Structural Transformation of Unconventional-Phase Materials

The structural transformation of materials, which involvestheevolution of different structural features, including phase, composition,morphology, etc., under external conditions, represents an importantfundamental phenomenon and has drawn substantial research interest.Recently, materials with unconventional phases that are differentfrom their thermodynamically stable ones have been demonstrated topossess distinct properties and compelling functions and can furtherserve as starting materials for structural transformation studies.The identification and mechanism study of the structural transformationprocess of unconventional-phase starting materials can not only providedeep insights into their thermodynamic stability in potential applicationsbut also offer effective approaches for the synthesis of other unconventionalstructures. Here, we briefly summarize the recent research progresson the structural transformation of some typical starting materialswith various unconventional phases, including the metastable crystallinephase, amorphous phase, and heterophase, induced by different approaches.The importance of unconventional-phase starting materials in the structuralmodulation of resultant intermediates and products will be highlighted.The employment of diverse in situ/operando characterization techniques and theoretical simulations in studyingthe mechanism of the structural transformation process will also beintroduced. Finally, we discuss the existing challenges in this emergingresearch field and provide some future research directions.