Le nitrate double NaRb2(NO3)3, composé intermédiaire du système binaire isobare NaNO3 + RbNO3: études thermiques et cristallographiques
Crystallographic and thermodynamic investigations of the binary (NaNO3 + RbNO3) phase diagram at atmospheric pressure reveal the existence of an intermediate compound NaRb2(NO3)3 (sodium dirubidium trinitrate) previously predicted and now reported experimentally for the first time. According to a DSC analysis, the compound exhibits three allotropic forms. In its low-temperature allotropic form (α form, orthorhombic) there are two Rb (m.. site symmetry) and one Na (m..) independent crystallographic positions and three planar nitrate groups. The bond-valence-sum calculations for all atoms agree well with their oxidation states. The Rb cations are located in the (100) plane at x = ½ with 11 oxygen coordination. The Na ones are in the same plane at x = 0 and are coordinated to eight O atoms from six nitrate groups. The charge-distribution method has been used to evaluate the degree of distortion of the alkali polyhedra.
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Document Type: Research Article
Université de Tunis El Manar, Faculté des Sciences, Laboratoire de Thermodynamique appliquée, El Manar II, 2092 Tunis, Tunisie
Université de Tunis El Manar, Faculté des Sciences, Laboratoire de Matériaux et Cristallochimie, El Manar II, 2092 Tunis, Tunisie
January 1, 2015