Investigation of structural, morphology, dielectric relaxation, and conduction mechanism of sodium diphosphate ε Na₄P₂O₇ compound

The physical properties of the sodium diphosphate ε Na₄P₂O₇ ceramic were investigated by X-ray diffraction (XRD), morphology, dielectric, and electrical measurements. Rietveld refinements of X-ray diffraction (XRD) data show that the compound crystallizes in the orthorhombic structure belonging to the space group Pmmm. Not only were the AC conductivity of our compound carried out at different temperatures and frequencies, but also its electrical modulus was evaluated, as well as the dielectric relaxation. On the other hand, the behavior of frequency exponent s of AC conductivity as a function of temperature is reasonably well interpreted by the correlated barrier hopping (CBH). In terms of CBH model, the values of maximum barrier height, hopping distance, and density of localized states are determined and discussed. A correlation between electrical and structural properties was also studied. Besides, the present results provide insights into the exploitation of sodium diphosphate ε Na4P₂O₇ as a promising cathode material for application in sodium-ion batteries.