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

The new solid solution Fe2Pb3-xBax(PO4)(4) has been synthesized by the solid reactions. In the whole experimental range (0 <= x < 3, T=850 degrees C), this solid solution is isotypic to the pure phase Fe2Pb3(PO4)(4). This compound crystallizes in the monoclinic space group P2(1)/c, with a=9.0106(6) angstrom, b=9.0632(7) angstrom, c=9.3101(7) angstrom, beta=116.867(3)degrees and Z=2. The structure has been determined from a single crystal and refined to R=0.075. The Fe2Pb3(PO4)(4) structure can be described as a three-dimensional array containing isolated [Fe3+O6] octahedra connected through PO4 tetrahedra, enclosing a network of cavities where the lead cations reside. Fe2Pb3(PO4)(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 Fe3+ signal (delta=0.45 min/s, Delta=0.32 mm/s). The substitution of the Pb2+ by Ba2+ cations increases the cell volume in good agreement with the variation of their ionic radius. (c) 2005 Elsevier B.V. All rights reserved.