Etude des propriétés diélectriques des phases MAX par spectroscopie de pertes d'énergies des électrons

Noël Haddad 1
1 Spectroscopie Electronique
LEM - ONERA - CNRS - Laboratoire d'étude des microstructures [Châtillon]
Abstract : The optical properties of Ti2AlN and Ti2AlC were determined in the 2-80 eV energy range by electron energy loss spectroscopy and in the visible-ultraviolet range, from 1.6 to 5.5 eV, by spectroscopic ellipsometry. Both experimental techniques are angular resolved and in very good agreement over their overlapping energy range. We observe a dependence of the dielectric function as a function of the crystallographic orientation of the crystals. In particular, we notice a shift of the energy position of the plasmon absorption of Ti2AlC with respect to Ti2AlN. Moreover, a drastic change is also observed in the shape of the dielectric function as a function of the composition or valence electron concentration . The dielectric functions are fitted to an empirical semiclassic Drude-Lorentz model to obtain physical parameters such as the relaxation times. These microscopic parameters are then used in a macroscopic model to yield the transport properties such as the static conductivity as function of the crystal orientation. Ti2AlN is found to be a better conductor than Ti2AlC in all orientations, which is consistent with experimental measurements. A comparison of the electrical and optical properties of these two compounds is made in terms of different electronic properties and interband-intraband transitions deduced from our model.
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Noël Haddad. Etude des propriétés diélectriques des phases MAX par spectroscopie de pertes d'énergies des électrons. Science des matériaux [cond-mat.mtrl-sci]. Université Paris Sud - Paris XI, 2009. Français. ⟨tel-00662325⟩

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