Journal article

Publication year: 2009

Pages: 132-152

Journal: Progress in Solid State Chemistry

Volume number: 37

Issue number: 2-3

ISSN: 0079-6786

Open access status: Green

DOI Link: https://doi.org/10.1016/j.progsolidstchem.2009.11.005

Publisher: Elsevier

Abstract: 
Within the ternary system Ga-O-N we performed experimental and theoretical investigations on the thermodynamics, structure and kinetics of new stable and metastable compounds.We studied the ammonolysis of beta-Ga(2)O(3) at elevated temperatures by means of ex situ X-ray diffraction, ex situ neutron diffraction, and in situ X-ray absorption spectroscopy (XAS). From total diffraction pattern refinement with the Rietveld method we analyzed the anionic occupancy factors and the lattice parameters of beta-Ga(2)O(3) during the reaction. Within the detection limits of these methods, we can rule out the existence of a crystalline oxynitride phase that is not derived from wurtzite-type GaN. The nitrogen solubility in beta-Ga(2)O(3) was found to be below the detection limit of about 2-3 at.% in the anionic sublattice. The kinetics of the ammonolysis of beta-Ga(2)O(3) to alpha-GaN and of the oxidation of alpha-GaN to beta-Ga(2)O(3) was studied by means of in situ X-ray absorption spectroscopy. In both cases the reaction kinetics could be described well by fitting linear combinations of beta-Ga(2)O(3) and alpha-GaN spectra only, excluding that other crystalline or amorphous phases appear during these reactions. The kinetics of the ammonolysis can be described well by an extended Johnson-Mehl-Avrami-Kolmogorow model with nucleation and growth of GaN nuclei, while the oxidation kinetics can be modeled by a shrinking core model where Ga(2)O(3) grows as a layer. Investigations by means of TEM and SEM support the assumptions in both models. To investigate the structure and energetics of spinel-type gallium oxynitrides (gamma-galons) we performed first-principles calculations using density-functional theory. In addition to the ideal cubic gamma-Ga(2)O(3) we studied gallium deficient gamma-galons within the Constant-Anion-Model.In highly non-stoichiometric, amorphous gallium oxide of approximate composition GaO(1.2) we found at a temperature around 670 K an insulator-metal transition, with a conductivity jump of seven orders of magnitude. We demonstrate through experimental studies and density-functional theory calculations that the conductivity jump takes place at a critical gallium concentration and is induced by crystallization of stoichiometric beta-Ga(2)O(3) within the metastable oxide matrix. By doping with nitrogen the critical temperature and the conductivity in the highly conducting state can be tuned.

Harvard Citation style: Martin, M., Dronskowski, R., Janek, J., Becker, K., Röhrens, D., Brendt, J., et al. (2009) Thermodynamics, structure and kinetics in the system Ga-O-N, Progress in Solid State Chemistry, 37(2-3), pp. 132-152. https://doi.org/10.1016/j.progsolidstchem.2009.11.005

APA Citation style: Martin, M., Dronskowski, R., Janek, J., Becker, K., Röhrens, D., Brendt, J., Lumey, M., Nagarajan, L., Valov, I., & Börger, A. (2009). Thermodynamics, structure and kinetics in the system Ga-O-N. Progress in Solid State Chemistry. 37(2-3), 132-152. https://doi.org/10.1016/j.progsolidstchem.2009.11.005