Dehydroxylation and structural transition in α‐GaOOH investigated by in situ X‐ray diffraction.

Ga2O3 is an ultra‐wide‐bandgap semiconductor that is receiving considerable attention due to its promising applications in high‐frequency, high‐power and high‐temperature settings. It can be prepared by calcinating the α‐GaOOH phase at high temperatures. Understanding the significance of hydroxyl groups in α‐GaOOH, dehydroxylation and the structural transition at high temperatures has become a key aspect of preparing high‐quality α‐Ga2O3 crystals, but the underlying mechanism remains unknown. In this research, α‐GaOOH nanorods were hydrothermally synthesized and the structural evolution of α‐GaOOH investigated at high temperatures by in situ X‐ray diffraction. The hydroxyl group in α‐GaOOH squeezes Ga3+ from the center of the [GaO6] octahedron, resulting in deformed [GaO6] octahedra and significant microstrain in α‐GaOOH. The hydroxyl groups are peeled off from α‐GaOOH when the temperature exceeds 200°C, resulting in contraction along the c‐axis direction and expansion along the a‐axis direction of α‐GaOOH. When the temperature exceeds 300°C, the Ga—O bond inside the double chains preferentially breaks to generate square‐wave‐like octahedron chains, and the neighboring chains repack to form hexagonal‐like octahedron layers. The octahedron layers are packed up and down by electrostatic interaction to generate the α‐Ga2O3 structure. This work highlights the role of hydroxyl groups in α‐GaOOH, dehydroxylation and the structural transition on the atomic scale, providing valuable guidelines for the fabrication of high‐quality α‐Ga2O3 crystals. [ABSTRACT FROM AUTHOR]