Layered ordering of vacancies of lead iron phosphate Pb3Fe2(PO4)4

Lead iron phosphate Pb3Fe2(PO4)4 has been synthesized by solid state method and characterized by X-ray powder and electron diffraction, differential scanning calorimetry, Mössbauer and infrared spectroscopy. A structural model for Pb3Fe2(PO4)4 is proposed and is refined by the Rietveld method. The compound crystallizes in the monoclinic space group P21/c with a=9.0065(6)Å, b=9.0574(6)Å, c=9.3057(6)Å, β=116.880(4)°, V=677.10(8)Å3, Z=2, Rwp=3.52%, Rp=2.66%. It exhibits a structure with a three-dimensional open framework. The 3D framework is formed by PO4 tetrahedra and FeO6 octahedra connected via common vertices. ¾ of cavities in the framework are occupied by lead and ¼ are vacant.