Abstract

Fine particles of Al-doped lithium ferrite of general formula Li 0.5Al x Fe 2.5− x O 4 (0.0 ≤ x ≤ 0.4, in step of 0.1) were synthesized by the citrate gel auto combustion method and characterized using XRD, dielectric and impedance spectroscopy. X-ray diffraction studies confirmed that all the samples exhibit single-phase cubic spinel structure. The average particle size of as obtained samples has been found in the range of 38–41 nm. Dielectric permittivity, ac conductivity and complex impedance of all the samples were evaluated as a function of frequency and composition at room temperature. The variation of dielectric properties ɛ′, ɛ″, tan δ and ac conductivity ( σ ac), with frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general and the hopping of charge between Fe +2 and Fe +3. Interestingly, Al-doped nano-crystalline lithium ferrite samples exhibit a very large value for dielectric constant of the order of 10 5. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of Li 0.5Al x Fe 2.5− x O 4 ferrites. The analysis of data shows two semicircles corresponding to the grain and grain boundary volume suggesting that grain boundary is mainly involved in conduction mechanism. Magnetic properties have been measured by vibrating sample magnetometer (VSM) for all samples at room temperature.

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