The layered iron phosphate KMgFe(PO₄)₂: Crystal structure, Mössbauer spectroscopy and ionic conductivity

Abdessalem Badri (1) , Mourad Hidouri (1) , María Luisa López (2) , Maria Luisa Veiga (2) , Alain Wattiaux (3) , Mongi Ben Amara (1)

1 Matériaux Inorganiques
2 Departamento de Quimica Inorganica I, Facultad de Ciencias Quimicas
3 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux

A new iron phosphate, KMgFe(PO₄)₂ has been synthesized and investigated by X-ray diffraction, Mössbauer spectroscopy and ionic conductivity. This compound crystallizes in the monoclinic space group C2/c with the parameters a = 18.529(7) Å, b = 5.402(3) Å, c = 9.374(9) Å, β = 120.64(5)° and Z = 4. Its original structure can be described as the stacking along the [101] direction of [MgFe(PO₄)⁻₂]_∞ layers of corner-sharing MO₄ (M = 0.5 Fe + 0.5 Mg) and PO₄ tetrahedra. The K⁺ ions are occupying the inter-layer space. The Mössbauer spectroscopy confirms the occurrence of only tetrahedral Fe³⁺ ions and gives a definitive proof of the disordered character of their distribution. Ionic conductivity results obtained by the impedance spectroscopy technique show that this material is a two-dimensional ionic conductor, with low activation energy, 0.51 eV, that is interpreted on the basis of two-dimensional pathways.

Mots clés: Iron phosphate; Layered structure; X-ray diffraction; Mössbauer spectroscopy; Ionic conductivity

Domaines: Matériaux

Abdessalem Badri, Mourad Hidouri, María Luisa López, Maria Luisa Veiga, Alain Wattiaux, et al.. The layered iron phosphate KMgFe(PO₄)₂: Crystal structure, Mössbauer spectroscopy and ionic conductivity. Solid State Ionics, 2009, 180 (36-39), pp.1558-1563. ⟨10.1016/j.ssi.2009.10.012⟩. ⟨hal-00528914⟩