Ammonothermal conversion of cyclotrigallazane to GaN: Synthesis of nanocrystalline and cubic GaN from [H₂GaNH₂]₃

Under ammonothermal conditions, cyclotrigallazane, [H₂GaNH₂]₃, was converted to nanocrystalline GaN. The coherent length of the GaN product could be controlled by manipulating reaction time and temperature. Nanocrystalline GaN powders with average crystallite sizes of 3-17 nm were produced in the temperature range of 150-450 °C. Analysis of the powders by XRD and TEM indicated that the nanocrystals possessed a structure composed of a random arrangement of cubic and hexagonal close packed planes. The addition of NH₄I to the reaction mixture resulted in the isolation of bulk samples of phase pure, cubic GaN at temperatures as low as 200 °C. The synthesis of the cubic phase was found to be temperature dependent, with mixtures of cubic and hexagonal GaN being produced at temperatures greater than 350 °C.