RESUMEN
The ammonolysis of beta-Ga(2)O(3) to alpha-GaN and the oxidation of alpha-GaN to beta-Ga(2)O(3) have been studied by means of in situ X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). In situ X-ray absorption measurements on polycrystalline powder particles on the gallium K-edge during both reactions give detailed information about the reaction kinetics. We were able to extract this kinetics by fitting linear combinations of beta-Ga(2)O(3) and alpha-GaN spectra only. The kinetics of the ammonolysis can be described well by an extended Johnson-Mehl-Avrami-Kolmogorow model, while the oxidation kinetics can be modelled by a shrinking core model. Investigations by means of TEM and SEM support the assumptions in both models. Our experimental results and the models are discussed in terms of the reaction energetics and the reaction mechanisms.