Evaluation of NaFeTiO4 as an electrode for energy storage application
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We report a polycrystalline NaFeTiO4 prepared via conventional solid-state reaction route. X-ray diffraction (XRD) results and Rietveld refinement confirmed single-phase NaFeTiO4 having an orthorhombic unit cell with lattice parameters a = 9.17051 Å, b = 2.96310 Å, and c = 10.73676 Å and Pnma space group (No. 62). Energy dispersive spectrum (EDS) yielded sample stoichiometry that agrees well with its molecular formula. The surface morphology indicated a cylindrical rod-like microstructure comprising well-defined grains having variable dimension, i.e., diameter ~ 250 to 350 nm and length ~ 1 to 5 μm. Vibrational spectroscopy (FTIR/Raman) results indicated presence of FeO6 and TiO6 octahedra in good agreement with crystallographic study. Brunner-Emmet-Teller (BET) surface area measurement yielded a specific surface area as high as ~ 4.28 m2 g−1. Electrical impedance spectrum indicated presence of grains separated by well-defined grain boundaries in agreement with microstructural analysis. Electrical conductivity of the material was estimated to be ~ 6.05 × 10−6 S cm−1. The structural model obtained using XRD and vibrational spectrum results suggest layered tunnel/cage structure of cage dimension ~ 4.65 Å, along  direction in the xz plane, which is larger than the size of Na+ ion (0.98 Å). So, easier Na+ migration feasibility exists in NaFeTiO4 crystal lattice making it a good candidate for electrode applications.
KeywordsBatteries Sodium Electrodes Renewable energy Earth abundant
Biswajit Mandal is thankful to the Ministry of Human Resource and Development (MHRD, India) for the financial support. Authors are thankful to the instrument facility of the Indian Institute of Technology Patna for carrying out this work.
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