Role of grain boundary in transport properties of LiCo3/5Mn2/5VO4 ceramics
Introduction
Spinel compounds with general formula AB2O4 (where A is metal ion with +1 or +2 valence and B is metal ion with (+3 or +4 or +5) valence) have many technological applications such as the use as electrode materials [1], magnetic materials [2], superhard materials [3], etc. Physical properties of the spinel compounds arise from the ability of these compounds to distribute the cations amongst the available tetrahedral A- and octahedral B-sites [4]. Among these, the spinel LiCoVO4 and LiNiVO4 has been investigated as one of the most promising cathode material for Li-ion secondary batteries because of its low cost, easy preparation and environmental advantages [1]. One such type of compound is LiCo3/5Mn2/5VO4 which is mechanically strong and environment friendly. Studying of electrical response in these materials is important too. Impedance measurements are normally used to characterize the electrical behavior of the materials. Using impedance analysis, it is possible to resolve the contributions and relative importance to electrical conduction and/or polarization of different phenomena that is taking place in the material in the frequency region. The electrical response of the material is evident as resistive and capacitive behaviors that signify the bulk grain, grain boundaries or defects present at electrode-material interface [5]. In the current paper, I present the study of electrical properties of LiCo3/5Mn2/5VO4 compound using complex impedance spectroscopy technique.
Section snippets
Experimental
Solution-based chemical method was used to prepare LiCo3/5Mn2/5VO4 fine powder. The detailed experimental procedure for material's formation and its pellets preparation has been described elsewhere [6]. The surface morphology of the gold-sputtered pellet (sintered at 575 °C for 2 h) was recorded with different magnifications at room temperature using a ZEISS (Model: SUPRATM 40) field emission scanning electron microscope. Subsequently, the pellets were polished by fine emery paper to make their
Structure/microstructure
The LiCo3/5Mn2/5VO4 ceramics shows an orthorhombic unit cell structure with lattice parameters of a=6.0401 (33) Å, b=8.8316 (33) Å, c=5.8653 (33) Å [6]. Fig. 1 displays a field emission scanning electron micrograph of the surface of sintered pellet sample. A polycrystalline texture of the compound is investigated from the nature of FE-SEM micrograph. It is also observed that grains of unequal sizes (∼0.2–2 μm) separated by well-defined grain boundaries are clearly visible and are distributed
Conclusions
The LiCo3/5Fe2/5VO4 was prepared by solution-based chemical method, whose electrical properties were investigated using ac technique of complex impedance spectroscopy (CIS). Surface morphology study shows polycrystalline nature of the material with grains of unequal sizes (∼0.2–2 μm) that are distributed homogeneously throughout the sample. Complex impedance study identifies: (i) grain interior, grain boundary and electrode-material interface contributions to electrical response (ii) the
Acknowledgment
The author is grateful to the Ferroelectrics Laboratory of the Department of Physics & Meteorology, Nanomaterials Laboratory of the Department of Chemistry and Central Research Facility, Indian Institute of Technology, Kharagpur-721302 (W.B.), India, for providing facilities to conduct experiments.
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2019, Journal of Molecular StructureCitation Excerpt :All the curves merge in high-frequency region (>0.5 106 Hz), and then Z′(Ω) becomes independent of frequency. This plateau region indicates a possible release of space charge as a result of the reduction in the resistive behavior of the material with the rise in temperature [39]. The variation of Z'' (Ω) of the impedance with angular frequency at various temperatures Fig. 7(b) reveals that Z″ values reach a maximum (Z″ max), which shifts to higher frequencies with the increase in temperature.