GaO2H, alpha-Ga2O3 and beta-Ga2O3 powders were synthesized from mechanically ground GaN powders with thermal annealing in a nitrogen atmosphere. The structural properties of GaO2H, alpha-Ga2O3 and beta-Ga2O3 powders were investigated by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM). The studies revealed that the samples obtained by ball-milled GaN for 4 h are orthorhombic crystalline GaO2H phase. However, when GaO2H were annealed in a nitrogen atmosphere at 550 and 950 degrees C, alpha-Ga2O3 and beta-Ga2O3 powders were obtained, respectively. SEM images indicated that the morphologies of GaO2H, alpha-Ga2O3 and beta-Ga2O3 are ruleless, and their sizes are in the range of about 300-70, 150-70, and 150-70 nm, respectively. (c) 2005 Elsevier B.V. All rights reserved.