Etude Raman des alliages à base de Be ou N, à liaison fortement contrastées : modèle de percolation

Abstract : We propose a 1 bond->2 modes model for the long wavelength optical phonons in zinc-blende ternary/quaternary alloys, based on the percolation site theory. There is no additional input with respect to the usual 1 bond->1 mode modified-random-element-isodisplacement model, based on a description of the crystal according to the virtual crystal approximation. Our model takes into account the fractal->normal object transition which goes with the dispersion->continuum topology transition at the percolation thresholds of the bonds. The model is built from ternaries and multinaries involving the first row elements in substitution, Be and N, which open the attractive class of mixed crystals with highly contrasted bond stiffness. A simplified version is derived for current alloys which display a much weaker contrast in the bond stiffness. This is tested with GaAs-InAs, taken here as a typical challenging system. The multi-phonon behavior of this alloy is re-examined in the light of percolation model, with much success. In order to gain a microscopic insight to support the percolation model, we performed in collaboration with an inveterate theoricien a first-principles study of the bond properties in a fully relaxed Zn26Be6Se32 supercell with Be Se bonds located in a continuous chain and isolated Be-Se bonds
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Teddy Tite. Etude Raman des alliages à base de Be ou N, à liaison fortement contrastées : modèle de percolation. Autre [cond-mat.other]. Université Paul Verlaine - Metz, 2004. Français. ⟨NNT : 2004METZ031S⟩. ⟨tel-01750079⟩

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