Effect of Iron Doping on the Conductivity of Biphasic Sodium Titanate –potential Sodium Ion Conductor

Abstract

The effect of iron doping on the conductivity of sodium titanate, a material suitable for its purported use in sodium-ion batteries, was explored. The sodium titanate and sodium iron titanate materials were prepared by a simple sol–gel aqueous coprecipitation route, followed by calcination at 1273 K. The material was characterized using thermogravimetric-differential thermal analysis (TG-DTA) for understanding the thermal decomposition behavior, X-ray diffraction (XRD) for the crystalline phase composition analysis, scanning electron microscopy (SEM) for understanding the surface morphology and homogeneity of the phases and X-ray photoelectron spectroscopy (XPS) for establishing the oxidation states of different ions. The electrochemical impedance spectroscopy (EIS) studies revealed an increase in total conductivity at low levels of iron doping. The activation energy of conduction was derived to be approximately 0.2–0.3 eV, which was significantly lower than the reported values for undoped sodium titanates, 0.7 eV for Na₂Ti₃O₇ and 0.9 eV for Na₂Ti₆O₁₃, indicating enhanced ionic conductivity upon iron incorporation. Overall, the findings of this study provide a fundamental understanding of the variation in conductivity of sodium iron titanate with iron concentration and its correlations with different crystalline phases.