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Synthèse et caractérisation physico-chimique de nouveaux phosphates de magnésium : (A¹₂ ou B²)Mg₂M³(PO₄)₃ (A = Na, Ag ; B = Ca, Pb, Sr, Ba ; M = Fe, In)

Abstract : This study is a part of contribution to the investigation program aiming to elaborate and to characterize new phosphate-based materials, particularly, with the alluaudite and/or α- CrPO₄ type structure. These compounds are characterized by their wide physico-chemical properties that they can exhibit in several fields of application such as catalysis and electrochemistry.We have isolated and determined the structure of eleven new phosphates by means of single crystal X-ray diffraction.The phosphate PbMg₃(HPO₄)(PO₄)₂ was synthesized by hydrothermal method. Its structure was resolved in monoclinic system with space group I2/m.The substitution of one cation Mg²⁺ by Fe³⁺ has allowed us to isolate five new compounds using solid-state diffusion method. Four compounds of general formula MMg₂Fe(PO₄)₃ (M = Ba, Sr, Pb, Ca) exhibit two different structural types. The Sr or Ba based compounds are related to the α-CrPO₄ type structure and crystallize with the space group Imma of the orthorhombic system. Besides, the Ca or Pb based phosphates crystallize with the P21/n space group of the monoclinic system. The fifth phase, namely Ca₂MgFe₂(PO₄)₄, crystallizes in orthorhombic system with a Pbca space group.Finally, we have succeeded to synthesize five new Mg, Fe and monovalent elements based phosphates, namely NaMg₃(HPO₄)₂(PO₄), Na₂Mg₂Fe(PO₄)₃, Ag₁,₆₇Mg₂,₃₃Fe₀,₈₉(PO₄)₃, Na₁,₈₅Mg₁,₈₅In₁,₁₅(PO₄)₃ and Ag₁,₆₉Mg₁,₆₉In₁,₃₁(PO₄)₃, using both the hydrothermal and the solid-state diffusion methods. All these phosphates crystallize in the monoclinic system with C2/c space group and are similar to the alluaudite type structural. The powder of stoichiometric compounds A₂Mg₂Fe(PO₄)₃ (A = Na, Ag) were synthesized by solid-state method and characterized by X-Ray powder diffraction. Conductivity’s studies by impedance spectroscopic method have allowed determining values for Na₂Mg₂Fe(PO₄)₃ (σ = 0.12.10⁻⁴ S.cm⁻¹ at 500°C) and for Ag₂Mg₂Fe(PO₄)₃ (σ = 4.10⁻³ S.cm⁻¹ at 500°C) due to cations migration in the channels of the structure.
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Submitted on : Tuesday, October 5, 2021 - 4:20:33 PM
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Ahmed Ould Saleck. Synthèse et caractérisation physico-chimique de nouveaux phosphates de magnésium : (A¹₂ ou B²)Mg₂M³(PO₄)₃ (A = Na, Ag ; B = Ca, Pb, Sr, Ba ; M = Fe, In). Matière Condensée [cond-mat]. Université de Valenciennes et du Hainaut-Cambrésis; Université Mohammed V (Rabat), 2018. Français. ⟨NNT : 2018VALE0045⟩. ⟨tel-03366381⟩

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