Doping Fe at the Co-tetrahedra site to improve the microstructure, optical, and Na-ion migrations in Na2Co1−xFexSiO4

Abstract

Na₂Co_1−xFe_xSiO₄ (NCFS)-based ceramics are some of the most promising alternatives to sodium-ion rechargeable batteries (SIBs). It was believed that the intrinsic qualities would be improved by the defect chemistry and the doping impact of iron in Na₂CoSiO₄ (NCS). In this study, Na₂Co_1−xFe_xSiO₄ with x = 0.1 and 0.2 sample structural characteristics, optical properties, ionic conductivities, and Na migration are examined. Contrary to the space group Pna2₁ undoped compound, the Rietveld refinement of the XRD patterns of NCFSs reveals an orthorhombic phase with the space group Pca2₁. It is discovered that the temperature dependence relaxation obeys the Arrhenius law, and the identical relaxation times for the charge transport mechanism are suggested by the weak separation of the activation energies for the two relaxation processes (R(A) and R(B)). The transportation behavior of Na⁺ in many chemical environments is made more favorable by Fe doping, and this has a significant impact on the electrical characteristics. As the Fe content increases, the conductivity increases as well. As the frequency increases, the frequency dependence of ac conductivity is examined to identify the conduction mechanisms such as OLPT, CBH, and inverse OLPT models.