This paper investigates the disorder-order phase transition in gallium oxide (Ga₂O₃) from amorphous to γ-Ga₂O₃ and then to β-Ga₂O₃ using in situ transmission electron microscopy (TEM) and ex situ annealing experiments. The study finds that amorphous Ga₂O₃ crystallizes at 470 °C into the γ phase, which undergoes a phase transition to the β phase above 500 °C. Between 500 °C and 900 °C, a mixture of γ-Ga₂O₃ and β-Ga₂O₃ coexists, and above 950 °C, only β-Ga₂O₃ remains. The authors construct a common lattice for both phases, containing an fcc-type oxygen sublattice and cation sites shared by both phases, with partially occupied sites in the γ phase corresponding to interstitial sites in the β phase. They identify the transition as a reconstructive disorder-to-order phase transition mediated by cation exchange to next-nearest neighbor sites. This model explains the formation of γ-Ga₂O₃ during implantation for n-type doping and the subsequent recovery of β-Ga₂O₃ through annealing. The findings provide insights into the atomic mechanisms driving phase transitions in Ga₂O₃ and have potential applications in understanding similar phase transitions in other materials.This paper investigates the disorder-order phase transition in gallium oxide (Ga₂O₃) from amorphous to γ-Ga₂O₃ and then to β-Ga₂O₃ using in situ transmission electron microscopy (TEM) and ex situ annealing experiments. The study finds that amorphous Ga₂O₃ crystallizes at 470 °C into the γ phase, which undergoes a phase transition to the β phase above 500 °C. Between 500 °C and 900 °C, a mixture of γ-Ga₂O₃ and β-Ga₂O₃ coexists, and above 950 °C, only β-Ga₂O₃ remains. The authors construct a common lattice for both phases, containing an fcc-type oxygen sublattice and cation sites shared by both phases, with partially occupied sites in the γ phase corresponding to interstitial sites in the β phase. They identify the transition as a reconstructive disorder-to-order phase transition mediated by cation exchange to next-nearest neighbor sites. This model explains the formation of γ-Ga₂O₃ during implantation for n-type doping and the subsequent recovery of β-Ga₂O₃ through annealing. The findings provide insights into the atomic mechanisms driving phase transitions in Ga₂O₃ and have potential applications in understanding similar phase transitions in other materials.