Thermodynamics, structure and kinetics in the system Ga–O–N

Abstract

In situ XAS Nucleation Non-stoichiometry Amorphous oxide Insulator-metal transition a b s t r a c t 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 b-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 b-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 b-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 b-Ga 2 O 3 to a-GaN and of the oxidation of a-GaN to b-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 b-Ga 2 O 3 and a-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 (g-galons) we performed first-principles calculations using density-functional theory. In addition to the ideal cubic g-Ga 3 O 3 N we studied gallium deficient g-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 b-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.

Zinc-gallium oxynitride powders: effect of the oxide precursor synthesis route

“…Since both GaN and Ga 2 O 3 are thermodynamically more stable than the oxynitride phase, the nitridation of Ga 2 O 3 or the oxidation of GaN do not yield to an oxynitride under thermodynamic reaction control [10]. Experimental and theoretical investigations on the ternary system Ga-O-N confirmed that no crystalline or amorphous oxynitride phases appear during these reactions [17]. Synthesis of GaON was successfully obtained by nitridation under NH 3 flow of other gallium precursors such as Ga(OH) 3 [7,12] or NiGa 2 O 4 [5,6].…”

Electrochemical activation of molecular nitrogen at the Ir/YSZ interface

“…This article replaces the version published on 10th January 2011, which contained errors in eqn (9).…”

Amorphous and highly nonstoichiometric titania (TiOx) thin films close to metal-like conductivity

“…Recently Nagarajan et al reported that strongly oxygen decient gallium oxide, GaO x , shows a new type of chemically driven insulator-metal transition, once prepared in an amorphous form by pulsed laser deposition. 1,2 In fact, amorphous phases with a composition roughly described by GaO 1.2 and with electrically insulating behavior showed conductivity jumps of several orders of magnitude upon heating. This phenomenon is related to an internal redox disproportionation reaction, leading to the precipitation and growth of transparent and insulating Ga 2 O 3 nuclei in the GaO x matrix, which loses even more oxygen.…”