Electron energy-loss spectra calculations and experiments as a tool for the identification of a lamellar C{sub 3}N{sub 4} compound
- Institut des Materiaux Jean Rouxel, UMR 6502, Universite de Nantes--CNRS, 2, rue de la Houssiniere, 44322 Nantes Cedex (France)
- Institut de Chimie de la Matiere Condensee de Bordeaux, ICMCB-CNRS UPR 9048, 33608 Pessac Cedex (France)
In order to identify a poorly crystallized lamellar C{sub 3}N{sub 4} compound using electron energy-loss spectroscopy, we first concentrate on model compounds, namely, graphite at the carbon K edge and hexagonal boron nitride at both K edges. We show that extremely good agreement can be obtained between experimental spectra and ab initio calculations using the WIEN2k program [P. Blaha, K. Schwarz, P. Sorantin, and S. B. Trickey, Comput. Phys. Commun. 59, 399 (1990)]. Because the calculations are based on the density functional theory considering independent quasiparticles, they are generally believed to be inadequate to rigorously describe the excitation process. Nevertheless, we demonstrate that the spectra, when divided into two regions, above and below the ionization energy, can be simulated over a 50 eV energy range. In these materials, the first region must be simulated taking into account the electronic relaxation around a full core hole. For the second part starting usually 10-12 eV above the threshold, only a very small or no core hole at all should be introduced for the relaxation. Furthermore, we show that an empirical formula is sufficient but necessary to take into account the lifetime of the electron in the excited state. After discussion of these results on model compounds, we clearly identify the limits and benefits of these comparisons and apply them to an unknown structure. The experimental spectra were recorded at low temperature in order to avoid beam damages. They are compared with those calculated for various structures having compositions close to C{sub 3}N{sub 4}. From these core-loss studies, as well as from the corresponding low-loss ones, the structure of our sample is shown to be locally very close to that of the (C{sub 3}N{sub 3}){sub 2}(NH){sub 3} lamellar compound described by Kawaguchi and Noziak [Chem. Mater.7, 257 (1995)]. This structure can also be viewed as a defective hexagonal C{sub 3}N{sub 4} lamellar structure (with ABA stacking), rendering this compound most suitable for a further high-pressure conversion to a superhard 3D C{sub 3}N{sub 4} phase.
- OSTI ID:
- 20788184
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 73, Issue 19; Other Information: DOI: 10.1103/PhysRevB.73.195111; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BORON NITRIDES
CARBON NITRIDES
COMPARATIVE EVALUATIONS
DENSITY FUNCTIONAL METHOD
ELECTRON SPECTRA
ELECTRONS
ENERGY-LOSS SPECTROSCOPY
EV RANGE
EXCITATION
EXCITED STATES
GRAPHITE
HOLES
IONIZATION
LIFETIME
QUASI PARTICLES
RELAXATION
RELAXATION TIME