Synthesis and characterization of α-, β-, and γ-Ga2o3 prepared from aqueous solutions by controlled precipitation

α, β and γ-Ga2O3 have been successfully obtained in an easily scalable synthesis using aqueous solution of gallium nitrate and sodium carbonate as starting materials without any surfactant and additive. α and β-Ga2O3 were obtained by calcination at 350 and 700 °С, respectively, of α-GaOOH, prepared by controlled precipitation at constant pH 6 and T = 55 °С, with 24 h of aging. Aging was necessary to fully convert the initially preciptated gel into a well-crystalline and phase-pure material. γ-Ga2O3 was obtained after calcination at 500 °С of gallia gel, synthesized at constant pH 4 and T = 25 °С, without aging. These three polymorphs have a for gallia relatively high surface area: 55 m2/g (α-Ga2O3), 23 m2/g (β-Ga2O3) and 116 m2/g (γ-Ga2O3). The combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), nitrogen physisorption and thermogravimetry (TG) was employed to characterize the samples and their formation.

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► α-, β- and γ-Gallia could be prepared by a simple aqueous precipitation route.
► GaOOH is the precursor for α- and β-Gallia and is obtained at high pH and T.
► Precipitate aging is essential for the formation of well-crystalline GaOOH.
► At low pH and temperature the precursor of γ-Gallia is obtained without aging.
► Thermal treatment leads to porous Gallia materials with relatively high specific areas.