Synthesis of Gallium Oxide Hydroxide Crystals in Aqueous Solutions with or without Urea and Their Calcination Behavior

Gallium oxide hydroxide (GaOOH· x H₂O) single crystals were synthesized in aqueous solutions by using two different precipitation techniques: homogeneous decomposition of urea and forced hydrolysis in pure water. Precipitation of crystals started at exactly the same pH value (i.e., 2.05 at 85°C) in both cases. The morphology of crystals turned out to be quite different (zeppelin-like with urea, rodlike without urea) in each of the above methods. Calcination of these gallium oxide hydroxide crystals in air at temperatures ≥500°C transformed them into Ga₂O₃. Characterization of the samples was performed by X-ray diffractometry, scanning electron microscopy, thermogravimetry/differential thermal analysis, Fourier transform infrared spectroscopy, and ICP, carbon, and nitrogen analyses.