Raman and FTIR studies of the structural aspects of Nasicon-type crystals;: AFeTi(PO4)3 [A = Ca, Cd]

Raman and FTIR spectra of CaFeTi(PO4)(3) and CdFeTi(PO4)(3) are recorded and analyzed. The observed bands are assigned in terms of vibrations of TiO6 octahedra and PO4 tetrahedra. The symmetry of TiO6 octrahedra and PO4 tetrahedra is lowered from their free ion symmetry. The presence of Fe3+ ion disrupts the Ti-O-P-O-Ti chain and leads to the distortion of TiO6 octrahedra and PO4 tetrahedra. sThe PO43- tetrahedra in both crystals are linearly distorted. The covalency bonding factor of PO43- polyanion of both the crystals are calculated from the Raman spectra and compared to that or other Nasicon-type systems. The numerical values of covalency bonding of factor indicates that there is a reduction in redox energy and cell voltage and is attributed to strong covalency PO43- polyanionin. (C) 2008 Elsevier Ltd. All rights reserved.