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Analyse expérimentale et théorique du spectre Raman dans la phase cubique de la solution solide KTa1-xNbxO3

Abstract : The dynamical properties of solid solution KTa1-xNBxO3, presenting a structural phase transition for niobium concentration higher than 0.8 %, have been studied systematically as a function of temperature and niobium concentration. This study has been carried out experimentally by Raman spectroscopy in the cubic phase and as function of symmetry. The intense Raman spectrum shows the same strucutres than in pur KTaO3. It can be attributed essentially to second order diffusion, and the introduction of niobium ion do not modify it basically. These experimental results have been analysed in the framework of an anharmonic dynamical shell model. The non-linearity is treated in terms of fourth-order electron-phonon coupling, localized on the oxygen ions, which means in fact, a non linear polarisability of these ions. Our calculations show that these couplings which explain accurately the softenning of ferroelectric mode, are also responsible for the strong second order Raman spectrum observed in the cubic phase. Indeed, the various structures, their profile, their behaviour with temperature, symmetry and concentration of niobium ions are well reproduced within the framework of this model
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Submitted on : Tuesday, April 24, 2018 - 3:40:45 PM
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  • HAL Id : tel-01775707, version 1



Hocine Mesli. Analyse expérimentale et théorique du spectre Raman dans la phase cubique de la solution solide KTa1-xNbxO3. Matière Condensée [cond-mat]. Université Paul Verlaine - Metz, 1986. Français. ⟨NNT : 1986METZ016S⟩. ⟨tel-01775707⟩



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