Abstract
The metastable nanocrystalline y form of gallium oxide has been prepared and its microstructure and thermochemistry have been studied for the first time by employing X-ray and electron diffraction, high-resolution transmission electron microscopy, adiabatic and differential scanning calorimetry. The randomly oriented crystallites of maximum 5 nm in size have been observed. The sponge-like morphology of γ-Ga 2 O 3 particles may explain the high specific surface area, previously reported for this material. The defect spinel-type structure of γ-Ga 2 O 3 is similar to that of y and η-Al 2 O 3 . Up to 5.7 wt.% of water can be stored in γ-Ga 2 O 3 and subsequently released at elevated temperatures. Dry γ-Ga 2 O 3 specifically absorbs atmospheric water at room temperature. The transformation of γ-Ga 2 O 3 into stable β-Ga 2 O 3 occurs in two steps. In the range 650-800 K, γ'-Ga 2 O 3 is formed in the course of a reversible higher-order phase transition. The latter irreversibly transforms into β-form above 873 K. The enthalpy of this exothermic transformation is determined as -19.3 ± 0.4 kJ . mol -1 . The coefficients of the Gibbs energy equation for y and γ'-Ga 2 O 3 have been assessed.
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