Synthesis, crystal structure and magnetic properties of Fe2Pb3−xBax(PO4)4 (0≤x<3)

Abstract

Abstract The new solid solution Fe 2 Pb 3− x Ba x (PO 4 ) 4 has been synthesized by the solid reactions. In the whole experimental range (0≤ x T =850 °C), this solid solution is isotypic to the pure phase Fe 2 Pb 3 (PO 4 ) 4 . This compound crystallizes in the monoclinic space group P 2 1 / c , with a =9.0106(6) A, b =9.0632(7) A, c =9.3101(7) A, β =116.867(3)° and Z =2. The structure has been determined from a single crystal and refined to R =0.075. The Fe 2 Pb 3 (PO 4 ) 4 structure can be described as a three-dimensional array containing isolated [Fe 3+ O 6 ] octahedra connected through PO 4 tetrahedra, enclosing a network of cavities where the lead cations reside. Fe 2 Pb 3 (PO 4 ) 4 is antiferromagnetic below T N =30 K; this is consistent with the fact that the main magnetic interactions are Fe–O–P–O–Fe superexchange. The room temperature Mossbauer spectrum exhibits a common place Fe 3+ signal ( δ =0.45 mm/s, Δ =0.32 mm/s). The substitution of the Pb 2+ by Ba 2+ cations increases the cell volume in good agreement with the variation of their ionic radius.