Self-Limited Growth of Nanocrystals in Structural Heterogeneous Phase-Change Materials during the Heating Process

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 microscopy, we clearly find that the grain growth is limited by the separated ZnO domain formation, which improves the amorphous thermal stability significantly with the optimized 10-year data retention ability up to 229.2 degrees C for (ZnSb)(81.8)(ZnO)(18.2) film.