TY  - JOUR
AU  - Martin, M.
AU  - Dronskowski, R.
AU  - Janek, J.
AU  - Becker, K.-D.
AU  - Roehrens, D.
AU  - Brendt, J.
AU  - Lumey, M.W.
AU  - Nagarajan, L.
AU  - Valov, I.
AU  - Börger, A.
TI  - Thermodynamics, structure and kinetics in the system Ga-O-N
JO  - Progress in solid state chemistry
VL  - 37
SN  - 0079-6786
CY  - Oxford [u.a.]
PB  - Pergamon Press
M1  - PreJuSER-9108
PY  - 2009
N1  - Financial support by the German Research Foundation (DFG Priority Program 1136, Substitutional Effects in Ionic Solids) is gratefully acknowledged. The authors would like to express their gratitude to A. Shenyshin and M. Hoelzel (FRIVIII, Garching) for their support during the neutron measurements at the SPODI diffractometer, M. Lerch (FU Berlin) for the quantitative analysis of nitrogen and oxygen via the hot gas extraction method, G. Heger, G. Roth and K. Sparta (AIXTAL, Aachen) for support in all crystallographic matters, E. Welter, K. Rickers, A. Webb and D. Zajac (all HASYLAB @ DESY) for support during the beam times, R. Zaunbrecher for making the SEM measurements, F. Dorn and T. Weirich
AB  - 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-Ga2O3 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-Ga2O3 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-Ga2O3 was found to be below the detection limit of about 2-3 at.% in the anionic sublattice. The kinetics of the ammonolysis of beta-Ga2O3 to alpha-GaN and of the oxidation of alpha-GaN to beta-Ga2O3 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-Ga2O3 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 Ga2O3 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-Ga2O3 we studied gallium deficient gamma-galons within the Constant-Anion-Model.In highly non-stoichiometric, amorphous gallium oxide of approximate composition GaO1.2 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-Ga2O3 within the metastable oxide matrix. By doping with nitrogen the critical temperature and the conductivity in the highly conducting state can be tuned. (C) 2009 Elsevier Ltd. All rights reserved.
KW  - J (WoSType)
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000273097800005
DO  - DOI:10.1016/j.progsolidstchem.2009.11.005
UR  - https://juser.fz-juelich.de/record/9108
ER  -