Evolution structurale en fonction de la température de monocristaux de solutions solides de KxRb1-xTiOPO4, 0<_x<_1 ; corrélation avec leurs susceptibilités électriques du second et du troisième ordre

Abstract : The structural study of KTIOPO 4 (KTP), RBTIOPO 4, K 0 . 8 8RB 0 . 1 2TIOPO 4 and K 0 . 4 6 5RB 0 . 5 3 5TIOPO 4 versus temperature (293-973 K) is obtained by single-crystal x-ray diffraction techniques at high resolution. Use and discussion of two different structural models permit to describe precisely the alkaline sites evolution and then to visualize the ionic path in conduction property of these compounds. Moreover, in solid solutions,the preferential occupancy of the rubidium ion on the two crystallographic independent sites (order-disorder phenomenon) is studied versus temperature. A simple model is developed and shows interactions which govern the evolution of that phenomenon. Finally, the variation in divergence of centrosymmetric structure of each compound, without considering alkaline sites, is similar : when temperature increases, the divergence is constant to reduce rapidly just before the phase transition. That variation is principally due to the bhaviour of TiO6 octahedra. The measurement of the second harmonic generation efficiency on KTP single-crystal versus temperature permits to obtain the variation of Deff2. That variation, similar to the divergence of centrosymmetry variation, shows that alkalines don't act, at least directly, in the high second-order dielectric coefficients of these compounds. Calculations, using Levine's model, confirm these results in showing the importance of TiO6 octahedral deformations. To characterize the interactions in KTP, an electron density study is performed and completed by a topologic analysis. Ti-O bonds characteristics in TiO6 octahedra are confirmed by LAPW calculations in simplified model.
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Theses
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http://docnum.univ-lorraine.fr/prive/SCD_T_1999_0177_DELARUE.pdf
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https://hal.univ-lorraine.fr/tel-01747090
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Submitted on : Thursday, March 29, 2018 - 10:50:49 AM
Last modification on : Monday, April 16, 2018 - 10:40:34 AM

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Patrice Delarue. Evolution structurale en fonction de la température de monocristaux de solutions solides de KxRb1-xTiOPO4, 0<_x<_1 ; corrélation avec leurs susceptibilités électriques du second et du troisième ordre. Autre. Université Henri Poincaré - Nancy 1, 1999. Français. ⟨NNT : 1999NAN10177⟩. ⟨tel-01747090⟩

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