Application of sol-gel method in the synthesis of gallium(III)-oxide

Precipitations by hydrolysis of gallium(III)-isopropoxide and from aqueous GaCl3 solution by addition of aqueous tetramethylammonium hydroxide (TMAH) solution were utilized to obtain gallium(III)-oxide precursors. The precursors thus formed and the samples obtained upon heating these precursors at high temperatures were analysed by XRD, FT-IR and TEM. Amorphous phase (dominant) and nanosized α-GaOOH particles (several nanometers in size) were obtained by addition of hot water and TMAH solution to the solution of gallium(III)-isopropoxide dissolved in 2-propanol. A completely amorphous precipitate was obtained by hydrolysis of gallium(III)-isopropoxide with pure water at room temperature, and upon heating this precipitate at 500 °C the nanosized β-Ga2O3 particles (size ∼10 to 20 nm) were obtained. On the other hand, α-GaOOH particles, as a single phase, were obtained by precipitation from aqueous GaCl3 solution with addition of aqueous TMAH solution. These α-GaOOH particles transformed at 500 °C to α-Ga2O3 as a single phase. Upon heating at 900 °C, in all cases only β-Ga2O3 was detected. The size and morphology of the particles in the samples investigated depended on the starting chemicals and the conditions of the experiment. Differences in the mechanism of the precipitation by hydrolysis of gallium(III)-isopropoxide or the precipitation from aqueous solution of GaCl3 by addition of strong organic alkali (TMAH) were suggested.