Structure of AFeTi(PO4)3 (A = Mn, Sr) Nasicon-type phases

AFeTi(PO4)(3) (A= Mn, Sr) materials were obtained by solid state reaction in air at 1000 degrees C. The structures of the two compounds were determined from X-ray powder diffraction data (XRD) using Rietveld analysis. Both phases exhibit the Nasicon-type structure (R 3 c space group) with a statistical Fe(Ti) distribution within the framework. Their hexagonal cell parameters are : a(hex). = 8.529(1) angstrom, C-hex. = 20.950(2) angstrom and a(hex). = 8.443(1) angstrom, C-hex = 22.543(2) angstrom, for MnFeTi(PO4)(3) and SrFeTi(PO4)(3), respectively. Sr atoms occupy only the M1 site in SrFeTi(PO4)(3). From XRD data, it is difficult to distinguish without ambiguity between Mn2+, Fe3+ and Ti4+ ions in MnFeTi(PO4)(3). Nevertheless from the cation-anion distance values found from the structure determination, the Mn2+ distribution within the M I site of Nasicon structure is validated.