnSb phase ahead of the stable trigonal ZnSb phase, while ZnSb-ZnO films could exhibit a one-step crystallization process with the formation of the stable trigonal ZnSb phase when the ZnO-doping concentration is more than 12.3 atom %. In the case of ZnSb-Al2O3, the structural transition to the metastable phase is accompanied by a pronounced increase in the grain size up to 100 nm. Such an increase in the crystal grain size is not found in ZnSb-ZnO films; i.e., the nanocrystals do not grow significantly when the crystallized film is precipitated with the metastable ZnSb phase. By the method of advanced scanning transmission electron m...