Synthesis and characterization of a new iron phosphate KSrFe2(PO4)3 with a langbeinite type structure

Synthesis, crystal structure, Mössbauer spectroscopy and magnetic susceptibility of a new phosphate KSrFe₂(PO₄)₃ are described. This compound crystallizes with the unit cell parameter a = 9.809(2) Å of the cubic space group P2₁3 and four formula units per cell. Its structure belongs to the well known langbeinite type. It consists of a 3D framework resulting from a corner-sharing between FeO₆ octahedra and PO₄ tetrahedra. This framework delimits two distinct cavities, statistically occupied by the K⁺ and Sr²⁺ ions. The Mössbauer spectroscopy gave clear evidence of the exclusive presence of octahedral Fe³⁺ ions. The magnetic susceptibility measurements revealed that the compound follows the Curie-Weiss behavior with an experimental effective moment per unit formula μ = 8.16 μ_B, consistent with the ideal spin only value of 8.37 μ_B.