Etude par spectroscopie Raman de l'ordre polaire et des transitions de phase dans les solutions solides de KTa1-x NbxO3 (KTN)

Abstract : This work concerns experimental investigations about the influence of defects on the mechanism of phase transitions in solid solutions of KTa1-x NbxO3 (KTN). The aim is to understand the changes in the properties of the pure sample KTaO3 and the phase transition process which are induced by niobium doping. We have performed dielectric, optical (light diffraction and transmission) measurements and mainly Raman scattering experiments on KTN samples with different niobium concentrations. Simultaneously, the behaviour of the central peak, the soft mode (low frequency) and hard modes (high frequency) have been studied with light scattering as function of the temperature, the niobium concentration and the light polarization, specially in the vicinity of the structural phase transitions which were evidenced by other techniques. The results obtained by the various methods are in good agreement and interpreted, according to a phenomenological model, in terms of polarized clusters (ferroelectic microregions formed around the impurity), in relation with the phase transition mechanism. The physical origin of the additional Raman lines and the nature of the structural phase transitions are discussed. Raman measurements performed under applied electric field confirm this interpretation
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El Ghalia Bouziane. Etude par spectroscopie Raman de l'ordre polaire et des transitions de phase dans les solutions solides de KTa1-x NbxO3 (KTN). Autre [cond-mat.other]. Université Paul Verlaine - Metz, 1994. Français. ⟨NNT : 1994METZ021S⟩. ⟨tel-01776043⟩

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