Preparation and characterization of LiFe_(1/2)Ni_(1/2)VO_4

摘要

A layered ceramic oxide, LiFe_(1/2)Ni_(1/2)VO_4 has been prepared using solid-state reaction technique. The preparation conditions have been optimized using thermogravimmetric analysis (TGA) studies. The formation of the material sample under the reported condition has been confirmed by X-ray diffraction (XRD) analysis. XRD analysis indicates the crystal structure to be orthorhombic with lattice parameter: a = 3.5637 A, b= 17.7486 A, c = 12.2884 A. The phase morphology and surface properties studied using scanning electron microscopy (SEM), suggest a polycrystalline texture with reasonable number of the voids. Complex impedance analysis of the sample has indicated: (ⅰ) conduction due to bulk contribution at T ≤ 200℃, (ⅱ) the presence of grain boundary effects at T ≥ 200℃, (ⅲ) negative temperature coefficient of resistance (NTCR) behaviour and (ⅳ) evidence of temperature dependent electrical relaxation phenomena in the sample. The DC conductivity (σ_(DC)) shows typical Arrhenius behaviour when observed as a function of the temperature. The activation energy value has been estimated to be 0.42 eV. σ_(DC), as evaluated from complex impedance spectrum, shows a jump of nearly ～4 orders of magnitude in the value at higher temperature when compared to that of the room temperature value. AC conductivity spectrum obeys Jonscher's universal power law. The results of σ_(AC) as a function of frequency are also discussed.