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Cristallogénèse et étude structurale, thermodynamique et spectroscopique des malates hydrogénés de lithium et d'ammonium : rôles des groupements organiques et des liaisons hydrogène dans les propriétés vibrationnelles

Abstract : The studies on salts of malic acide scarce if one excepts structural determinations. This is especially the case for vibrational properties. Before the present work, this kind of investigations did not exist for lithium dimalate. The two salts of malic acid, which are the object of the present thesis, lithium dimalate (C4H6O5,C4H5O5-, Li+)DML) and ammonium malate (C4H5O5-,NH4+) (MA), exhibit layered structures. Links between the layers are provided by a number of hydrogen bonds. We have synthesised these crystals and made the necessary controls of their structure. We have focused our attention particularly on hydrogen bonds. The differential scanning calorimetry showed that the breaking of the hydrogen bonds is responsible of the relatively low melting point of those compounds. The same study allowed the determination of the global energy of this kind of bonds for the two crystals. We have calculated the frequencies of the O...O stretching modes of the hydrogen bonds and the results are in agreement with the modes observed by raman spectroscopy. The high frequencies of the O-H stretching modes have also been studied experimentally. The high temperature raman spectra, as well as the low temperature ones, showed the stability of the monoclinic structure of DML and of the orthorhombic structure of MA from 10K to the beginning of the melting process around 423K. No phase transition has been detected. An assignment has been proposed for most of the internal modes observed by raman spectroscopy. The infrared reflectivity studies showed the weakness of the coulomb forces for both DML and MA ; the observed LO-TO splittings are small. As a first attempt, we have undertaken a lattice dynamical calculation with a simple De Launay type central force model. However, this model needs improvements, for example angular deformations could be taken into account
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Madjid Kemiche. Cristallogénèse et étude structurale, thermodynamique et spectroscopique des malates hydrogénés de lithium et d'ammonium : rôles des groupements organiques et des liaisons hydrogène dans les propriétés vibrationnelles. Autre [cond-mat.other]. Université Paul Verlaine - Metz, 1994. Français. ⟨NNT : 1994METZ065S⟩. ⟨tel-01776855⟩

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