Spectroscopic characterization of mixed cation diphosphates of the type MIFeIIIP2O7 (with MI=Li, Na, K, Rb, Cs, Ag)

The mixed cation diphosphates of composition MIFeIIIP2O7 have been prepared using the so called co-precipitation method starting with Fe(III) and M(I) nitrate solutions and solid (NH4)H2PO4, and characterized by X-ray powder diffractometry. The infrared and Raman spectra of the compounds were recorded and the results are briefly discussed on the basis of their structural peculiarities. The 57Fe-Mössbauer spectra show that the typical high-spin FeIIIO6 octahedra existent in these compounds exhibit almost no distortion. However, the hyperfine parameters are sensitive to some characteristics of the MI cations and to the different structural types.

► Diphosphates of composition MIFeIIIP2O7 were prepared by the co-precipitation method.
► IR and Raman spectra could be interpreted on the basis of the known structures.
► Small structural differences between these compounds were spectroscopically detected.
► 57Fe-Mössbauer spectra show that the FeIIIO6 octahedra are only weakly distorted.