Contribution à l'étude des propriétés optiques et structurales de solutions solides de niobates de potassium et de lithium K6Li4Nb10O30 (KLN) et de niobates et tantalates d'argent AgNb(x)Ta(1-x)O3 (ATN) pour apllications diélectriques hautes fréquences et génération de seconde harmonique

Abstract : The physical properties of the tungsten bronze compound K6Li4Nb10O30 (KLN) and the perovskite compound AgNb(x)Ta(1-x)O3 (ATN), based on the common NbO6 octahedra, were studied theoretically and experimentally. These two families are intensively studied for their strong optical non linearities, suitable for laser beams generation and processing. In section A, a non destructive characterisation process of Nb excess in our samples was performed. It was based on a Raman spectroscopy study and a second harmonic generation study on KLN crystals, A correlation between the frequency of a characteristic mode and Nb excess was evidenced. The Raman spectroscopy study pointed out the possible presence of an overdamped soft mode near the ferroelectric-paraelectric phase transition. Moreover, the Nb concentration of our samples was confirmed by a non collinear phase matching study in SHG experiments. Owing to the extraordinary refraction index strong dependence on Nb concentration, a non critical phase matching can be performed by choosing the Nb content. The KLN system seems to be a promising material for frequency doubling integrated wave guides. In section B of the thesis, the dynamical properties of the perovskite compound AgNb(x)Ta(1-x)O3 (ATN) were analysed. Thanks to a collaboration with Russian (Moscow), Lithuanian (Vilnius) and polish (Katowice) laboratories, a study of the dielectric response of this system, on a broad frequency range ((1 MHz - 30 THz), evidenced the following facts : a high frequency (0.5 THz) dielectric dispersion occurs, the dispersion exhibits a relaxational nature involving the Nb5+ ions. This dispersion was described by two kinds of response functions., the control of Nb/Ta substitution can be used to set dielectric permittivity from 100 to 700 without losses in the 1 MHz - 100 GHz range, making ATN compound very interesting for high frequency dielectric devices. At last, in section C, a general discussion on the physical origins of the phase transitions and optical non linearities in the tungsten bronze and the perovskite compounds is presented. The role of NbO6 octahedra on these properties has been evidenced on the basis of the results of sections A and B, and on literature data
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Wulfran Fortin. Contribution à l'étude des propriétés optiques et structurales de solutions solides de niobates de potassium et de lithium K6Li4Nb10O30 (KLN) et de niobates et tantalates d'argent AgNb(x)Ta(1-x)O3 (ATN) pour apllications diélectriques hautes fréquences et génération de seconde harmonique. Autre [cond-mat.other]. Université Paul Verlaine - Metz, 1996. Français. ⟨NNT : 1996METZ037S⟩. ⟨tel-01777146⟩

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