Controlled Crystal Growth of Indium Selenide, In2Se3, and the Crystal Structures of alpha-In2Se3

In2Se3 has been known for over 100 years and recently attracted interest as a promising candidate for a variety of applications, such as solar cells, photodiodes, and phase-change memories. Despite the broad concern for possible uses, its polymorphism and structure are poorly characterized. By combining X-ray diffraction, transmission electron microscopy, and quantum-chemical calculations, we present here the crystal structures of two layered room-temperature polytypes: 3R and 2H In2Se3. Both polymorphs are stacking variants of the same Se-In-Se-In-Se layers comprising two coordination environments for the In atoms, one tetrahedral and one octahedral. By using chemical-bonding analysis, we look at the different In positions in alpha-In2Se3 and compare them to those in the metastable beta-phase.