Structural study and properties of a new iron phosphate Rb9Fe7(PO4)10

Abstract: Synthesis, single crystal X-ray diffraction, Mössbauer and magnetic studies of a new iron phosphate Rb9Fe7(PO4)10 are described. This compound crystallizes in the monoclinic system with the space group P21/a and the following parameters: a =9.886(4)Å, b =16.493(2)Å, c =13.437(2)Å, β =110.49(3)° and Z =2. Its structure is closely related to that of the Cs9−x K x Fe7(PO4)10 phosphates. The 3D framework consists of FeO6 and FeO5 polyhedra and Fe2O10 units of corner-sharing FeO6 and FeO5 polyhedra. These units are linked to each other by the phosphate tetrahedra in such a way that the resulting framework forms large intersecting tunnels extending along the a and c directions, where the Rb+ cations are located. A high temperature X-ray powder diffraction study showed a partial decomposition of the product above 773K. The magnetic susceptibility results are consistent with Fe(III) showing an antiferromagnetic ordering below T N ≈19K and a paramagnetic behavior in the range of 50–300K. The application of the Curie–Weiss law yields an effective moment of 5.99μB in a good agreement with the ideal spin only value of 5.92μB for d5-iron(III). The distribution of iron and its local environments were confirmed by a Mössbauer study undertaken at 293 and 4.2K. [Copyright &y& Elsevier]