Ionic behavior, Na+ mobility and infrared spectroscopy in Na7Cr4(P2O7)4PO4 material

The title compound, heptasodium tetrachromium(III) tetrakis(diphosphate) orthophosphate, was synthesized by solid state reaction. Its structure is isotypic with that of Na7M4(P2O7)4PO4 (M = In, Al) compounds and is made up from a three-dimensional [(CrP2O7)4PO4]7- framework with channels running along [001]. The Na+ cations are located in the voids of the framework. This compound has been investigated by X-ray diffraction and infrared (IR) spectroscopy. The conductivity measurements of the compound were carried out from 515 to 795 Kelvin using the frequency response analyzer with 0.05V amplitude signal over the range of 13MHz-5Hz. The conductivity of the sample at 574K is 0.45 10-6 S.cm-1. The activation energy Ea=0.73eV shows that Na7Cr4(P2O7)4PO4 is a medium ionic conductors. The monovalent cations conduction pathways in the crystal bulks are simulated by means of the bond valence model (BVS)