Electrical and dielectric properties of Si₅P₆O₂₅: Experimental study and simulation of oxygen pathways migration

Silicophosphate, prepared from Tunisian siliceous sand, has been investigated as a potential oxide ion conductor. XRD and Rietveld refinement analyses confirm the formation of pure single-phase Si₅P₆O₂₅ that crystallizes in the trigonal system with R-3 space group. The electrical conductivities and dielectric properties of this material have been studied using complex impedance spectroscopy from 10 to 10⁶ Hz at a temperature range from 600 to 680 °C. The results show that the ionic conductivity σ_dc increases from 5.43 × 10^− 5 S.cm^− 1 at 600 °C to 0.23 × 10^− 3 S.cm^− 1 at 680 °C with an activation energy of 1.33 eV. The frequency dependence of AC conductivity could be explained by Jonscher’s power law. The dielectric constant’s decrease with frequency indicates a region of dispersion resulting from a polarization process’ relaxation. The simulation of the oxygen conduction using the Bond Valence Site Energy (BVSE) model shows the presence of four interstitial sites used with equilibrium sites to form a zigzag isosurface of oxygen migration. The calculated activation energy is about 1.43 eV.