Synthesis, crystal structure and optical investigation of the new phosphates: Na₇Mg₁₃Ln(PO₄)₁₂ (Ln=La, Eu)

Hasna Jerbi (1) , Mourad Hidouri (1) , Benoit Glorieux (2) , Jacques Darriet (2) , Alain Garcia (2) , Veronique Jubera (2) , Mongi Ben Amara (1)

1 Matériaux Inorganiques
2 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux

Two new isostructural rare earth phosphates Na₇Mg₁₃Ln(PO₄)₁₂ (Ln=La, Eu) have been synthesized and investigated by X-ray diffraction and optical measurements. They crystallize in the orthorhombic system with the Cmc2₁ space group (Z=4). The crystal structure exhibits a new type of framework built up from LnO₈ (Ln=La, Eu), MO₆ (M=0.5Mg+0.5Na) and MgO_x (x=5, 6) polyhedra and PO₄ tetrahedra linked by common corner, edge or face. It can be described in terms of [Mg₄MP₄O₂₂]_∞ layers stacked along the a direction. These layers are interconnected by [Mg₄LnP₄O₃₆]_∞ undulating chains spreading along the b direction. This framework delimits 6 distinct cavities occupied by Na⁺ cations. The results of the optical study of Na₇Mg₁₃La_1−xEu_x(PO₄)₁₂ (x=0, 0.02, 0.1, 1) reveal the presence of two different Eu³⁺ ion environments whereas the X-ray study predicts the existence of only one Eu site. This difference can be explained by the possible presence of the europium element in the sodium sites with small occupancies which cannot be detected by the X-ray structural determination.

Mots clés: Rare earth phosphates; Chemical synthesis; X-ray diffraction; Optical properties

Domaines: Matériaux

Hasna Jerbi, Mourad Hidouri, Benoit Glorieux, Jacques Darriet, Alain Garcia, et al.. Synthesis, crystal structure and optical investigation of the new phosphates: Na₇Mg₁₃Ln(PO₄)₁₂ (Ln=La, Eu). Journal of Solid State Chemistry, 2010, 183 (8), pp.1752-1760. ⟨10.1016/j.jssc.2010.05.010⟩. ⟨hal-00515588⟩